Use of epoxy for levelling

[Neale]

Thanks to various contributors, I have been able to get a lot of useful information about using epoxy for rail levelling. However, it is usually buried deep within build logs, so I wanted to start a thread just for this topic, if only to make it easier to find later!

After reading lots of views on the subject, I ended up with Reactive Resins Syntac EPAFD low-viscosity resin and matching Synamin 201-c slow hardener. I calculated the required volume based on width/length of area to be filled and a guess at a sensible depth (5mm), and based on 1ml weighing 1g (which I now realise is a big assumption and not based on any known density...) I mixed up 500g of resin and 250g hardener, which should have filled the required area with a bit left over. To my surprise, this is exactly what happened.

This is an overall view of my machine (very much work-in-progress).

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Top rails are about 1800mm, spaced at about 1000mm. Construction is all-welded, a mix of 50x50x3 and 100x50x3. As far as I can judge, the X rails dip in the middle by about 1.3mm. I don't know if this is welding distortion, or if the original box section was slightly bent.

I used a single central bridge, an odd length of MDF that was about the right size. It is screwed to some odd bits of batten, clamped to the rails so it is level with the rail surface.

14031

The dam uses Screwfix thick draught excluder, which stuck well. To avoid leaks in the corners, I used small dabs of hot-melt glue. I tested this first, in case it melted the draught excluder, but it seemed OK and worked well. The only leak, in fact, was over a couple of the plug welds that hold a 25x5 strip in the top of the rails (to take the tapped holes later). There was clearly a very slight weep through these. This shows the hot-melt glue, and the sink hole close to one end over a plug weld.

14030

I don't expect this to be a big problem later.

There were a couple of things that were worrying me before I started. One was the horror stories of shrinkage, especially at rail/bridge joins. I didn't see any evidence of this.

14032

One thing that I did do was to run up and down the epoxy with a small stick once I had poured it, to encourage it to find its own level. I think that that might explain the visible stripes in the epoxy at the join, although you can't feel them on the surface. I could also remove almost all the bubbles by poking them with the stick.

The other main worry was whether the epoxy would set or not, given the drop in UK temperatures over the last week or so. I decided to go ahead anyway, and for a small part of the time built a tent over the machine and blew in hot air from a small fan heater. However, I wasn't happy running this when I wasn't in the garage, so it didn't get a lot of this. In practice, this only took it up to 15C or so. However, as far as I could tell, the temperature in the garage varied between about 8C and 12C; the minimum temperature for the resin is given as 8C so it wasn't too bad. After 24hr, I could leave a fingerprint on the resin which largely disappeared over a few hours. After 72hr, it would mark with a fingernail. After 6d, I peeled back some of the dam on the bridge and tried scraping the meniscus as an experiment and it seemed pretty hard.

14033

I'm now feeling fairly comfortable about being able to start drilling/tapping and mounting the rails.

[EddyCurrent]

Rather than copy it all out I thought it would be acceptable to put a link to my epoxy experience. This is where it starts;
http://www.mycncuk.com/threads/6565-Ready-Steady-Eddy?p=54024#post54024

[Neale]

Rather than copy it all out I thought it would be acceptable to put a link to my epoxy experience.


Thanks, Eddy - even the search facility on the forum just takes you to the start of a 34-page thread! It's the problem with build logs - the most useful ones are the ones where it's most difficult to find what you know is there...

[Beone]

NASA calls it "conformal shimming"
dave

[Neale]

I had no idea just how level epoxy levelling left the surface so I checked one of my rails this evening. About 1750mm long, joined to the opposite rail about 1000mm away via a single central bridge. Epoxy around 4-5mm deep (there was a dip in the middle of the 100x50 box section rail support of about 1.5mm). Once set, I removed the meniscus from the epoxy with a coarse file and also ran the file over the top of a few bubbles that had formed.

For checking, I used a precision level plus feeler gauges, resting on a couple of ball carriages on the profile rail bolted directly on top of the epoxy. Using a 200mm level, I measured the deviation from level at 200mm intervals along the rail, then calculated the variation from a straight line between the two ends of the rail (which were about 4 thou different in height. This was because I had moved the frame slightly from when the epoxy was first poured.) I'm sure that there was plenty of scope for errors to creep in, but at least it gives a feel for the overall magnitude of the errors. I'm sorry for the mixture of imperial and metric units in this post but I still can't get a grasp of the magnitude of small measurements once you are down to tens of microns and I have to go back to "thou".

I was surprised by how good the results were. Remembering that these figures are variations from a straight line between the two rail ends, the maximum variation from "flat" was about 7 thou corresponding to a dip in the middle of the rail and smoothly rising towards each end. Given that this resulted from an epoxy self-levelling along a long, narrow 1750x30x5 "channel", and even though fairly runny by epoxy standards it's still not quite like water, that seems pretty good. Knowing the numbers gives me more confidence in moving forwards, and I'm planning now to use epoxy levelling on the gantry as well.

[gavztheouch]

Would it be possible to use a shallower bed of epoxy? 5mm seem like a lot?

[JAZZCNC]

Would it be possible to use a shallower bed of epoxy? 5mm seem like a lot?

Yes just mix Less epoxy.!!.:hysterical:

[njhussey]

As long as there's enough to level then that's all that really matters as long as there's enough steel to tap into. The epoxy adds to the depth of the tapping...

[gavztheouch]

Cool sounds good, this is going to be for a laser cutter. I need quite a large surface area to mount the rails, laser tube and optics so the thinner the better. I think I might drill through holes rather than tap the holes so I have a bit of jiggle room, nylock bolts would be nice to use too.

[Neale]

I wasn't sure how deep to make the epoxy but 5mm, maybe a touch less, at the deepest seemed to be about right while leaving an adequate depth at the shallowest points. I wonder if the roughly 7 thou variation is due to the change in depth along the length of the rail - there is a slight dip in the epoxy surface where the epoxy is deepest. Might be coincidence - don't know. I was concerned that the epoxy should be deep enough that the self-levelling would work; I had a feeling that the epoxy might not flow quite as freely if it were too shallow. Again, this is conjecture and not tested. I was not concerned about depth as far as tapping was concerned; the epoxy drills easily (rather more easily than the steel, anyway) and I would not expect unfilled epoxy to hold a decent thread. Although I used 3mm box section, there is a 25x5mm strip inside the box section to give depth for threading. I drilled the box section and plug-welded the strip in place using an improvised wedge arrangement to hold the strip against the inside of the box for welding. In retrospect, I should have used Eddycurrent's "glue it in place" technique. Once tapped and bolted, it ain't going anywhere...

Another variable to play with is epoxy strip width. I used draught excluder tape to make the dam and with the aid of hot-melt glue to plug any joins, it worked well. However, it leads to a narrower strip. Njhussey's technique with MDF walls glued to the sides of the box section clearly gives a wider strip. Personally, I believe that the narrower strip (as long as it is wide enough to support the rail) works fine and is perfectly adequate but it does make it essential to remove the meniscus which has to be done without damaging the surface that will take the rail. A wider strip means that the meniscus will not interfere with the rail mounting, and in any case there is more room to hack at the meniscus without damaging the surface. My way uses less epoxy, and I didn't have any problems taking a coarse file to the edges but that doesn't mean that it's the best way.

I'm sure that the epoxy technique would work well for a differently-shaped area. My experience suggests that the epoxy does not level itself absolutely but it might be better over a square area rather than a long thin area. Additionally, I wonder if large variations in depth affect the top surface so doing the filling in two passes - the first gives a "nearly there" surface and the second corrects any minor residual error - might help. Or be ready to shim out the odd thou or two at the end if you need a really flat surface, but the epoxy will still get you closer than any technique other than machining or grinding. Even a slab of Ecocast will need to be mounted carefully to avoid deflection when bolted down.


NASA calls it "conformal shimming"
...and I shall be doing that with epoxy putty when it comes to mounting the gantry feet to the plates bolted to the tops of the X carriages!

[Jonathan]

Neale, your readings of the resin accuracy are interesting. Seves thou is 7*0.0254=0.18mm which is a bit more than I'd expect (though by no means a showstopper). Did you see the readings for the expoxy 'straightness' I took in my build log?

http://www.mycncuk.com/attachment.php?attachmentid=14208&stc=1
Towards the end of that graph there is a large negative deviation. It turns out this was not actually the case - the bearing block was rubbing on the aluminium epoxy barrier which pushed it out of line for the last 100mm or so. Either way, the deviation is very small...

[Neale]

Here is the corresponding error plot for my rail (as I have only managed to fix down one rail so far. Once visitors have left...)

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I have converted to mm for ease of comparison. We used different resins, although I'm inclined to dismiss that one as a significant factor - they are both at the runny end of the epoxy viscosity scale. However, I was working at an ambient temperature of around 10C at the time of pouring and although I had kept the resin indoors for a few days beforehand, it was a thin film sitting on steel and will have been down to garage ambient almost immediately. That won't have done wonders for viscosity and maybe it didn't flow as well. I think my rail section error was also rather greater to start with, and as my errors are roughly aligned with the initial error (the bends in the rail) I wonder if these are linked. Better flow where the epoxy is deeper?
There is also the measurement technique to consider. I don't have a surface plate big enough to be useful - mine's a sheet of thick plate glass about 300mm square - so I used a level at a series of points, combining level scale readings with feeler gauges to get a "difference in height" value. I dropped all these into a spreadsheet to get the graph shown here. It wouldn't be difficult to calculate shim values to bring the rail into line. Is it worth it? Assuming, obviously, that the bed is finished to the rails, then a hump in the middle wouldn't be a problem as the workpiece would tend to droop over it, being clamped at the edges. However, it is more likely to bridge a hollow in the bed. And I'm quite certain that my sophisticated woodworking techniques would dramatically fail with an error of 0.18mm in depth over a 1.8m length...

[EddyCurrent]

Here is the corresponding error plot for my rail (as I have only managed to fix down one rail so far. Once visitors have left...)

Slip of the keyboard I expect, but Jonathan's was 'Height Deviation' i.e. vertical, while your graph says 'Error from Horizontal'.

[Neale]

Slip of the keyboard I expect, but Jonathan's was 'Height Deviation' i.e. vertical, while your graph says 'Error from Horizontal'.

What was going through my mind was "height error from horizontal plane". What I should have said is beyond me at this hour, but I knew what I meant:beer:

[Neale]

This post is probably going to open me up to derision from the practical community ("that's close enough, why are you bothering about 7 thou?") and the more academic ("your sums are wrong and your measurements are suspect!") but I'm feeling brave so here's my theory.

I believe that the dip in the surface of my epoxy is due to shrinkage, and there is a lesson to be drawn from that in how you should use epoxy. This evening, I measured, as closely as my measuring kit would allow, the depth of the epoxy bed at the end and the centre of my X rail. If I assume that the difference in level is due to shrinkage, the difference in levels of the hardened epoxy corresponds to a shrinkage amount of approximately 10%. That is, after setting, the epoxy bed will end up about 90% of the depth of the liquid resin. That's using the resin as per the first post of this thread. I suspect that a nominal 10% linear shrinkage will not lead to an exact 10% reduction in depth as there will be other smaller effects due to shrinkage across as well as down through the epoxy but I'm ignoring three-dimensional effects for the moment. I'm happy to go through how I did my calculations if asked, but for the moment I'll skip directly to my conclusions.

An application of this epoxy will lead to a reduction in "depth" errors by an amount dependent on the shrinkage factor of the epoxy used. In my case, for example, I started with a dip in the rail surface of about 1.7mm; after epoxy treatment I ended up with a dip of about 0.18mm, a reduction of about 90%. If you think about it, this will happen whatever the depth of epoxy used (unless there is some other effect associated with shrinkage). However, if I now used a second layer of epoxy on top of the first, then I would reduce this dip by about 90% again, and I would expect to see an dip of about 0.02mm after that. In other words, for a given total depth of epoxy, you would do better to use it in two thin layers than one thick layer.

Does this also explain the effect that some people have seen where there is a noticeable shrinkage effect at rail/bridge joins - if you are not careful to get the bridge at the same height as the rail, then there will be a different amount of absolute shrinkage either side of the join and that might affect the resulting levels?

Jonathan's measured error curves are not quite in agreement with this principle, but his measurement technique is dependent both on rail height variation and rail twist, and once we are getting down to small numbers the measurement technique becomes important. However, it is interesting (but possibly coincidental) that his initial error was reduced from about +-0.3mm to about +-0.03mm. That's the kind of reduction that my thinking would have suggested although it doesn't prove anything due to, as I say, the different measurement technique.

If I had thought about it beforehand, then all this would have been blindingly obvious but then, I would not have expected quite as much shrinkage. Looks like epoxy is great, but it reduces rather than removes build alignment errors and the more accurately you can build the initial structure, the better the result after using epoxy. Shimming, on the other hand, should be able to take out arbitrary errors, although it's going to be much more difficult to measure and remove rail twist.

[EddyCurrent]

eHowever, if I now used a second layer of epoxy on top of the first, then I would reduce this dip by about 90% again, and I would expect to see an dip of about 0.02mm after that. In other words, for a given total depth of epoxy, you would do better to use it in two thin layers than one thick layer.

That's what the bloke in the video said, do a small pour first ; https://www.youtube.com/watch?v=NlifRFChReY

[Jonathan]

I'm happy to go through how I did my calculations if asked, but for the moment I'll skip directly to my conclusions.

I think your theory is worth exploring and (you guessed it) I'd like to confirm that your measurement method is sound since we don't want to be victims of correlation not implying causation.

Have you measured the shrinkage of your resin directly, since clearly if the resin shrinkage is far from 10% the rest of your analysis is potentially invalid (though not necessarily invalid, since it could still exist as a small effect masked by something else)? If you've not measured or got the data elsewhere, then perhaps pour some into a fairly thin tube, mark the level and when it sets measure the change, or think of a better method as I expect there will be one.

The west system resin datasheet says it 'does not shrink after curing (http://www.westsystem.com/ss/assets/Product-Data-PDFs/TDS%20105_209.pdf)', but does that mean it doesn't shrink during curing? I guess not else they'd surely specify. Adding thinners does increase the shrinkage, so one should be careful when selecting the resin to ensure it doesn't contain them as that option might seem attractive to reduce the viscosity.

Please could you elaborate on your measurement method to get the "height error from horizontal plane"? Did you add the feeler gauge under one end of the level until the level read zero, then note down the thickness of the gauge, or have I completely missed the point? If it's the former then the measurement is an angle from the horizontal plane (or strictly speaking the Earth's center of mass, but lets not worry about the earth curvature error), not height deviation without more careful interpretation of the readings.


Jonathan's measured error curves are not quite in agreement with this principle, but his measurement technique is dependent both on rail height variation and rail twist, and once we are getting down to small numbers the measurement technique becomes important.

I could have indicated from the surface plate to the resin, or from the rail to surface plate at two distances to separate the readings of linear and angular error ... but time was not on my side.


However, it is interesting (but possibly coincidental) that his initial error was reduced from about +-0.3mm to about +-0.03mm. That's the kind of reduction that my thinking would have suggested although it doesn't prove anything due to, as I say, the different measurement technique.

I'm not sure where you got the +-0.3mm from, but from the graph I posted in the thread it was more like +-0.5mm, then 0.3mm after the failed compensation method using a machined strip. However the graph I posted is a combination of the height and twist errors, so we can't actually conclude from this what the height error was.

We could gain confidence in your theory about the resin shrinkage by measuring if the height error follows the original profile, just with a smaller magnitude. My readings do not seem to follow the original profile, but as mentioned already the readings are a combination of the rotational and linear error, so we can't draw any conclusion from this.

Maybe I should try a simple test using my surface plate - create three channels, one directly on the surface plate with the surface plate horizontal (the 'control' experiment) and one with the surface plate tilted so the resin is significantly deeper at one end. Measure the linearity of both and see if there's a discernible difference between the samples.

[Sven]

Very nice to be able to read about this kind of process, I may need it in the future.

I've not yet read in to the particular shrinkage of epoxy but it seems to me that 10% is a number that is way too high, and that the measured gap is the result of something else.

I'll see if I can find any info on shrinkage and report back.

[Boyan Silyavski]

If you have read carefully my build, and implemented the technique i suggested that would not have happened. Epoxy shrinks and that is life.

Read from post #77 (http://www.mycncuk.com/threads/6619-Quite-an-Unusual-one?p=61550#post61550) on, or jump directly at the solution (http://www.mycncuk.com/threads/6619-Quite-an-Unusual-one/page13). i think i should write an epoxy guide and make it sticky. As i already paid the price to learn/~6kg of wasted expensive epoxy, 2 pours wasted for learning purposes :beaten:, so no need for others to repeat the mistakes.


Your epoxy shrunk at the bridge, cause the bridge shrunk lengthwise and sucked the epoxy from the center of the rail. Thats all.
I confirmed that in my build by calculating the given shrinkage of the epoxy, calculating the volume, length and so and it gave me as a result the exact shrinkage that happened.


One thing more. The glass transition temp of WS is 50C. So take care for direct sunlight in summer not to fall onto the epoxy, especially with heavy gantry. It will f^^ck up. I made some experiments and it becomes like a chewing gum quite fast. Faster than i liked.

[njhussey]

If you have read carefully my build, and implemented the technique i suggested that would not have happened. Epoxy shrinks and that is life.

Read from post #77 (http://www.mycncuk.com/threads/6619-Quite-an-Unusual-one?p=61550#post61550) on, or jump directly at the solution (http://www.mycncuk.com/threads/6619-Quite-an-Unusual-one/page13). i think i should write an epoxy guide and make it sticky. As i already paid the price to learn/~6kg of wasted expensive epoxy, 2 pours wasted for learning purposes :beaten:, so no need for others to repeat the mistakes.


Your epoxy shrunk at the bridge, cause the bridge shrunk lengthwise and sucked the epoxy from the center of the rail. Thats all.
I confirmed that in my build by calculating the given shrinkage of the epoxy, calculating the volume, length and so and it gave me as a result the exact shrinkage that happened.


One thing more. The glass transition temp of WS is 50C. So take care for direct sunlight in summer not to fall onto the epoxy, especially with heavy gantry. It will f^^ck up. I made some experiments and it becomes like a chewing gum quite fast. Faster than i liked.
50 degree C.....In the UK hahaha........not likely [emoji6]

[Neale]

I think your theory is worth exploring and (you guessed it) I'd like to confirm that your measurement method is sound since we don't want to be victims of correlation not implying causation.

I agree - it's all a hypothesis at the moment, and I'm still doing some measurements to get a bit more data. Silyavski's comments are interesting although I'm not sure that they agree with my data, and in one of his posts he comments on a 10% shrinkage (although I'm not sure which resin he was using at the time).


Have you measured the shrinkage of your resin directly, since clearly if the resin shrinkage is far from 10% the rest of your analysis is potentially invalid (though not necessarily invalid, since it could still exist as a small effect masked by something else)? If you've not measured or got the data elsewhere, then perhaps pour some into a fairly thin tube, mark the level and when it sets measure the change, or think of a better method as I expect there will be one.

I'm trying to work out the best way to do that. It's the only way to remove other complicating factors.


The west system resin datasheet says it 'does not shrink after curing (http://www.westsystem.com/ss/assets/Product-Data-PDFs/TDS%20105_209.pdf)', but does that mean it doesn't shrink during curing? I guess not else they'd surely specify. Adding thinners does increase the shrinkage, so one should be careful when selecting the resin to ensure it doesn't contain them as that option might seem attractive to reduce the viscosity.

I'm not using West System, and I have not found any shrinkage data for my resin.


Please could you elaborate on your measurement method to get the "height error from horizontal plane"? Did you add the feeler gauge under one end of the level until the level read zero, then note down the thickness of the gauge, or have I completely missed the point? If it's the former then the measurement is an angle from the horizontal plane (or strictly speaking the Earth's center of mass, but lets not worry about the earth curvature error), not height deviation without more careful interpretation of the readings.

I set two carriages on the profiled rail, so that I was not relying on the rail's surface. The carriages were set so that their centres were at the measurement points (every 200mm along the rail) and my 200mm level placed on them. I then measured the height difference between the two ends from a combination of feelers under one end (to bring the bubble "on scale") and the level's scale. I have checked the scale and as far as I can judge, the readings are reasonably accurate. The level has a nominal sensitivity of 1 div = 0.02mm/metre. I have remeasured my rail, working from both ends to check for systematic errors, and the two curves match pretty well so I'm reasonably happy that the technique does not introduce excessive cumulative errors. I shall post my data later; I have also tried to measure twist in the rail and I shall give that as well. I have also shimmed the rail but have not yet measured the finished result (it's so cold in the garage at the moment!)


Maybe I should try a simple test using my surface plate - create three channels, one directly on the surface plate with the surface plate horizontal (the 'control' experiment) and one with the surface plate tilted so the resin is significantly deeper at one end. Measure the linearity of both and see if there's a discernible difference between the samples.
Someone needs to do this! I had thought about a small clear plastic pot - I'll try both if I get the chance (and it's warm enough for the epoxy to set).

I can also try to get some data off my other X rail - I haven't examined that one yet.

[mitchejc]

Very interesting thread. I'm with Sylyavski on this one and I don't think shrinking is that much. Considering the viscosity of the epoxy, pouring a few thin layers is not going to improve things much and I believe your'e better off with one thick layer. As an extreme example start with an uneven surface and try to paint layers it until its perfectly flat... But please carry on testing as its the one way we'll really know. Its difficult to test though as there are so many factors for example some epoxy likes to be cured cured at higher temps e.g. 60 or 80 deg Celsius so temperature might also have a big effect on the actual results.

[mike os]

Has anyone

[mike os]

Has anyone considered the temperature expansion/contraction characteristics and it's effect (or its lack of) change with differing bed thickness? I know some epoxies can move quite a bit with relatively small temperature changes

[Neale]

Here are the "before and after" rail level measurements. That is, the results from the epoxy levelling (two curves, one measured going left to right and the other in the opposite direction, just to try to validate the measurement technique as obviously an error at one point will carry right through the remaining measurements). The third, flatter, curve is after shimming. Shims were calculated from the first pair of curves, and were to about the nearest "thou" as this was the thickness of the aluminium foil I used (with some 8 thou shimstock where it could be used). I could have used thinner foil but my wife wouldn't let me eat her Christmas chocolates which had thinner wrappers, even when I said that it was in the name of science and I wouldn't enjoy them...
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Jonathan - just for you!
To calculate shrinkage, based on my hypothesis that this caused the variation in depth, I had three unknowns. These were S1, S2, and Z. These are the loss in height at the shallow end, the loss in height at the centre (deepest epoxy), and the shrinkage ratio expressed as final height/original "as poured" height. I could measure the depth of the epoxy bed at both points, and the drop in level between them. It was then just a matter of throwing together a set of three simultaneous equations in these variables and solving for each in turn. Plugging the values back in to the original equations gave the right answers, so I am assuming that my maths is OK. Obviously, the underlying assumptions might not be, but that's what we are exploring here.

[Neale]

Has anyone considered the temperature expansion/contraction characteristics and it's effect (or its lack of) change with differing bed thickness? I know some epoxies can move quite a bit with relatively small temperature changes

Could be an issue, I suppose, but I can't check at present. It's consistently b****y cold in my garage at the moment!

And as an aside, I do have to say that I am chasing tiny "errors" here. My "with epoxy" flatness of about +-4 thou is well within any reasonably acceptable range for this class of machine. That's probably less than the manufacturing tolerance on thickness of any of the materials that I am likely to use on it. What started me on the current exercise is idly wondering why it wasn't "perfect" after using gravity and epoxy to set the surface.

What is concerning me a little at present is the amount of twist in the rail. From what I have seen with some preliminary measurements, that exceeds the HiWin figures for this kind of error. Although the HiWin catalogue does not give a "max twist" value directly, it can be inferred from the published figures for maximum height difference between pairs of rails, and I believe that the twist in my rail at present is maybe 3-4 times that. I'm still investigating...

[Boyan Silyavski]

Typical "non shrinkage epoxy" shrinkage is around 0.1% . I read that somewhere, don't ask me where, i read a lot of manuals and pdfs . 3000mmx0.1/100=3mm !!!! ,
even 1m has longitudinal shrinkage of at least 1mm, if the epoxy is very good like WS.

NON solvent epoxy means that the epoxy is 9x% something percent solid, not that its 100 % solid. And that small percentage is what f%%ks us.


-So avoid the bridge to suck from the rail, let the rail be longer so when it shrinks it sucks from the bridge and that the lowered area is not inside the machine frame. That simple.

-3mm minimum recommended epoxy thickness for the compression properties to be same as sheet specs, that's why the 5mm thickness.


-the variation of vertical shrinkage IMO is due to not perfect mix, bubles and not perfectly clean/acetone clean/ surface, small invisible gaps where the epoxy leaks but does not leak out. That simple.

[mekanik]

Hi Guys
Loitering as usual.
Spent the last half hour trying to find this http://www.moglice.com/
Might be worth a look if you have the time it was hiding in a build log i had saved
http://www.oneoceankayaks.com/madvac/machine_frame.htm
Regards
Mike

[mitchejc]

The accuracy you achieved after the shimming is phenomenal and I would be extremely happy if I can get mine remotely like that.
I can't imagine why there would be twist in the rail and I hope you figure it out as I'm likely going to run into the same issue.

[Sven]

On a side note:
So far i've only seen leveling systems utilizing "guttering" to let the epoxy settle.

Could it also be done using a plastic hose as a "hose level"?
Might be easier to set up.

[Neale]

Still haven't finished my second round of epoxy. All the results I gave earlier were from just one rail, and were looking good. Then I looked closely at the second rail...

Main problem was leakage through a couple of places where I had plug-welded through to attach an internal extra steel strip to increase the depth for tapping. There was clearly a slight weep which seriously distorted the surface, leaving a virtual step at one point which was just too difficult to shim. So, I tried to recover by adding more epoxy. One problem with the first rail was that the dam was made with draught excluder strip. This left the epoxy strip on the narrow side, the meniscus needed to be removed to get a flat surface, and it was difficult to do that without impinging into the area carrying the profiled rail. So, I decided to pour a second coat of epoxy on both sides. That meant plugging all the bolt holes (short lengths of dowel tapered using a pencil sharpener and tapped into the holes), and I used gaffer tape to build a dam around the outside of the steel box. I put it on so that it stuck up above the box section by about 8mm. I did this on both rails, even the one that I had shimmed earlier, just so that both sides were the same. Biggest problem was that you get a meniscus around the site of each plug which was difficult to remove without damaging the surface. Unfortunately, I didn't leave the epoxy long enough to really harden so when I bolted down the first profiled rail, it dented the surface which left grooves which were difficult to shim. In the end, I stripped all the epoxy off, and have started again. This epoxy has only been on for a couple of days so not hard enough yet to want to start drilling and bolting.

However, a few lessons learnt:

- Make the epoxy wide enough for your rails that you can grind or file back the meniscus without touching the area that will carry the rails. In fact, so that you are only removing the meniscus for cosmetic reasons.
- Gaffer tape makes a good dam/mould but watch out when you use a heat gun for agitating the surface/levelling and bubble removal. This heat gun technique is great but tends to soften the tape which sags a bit.
- I shall never drill before applying epoxy. Drill afterwards - epoxy drills really easily. If you find yourself in the position of having to epoxy an already-drilled surface (or ones with holes in for whatever reason) then I suggest that you don't try putting plugs in the holes as this just gives problems later. What does work is to cover the holes with small pieces of Sellotape. Leaves a much better surface, and the epoxy does not seem to attack the Sellotape.
- Epoxy doesn't stick that well to steel, even freshly wire-brushed and acetone-wiped steel. I was able to split it off by getting a chisel underneath it. Maybe that was just the epoxy I was using, though, but I won't be using it to make structural bonds on steel without more testing.
- Really, really, wait until the epoxy is hard before doing anything with it. Then wait a bit more, especially in this cold weather.
- (and this one is probably a bit more contentious) - consider very carefully if you really need a bridge. I'm not sure if it causes problems due to shrinkage or not - I don't think it does but others believe passionately that it does - but it is a pain to set up, block leaks, etc. What does a bridge buy you anyway? It cannot improve the "horizontalness" of an individual epoxy strip (but might make it worse). What it does, theoretically, do is make both rails the same height. Can you build a gantry that is so accurate that both "feet" are exactly flat, in the same plane, etc? Commercially, of course you can, but then you would probably be able to machine the tops of the rails anyway. I know that I am going to be shimming between the feet of my gantry and the X carriages, so I am happy to take up the odd mm or two height difference in the shimming. My latest epoxy layer hasn't used a bridge, and so far the epoxy surface is looking good when I look along it at reflections of the wall. I doubt if I'll be taking up more than the odd millimetre of height difference. Why make things difficult for no benefit?

I shall report back when this latest epoxy is fully cured and I have fitted the rails so that I can measure how well I've done. Or not...

[JAZZCNC]

- (and this one is probably a bit more contentious) - consider very carefully if you really need a bridge. I'm not sure if it causes problems due to shrinkage or not - I don't think it does but others believe passionately that it does - but it is a pain to set up, block leaks, etc. What does a bridge buy you anyway? It cannot improve the "horizontalness" of an individual epoxy strip (but might make it worse). What it does, theoretically, do is make both rails the same height. Can you build a gantry that is so accurate that both "feet" are exactly flat, in the same plane, etc? Commercially, of course you can, but then you would probably be able to machine the tops of the rails anyway. I know that I am going to be shimming between the feet of my gantry and the X carriages, so I am happy to take up the odd mm or two height difference in the shimming. My latest epoxy layer hasn't used a bridge, and so far the epoxy surface is looking good when I look along it at reflections of the wall. I doubt if I'll be taking up more than the odd millimetre of height difference. Why make things difficult for no benefit?

In which case don't bother with epoxy at all and buy straight edge to straighten and level the top rails. If the surface isn't pefectly flat it takes nothing but a file to knock off high spots and bit of epoxy filler to raise low spots. this can be down in the time it takes to setup and build good dams.

The whole point of the bridge is that it allows both rails to level on the same plane and to be honest if anyone can't setup a decent bridge or dam that doesn't leak I'd be quetioning there abilty to build the machine in first place.!

To me epoxy is ok but to be honest I only use it in certain cases like recently when I'm correcting someone else frame work. Rest of time I find it more work than it's worth and can reach the same results or better quicker using straight edge and shimming. But for those without precision straight edges then realise it's a quick and easy method if done right. (thou you'll still need a straight edge at some point so don't bother and buy straight edge is my thinking. .Lol)

[mitchejc]

- (and this one is probably a bit more contentious) - consider very carefully if you really need a bridge. I'm not sure if it causes problems due to shrinkage or not - I don't think it does but ...

I totally agree that the benefits of a bridge between the X sides does not justify the pain. Like you said you can easily make up that small height difference when you mate your gantry and x base blocks with epoxy putty which one has to do anyway to ensure one doesn't put stress on the bearings when bolting the gantry to the x bases. I've done mine without a bridge and I did not have any issues or weird side effects afterwards with setting up my gantry, so go for it. Others might have had a different experience but my epoxy does not create a perfectly flat surface. The epoxy scrapes VERY nicely so I used a 260mm long planer/thicknesser blade to scrape it to spec.
I guess not needing epoxy casting is first prize and in hind sight, I'd be very surprised if the end result is more more accurate than using the filing and shimming process as described by Jazz.

[JAZZCNC]

I guess not needing epoxy casting is first prize and in hind sight, I'd be very surprised if the end result is more more accurate than using the filing and shimming process as described by Jazz.

It's not more accurate it's actually much less accurate if scraping/shimming is done correctly but it is much easier and less time consuming for for those not equiped or experienced.

Regards not using a bridge can I ask how you know there is no difference in height between one side and the other.? Ie both rails on same plane.?

[gavztheouch]

It's not more accurate it's actually much less accurate if scraping/shimming is done correctly but it is much easier and less time consuming for for those not equiped or experienced.

Regards not using a bridge can I ask how you know there is no difference in height between one side and the other.? Ie both rails on same plane.?

epoxy method is nice because it makes sure your rails are on the same plane. How do you achieve this with a straight edge and shimming?

[Boyan Silyavski]

I liked the epoxy the first time on the 1000x400 machine. i hated it on the 3000x1300 , untill i figured my mistakes and made it right. The way as i see it if i have done correctly this one, i will stop using epoxy in the future when i am building smaller machines that fit inside that one.



I still don't see how sb will shim properly 3000x1300 machine. I mean to make try to make the machine not relatively straight but absolutely straight, which are 2 very different things. Though for 95% of the people relatively straight is more than straight enough.

By relatively straight i mean long rails not perfectly on 1 plane, one rail as a guide and the other straightened via the carriage, and so on. After the table is surfaced it will not show unless you have 500mm Z axis and are doing 500mm high details. If you get what i mean.

I spend a lot of time aligning and mounting my rails and even with all in one plane, even with a helper. Man, trying to make all absolutely straight is a big waste of time. It goes so slow. And you have to triple check everything. If sth not right do all again. Holding carefully 15kg straight edge does not speed the process up, i just can not imagine what will be if the rails were not in one plane. :dejection:

I know sb. could argue here but let me tell you something. Remember, i am speaking of trying to make an absolutely straight machine here. On a machine with 1350mm wide working area the rails are 1800mm separated. Using 2000mm square edge across is extremely difficult to square the second rail to the first. Why? Cause you move one side 2mm and the precision square still shows its square. You have to scratch the straight edge with precision square and judge by the friction if its square or not. There is no other way. So yeah, tell me now if at the same moment you have to check if the rail is not wavy, twisted and so on, and what happens if the rail itself is not straight from transport so you have to push and pull here and there while screwing. You need to grow some more hands. Now another thing. Even 1 tiny dust below the rail and it shows. So it slowed even further all.

So my suggestion is to speak of relative or absolute straightness when speaking of how it is done, cause its different. But as i said, my guess is that people most of the time are meaning in their heads absolute straightness and at most achieving in real life a relative one :hysterical:

Dean again i agree with you, in a way :semi-twins:. Absolute straightness /or a try at it/ in a DIY CNC is needed only if you make aluminum molds, surface aluminum machine beds and rails and generally intend serious production of aluminum pieces. Man i am not preaching OTT. But if sb spend considerate amount on BOB, Steel, motors, rails and so, he should at least give a try for an absolute straightness. Hence the bloody epoxy.

[mitchejc]

Regards not using a bridge can I ask how you know there is no difference in height between one side and the other.? Ie both rails on same plane.?

Jazz, the way I see it the X rails don't have to be on the same horizontal plane as long as the two planes are parallel ie. if rail X1 is 2mm higher than X2 it must be 2mm higher everywhere along the length. There's probably other ways to do it but I epoxy casted a T shape reference surface on my base and used that to set up my Y and Z. The machine in the extreme example below will cut perfectly well as long as the y rails are parallel to the ref surface who's horizontal plane is parallel to the two x-planes. Mine, does not look like this as the x height difference was minimal:-) I used little skrew adjusters and then epoxy putty to shim my gantry bottom parallel to the ref surface and gantry front perpendicular to the ref surface and also used the ref surface to set up my Y rails and Z. Casting the ref surface does add a bit of extra work but once its there its very easy to set up Y and Z as opposed to some other methods I've seen.


http://www.mycncuk.com/attachment.php?attachmentid=14566&stc=1

[mitchejc]

not relatively straight but absolutely straight

Silyavski, concerning rails and things there is no such a thing as absolutely straight. If it appears to be absolutely straight you are just not measuring it fine enough. Just getting back at you for saying my fans suck :cheerful:

Apologies to the OP for the digression.

[Neale]

Thanks for the picture, Mitchejc - that's exactly what I was meaning. X1 and X2 may be "level" in the sense of horizontal to the limits you can achieve with self-levelling epoxy, but they do not have to be in the same plane, just parallel. It's the same error and corrected the same way as not having the feet of the gantry exactly co-planar. It's not ideal, but once set up, your friends will never know the difference...

I have to agree that epoxy is a second-best. If we could use self-hardening water, I might believe that the surface would be ideal, but even low-viscosity epoxy doesn't run that well, and I suspect that you also get surface imperfections because of internal stresses caused by shrinkage. If I had a surface plate 1.8x1m, I would consider scraping (proper engineers' scrapers and everything, I've used them before) the top of the rails to it. In my case, I was looking to take out a dip in the 100x50 box sections of something around 1.5mm. I don't know why it was that bad, whether the box section was warped when I bought it or if it is welding distortion or what, but it would need quite a lot of filler and/or filing to get that flat to acceptable limits, and it just ain't that easy to do. As pointed out, even if you could use a straight edge to get the top level along its length, measuring twist is really difficult even though the profile rail manufacturer's specs are pretty tight and you need to get it right (or at least consistent along the length of rail).

[JAZZCNC]

I still don't see how sb will shim properly 3000x1300 machine. I mean to make try to make the machine not relatively straight but absolutely straight, which are 2 very different things. Though for 95% of the people relatively straight is more than straight enough.

Your fooling your self if you think you can build and more importantly measure to Absolute levels. Every DIY build is a compromise between accurecy and engineering abilty.


Jazz, the way I see it the X rails don't have to be on the same horizontal plane as long as the two planes are parallel ie. if rail X1 is 2mm higher than X2 it must be 2mm higher everywhere along the length. There's probably other ways to do it but I epoxy casted a T shape reference surface on my base and used that to set up my Y and Z. The machine in the extreme example below will cut perfectly well as long as the y rails are parallel to the ref surface who's horizontal plane is parallel to the two x-planes.

Agree completely but again your only has accurate as your reference surface and abilty to measure. Not every one as large granite surface table for reference surface to work or cast from and without one then how sure are you your reference surface is accurate.?



If I had a surface plate 1.8x1m, I would consider scraping (proper engineers' scrapers and everything, I've used them before) the top of the rails to it. In my case, I was looking to take out a dip in the 100x50 box sections of something around 1.5mm. I don't know why it was that bad, whether the box section was warped when I bought it or if it is welding distortion or what, but it would need quite a lot of filler and/or filing to get that flat to acceptable limits, and it just ain't that easy to do. As pointed out, even if you could use a straight edge to get the top level along its length, measuring twist is really difficult even though the profile rail manufacturer's specs are pretty tight and you need to get it right (or at least consistent along the length of rail).

It's all about having the right tools whether it's hard or not. With Precision straight edges and Engineers levels it aint that difficult. But here lies the problem becasue at DIY level 99% don't have or need these tools and the epoxy method with bridge makes it possible for less tooled up DIYers to achieve acceptable levels of accurecy for gantry router style machines.

The key word here being ROUTER. . Remember these are mostly Gantry based router machines being spoke about and the nature of the beast dictates lower accurecy is acceptable and high precision accurecy unobtainable.!! . . . .Again Horses for courses and use which ever method gets the job done for you in the easiest way possible.!

[Rich]

Have you considered whether the fault lies with poorly mixed resin? The cure is a polymerisation. If the relevant components aren't available in sufficient quantities, the density of the film may change, leading to variation in final thickness?

Epoxy resin tends to be quite sensitive and there's little mention of preparation in this thread.

Using a good set of scales will ensure the right amount of resin and hardener is used. Really important if you want to resin to perform per manufacturers specifications e.g. hardness

Mixing. Spend at least five minutes mixing before use. Hand mixing is fine, an electric mixer is easier, but a slow speed. Avoid mixing in air. Once you have mixed for a minute, use a pop stick to ensure the resin sitting on the side and in the crease of the cup is integrated properly. Mix for the remaining four minutes. Once the batch is mixed, poor into a separate cup - leaving a little behind, so as to avoid any un-mixed resin transferring across.

The surface to be coated needs to be clean and dry.

The video was helpful in some respects. Personally, I wouldn't put a heat gun near epoxy without wearing a mask - air bubbles or no. But he's right epoxy loves heat and it does affect the viscosity of the poured resin. Personally, I'd lift the temperature of the resin prior to mixing using a water bath, especially here in the UK. I'd also be more interested in ensuring the ambient temperature of the room remained constant - especially in a hot climate.

I understand the target thickness for the film is 3-5mm. There's no reason why this need to be done is one pour: http://www.westsystem.com/ss/epoxy-chemistry/ A second layer can be applied once the first layer has started to gel, sufficiently. This might well be the best approach, assuming the underlying cause is human error

I'm not entirely certain what steps are taken after the film has been applied, but if the variation remains say 0.3mm i.e. human error is not a factor, could a high viscosity resin/compound then not be used to seat the rail? I believe that what is taking place here? http://www.moglice.com/ . You'd need to wait around a week before seating the rail. Ambient cure epoxies take a while to reach a state of final cure, which could be a problem, as you don't want an ultra thin layer of epoxy being exposed to pressure, when not chemically bonded to the layer below .... all my epoxies are heat cure, so I'm not in a position to run any tests. So lets hope its human error and applying two layers to create the desired thickness produces a lower error rate.

Oh yes. Vinegar is a good solvent for any split epoxy.

Personally, for this job, I'd been thinking about urethanes - but I'm not any way near needing to do this yet.

[Boyan Silyavski]

Mixing definitely is not the error if you mix the epoxy 10 minutes. Though i agree that it could be if not careful.

I believe i showed all already how to arrange and pour epoxy properly on even very big table, + saving 1 liter mixture at least on doing it with one bridge only. i hope my experiments and waste of money was not a waste, so people repeat the same mistakes over and over again, just because they want to do it their way or reinvent the hot water.

We could speak and speak, but - the errors are the following below. Only one of them or a mixture of them. Nothing more, nothing less.

1. Epoxy:
-poor choice / epoxy not fit for casting/
-shrinkage /not pure epoxy, cheap epoxy/
-cast thickness -ideal 5mm, no less than 3mm


2. Temperature:
-less than 15C or max 35C, ideal 22C
-differential between material temperature / heating the room shortly before, bringing the epoxy from other room/

2.Mixing:
-not weighting precisely the mix parts
-too much air in mix
-mixing less than 7-10 minutes
-not changing the mixing bowl with new, just before pouring

3. Surface preparation
-not cleaning the surface with acetone prior to pouring
-dust on the surface or hidden at the corners

4. Dams
-varying distance between dams on same rail
-too flexible dams
-dams from different material at different places
-hidden leaks between dam and material that don't show outside leak -not impregnating and check beforehand with thin epoxy layer for leaks
-dam leaking or absorption due to wrong dam material


5.Bridge
-not positioning it right so when it shrinks it sucks from channel
-not making extra long dam structure at the long rails
-not making bridge and dam extensions strong enough
-wrong bridge and extensions material,

6. Heating/degassing
-heating too much/too slow pass with the torch/
-making more than 2 separate passes /leads to orange peel/
-heating from different angle,not trying to be 90 degree with the torch
-heating too much the dams if they are from plastic
-accidentally heating the bridge more than the epoxy mixture

7. Drying
-dust when drying
-checking with finger if the epoxy is dry, during the first 24h
-laying the rails on top during the first 3 days to check how it looks
-mounting before a week has passed from pour

8.More
-not checking for dust particles that integrated during drying and scraping them with the straight edge
-not cleaning properly the rails and epoxy from dust before mounting, seat with the edges and scrape when laying down so no dust gets trapped
-heating the epoxy during drilling
-not chamfering the holes properly to clean the raised epoxy
-knocking the epoxy when dropping something or checking with the rails, and so making invisible raised points

9.later
Exposing the machine to >50C/ direct sun when outside temp is >25C/ will lead to problems.


Thats all folks. Do it properly and you will have 0.01 precision. Do it right and you will have great machine. Miss one point and you will have woodworking machine. Miss 2 and you will have a problem. Though of course people could lie to themselves and believe they have done it ok.

[JAZZCNC]

Thats all folks. Do it properly and you will have 0.01 precision. Though of course people could lie to themselves and believe they have done it ok.

Sorry Boyan but who's lieing to them self's if they believe they can measure to 0.01mm accurecy over 3000mm length.!!! . . . . . Yes Epoxy method works OK and easy when done correctly but anyone is fooling them selfs if they think there going to get accurecy down to the Hundreth's MM's over such length and width.!!

Thou as they say in Yorkshire " Proof is in eating the pudding" so when your machine is finished let us know if your machine can surface two faces parallel to each other across it's full length & Width then surfaces hold ONE hundreth millimeter parallelism over the whole length.? . . . Then I'll be impressed and Don my Flat Cap to epoxy and You Sir.!

[Boyan Silyavski]

Its relatively speaking. I did not mean to brag or mislead, just to encourage and lay down the points that should be followed to the letter, if one wants to achieve what could be achieved at home.

Yes Dean, its more like a wishful thinking. Of course it could not be measured, especially at home. I agree its not real 0.01mm. Maybe even not real 0.05mm at some places. But may be it is between 0.01 and 0.05mm if lucky and done right/. I was able to discover bigger than 0.05mm gaps using the edge and strong led torch.

Lets say i am happy when with the straight edge i could not find a spot where it did not look perfect and tight fit to the edge. Thats my criteria for straightness for my machine. Obviously on a 3000mm travel, that's something, when done right and at home.

Having in mind that the straight edge itself is not so straight over 3000mm , table below, that on paper it should be supported/handled at a special length for the measurement to be right i would say there is no way that something could be proven right or not.

That means though that there is still a small chance in a million that in fact is that straight. :joker:. Who knows, when its not measurable. :hysterical:


So i say, better do things right with the idea that all must be perfect. Yeah the result may not be. But what would happen if one even does not even strive to do it right.



http://www.mycncuk.com/attachment.php?attachmentid=14886&stc=1

[Rich]

Thanks Silyavski, its good to have all the detail laid out like that.

When thinking about the issue last night, I had in mind UK conditions and the tendency, recorded within various logs, to complete this task at below 25oC i.e. circa 10oC. This is relevant because as a general rule of thumb, a 5 degree F increase in cure temperature will half the time taken to cure, which is a thought I'd like to carry forward.

Per Jonathan's data, the suggestion must be that even with careful construction and preparation, the process retains a relatively high error rate, when compared to the required outcome. My addition is to suggest that the impact of the error rate, regardless of cause, could be halved by taking a two pour approach. I think that's relatively sound logic. But that not good enough.

However, as per the original posts #1, it took 72 hours to reach a state whereby it was possible to mark the epoxy using a finger nail i.e. the epoxy was still in a very plastic state at this time. So I am thinking, is this not the time to be thinking about mounting the rail?

The sort of procedure I have in mind is detailed below, but then I don't know how long it takes to mount the rail accurately? How much tinker time is needed?

Broad brush, the process would be as follows:

- Set up a bench test for the epoxy you are using. Dam an off-cut from the material used to make the supporting axis, circa 30cm in length?

- Before testing the epoxy, measure the ambient temperature, it needs to be below the manufacturers recommended cure temp, let say 15oC instead of 25oC. This provides for a much long gel and cure time.

- Mix and pour. One layer or two, depending on your view.

- Measure the hardness of the epoxy at regular intervals during the cure. A cure schedule can be drawn up based on the manufacturer specs in any event. Once it becomes evident that a thumb print can be made, start measuring the hardness of the cure by dropping a ball bearing from the same height and recording the difference in the diameter of the depression made.

- At a point to be determined by the dropping of the ball bearing i.e. while the epoxy is still relatively plastic, seat the rail using pre-drilled placement holes.

- There is where there is a balance to be struck, or not, depending on tinker time and ambient temperature. The rail needs to be seated on epoxy that is able to resist the the weight of the rail, but unable to resist seating of the rail when lightly bolted into place i.e. such that there is insufficient upward force to cause a deflection in the rail at the mid-point, between the two bolts.

Clearly it would help to run this experiment a few times. Removing a test sample isn't an issue.

Silyavski,
Like you clearly suggest, the right epoxy system is key. I would be concerned about using the West System if the ambient temperature is above 25 degrees C. Mixing - don't just stir the components together, mix the top into the bottom. Acetone will affect the chemistry of the resin system, so clean the frame well before the dam is constructed. Personally, I would do any final wipe using IPA. Heating/Degassing ... don't mix bubbles in. I wouldn't put a heat gun near epoxy, random application of heat? Use a brush and wet out the steel - like they did in the video. If you must, use a hair dryer set at min heat until you have a level. Heat the resin as a whole should you need to lower its viscosity prior to pouring. A water bath is the safest method - just be sure to dry the cup, as water and liquid epoxy need to be kept apart. Has anyone used a syringe to transfer the epoxy into the dam - 100ml every 40 cm or so?

[Boyan Silyavski]

Rich,

its proven that's its better to drill when epoxy is dry, not before pouring it and then messing with masking the holes.

The epoxy should be same temperature as the table to avoid shrinkage. yes you de-gass it by slightly heating it, but you pass with the torch very fast and as i said if you heat it further here by mistake, you will end with orange peel surface .

i dont insist on that, but its my feeling that the epoxy should be same temp. I took care of that and it worked. Why waste 100euro pour, just to see if it can be done as you say. :listening_headphone

[JAZZCNC]

Yes Dean, its more like a wishful thinking. Of course it could not be measured, especially at home. I agree its not real 0.01mm. Maybe even not real 0.05mm at some places. But may be it is between 0.01 and 0.05mm if lucky and done right/. I was able to discover bigger than 0.05mm gaps using the edge and strong led torch.

Boyan I agree that in all aspects of building that 100% should be put into every aspect of building but one of my pet hates is seeing boast's or claims regards accurecy or torque/power etc like Some calculators offer that can't or haven't been proven. I feel it's misleading and while possible to achieve it's Very very difficult in reality to achieve and even harder to verify. This can and does cause the less equiped or able to over expect results leading to dissapointment.

IMO it's much better to give the details of how it's done and leave out any claims of accurecy unless can be verified to avoid dissapointment and instead show results of your labour with work produced.

Don't take me wrong here i'm not taking anything anyway from your build and I'm quite sure your machine will give very good accurecy and results. But to me the whole point is what gets spit out the other end, so IMO build to the best of ones abilty and be happy in the knowledge that what comes off the cutter is the best it can be given each persons Skills/equipment.! . . . . THE POINT. . . . Don't get hung up on pointless details that can't be proven or seen.!!!

[njhussey]

Thanks Silyavski, its good to have all the detail laid out like that.

When thinking about the issue last night, I had in mind UK conditions and the tendency, recorded within various logs, to complete this task at below 25oC i.e. circa 10oC. This is relevant because as a general rule of thumb, a 5 degree F increase in cure temperature will half the time taken to cure, which is a thought I'd like to carry forward.

Per Jonathan's data, the suggestion must be that even with careful construction and preparation, the process retains a relatively high error rate, when compared to the required outcome. My addition is to suggest that the impact of the error rate, regardless of cause, could be halved by taking a two pour approach. I think that's relatively sound logic. But that not good enough.

However, as per the original posts #1, it took 72 hours to reach a state whereby it was possible to mark the epoxy using a finger nail i.e. the epoxy was still in a very plastic state at this time. So I am thinking, is this not the time to be thinking about mounting the rail?

The sort of procedure I have in mind is detailed below, but then I don't know how long it takes to mount the rail accurately? How much tinker time is needed?

Broad brush, the process would be as follows:

- Set up a bench test for the epoxy you are using. Dam an off-cut from the material used to make the supporting axis, circa 30cm in length?

- Before testing the epoxy, measure the ambient temperature, it needs to be below the manufacturers recommended cure temp, let say 15oC instead of 25oC. This provides for a much long gel and cure time.

- Mix and pour. One layer or two, depending on your view.

- Measure the hardness of the epoxy at regular intervals during the cure. A cure schedule can be drawn up based on the manufacturer specs in any event. Once it becomes evident that a thunb print can be made, start measuring the hardness of the cure by dropping a ball bearing from the same height and recording the difference in the diameter of the depression made.

- At a point to be determined by the dropping of the ball bearing i.e. while the epoxy is still relatively plastic, seat the rail using pre-drilled placement holes.

- There is where there is a balance to be struck, or not, depending on tinker time and ambient temperature. The rail needs to be seated on epoxy that is able to resist the the weight of the rail, but unable to resist seating of the rail when lightly bolted into place i.e. such that there is insufficient upward force to cause a deflection in the rail at the mid-point, between the two bolts.

Clearly it would help to run this experiment a few times. Removing a test sample isn't an issue.

Silyavski,
Like you clearly suggest, the right epoxy system is key. I would be concerned about using the West System if the ambient temperature is above 25 degrees C. Mixing - don't just stir the components together, mix the top into the bottom. Acetone will affect the chemistry of the resin system, so clean the frame well before the dam is constructed. Personally, I would do any final wipe using IPA. Heating/Degassing ... don't mix bubbles in. I wouldn't put a heat gun near epoxy, random application of heat? Use a brush and wet out the steel - like they did in the video. If you must, use a hair dryer set at min heat until you have a level. Heat the resin as a whole should you need to lower its viscosity prior to pouring. A water bath is the safest method - just be sure to dry the cup, as water and liquid epoxy need to be kept apart. Has anyone used a syringe to transfer the epoxy into the dam - 100ml every 40 cm or so?
Rich, you need to leave the epoxy until it is totally set. If you bolt the rails to it before its totally set they'll sink into it. Eddycurrent had just this thing happen to him, he corrected it by filling the marks/dents with more epoxy.

[Rich]

I'm advocating a bench test in advance of pouring! Surely that saves money Sil?

I would leave the bolts in and if they were a little resistant, I'd heat gently using a soldering iron to release them. That's if I hadn't applied mold release.

Shrinkage is a post cure issue ... you might be seeing a change in viscosity due to temperature disparity between the resin and the table, which is affecting flow. The resin will quickly adopt the temperature of the table in any event, hence the suggest to paint on a thin film in advance of a pour - but in reality the impact on flow will be negligible.

Syringes, reminds me of these: http://uk.rs-online.com/web/p/epoxy-mixer-nozzles/0503385/ If you want belt and braces on the mix.

The resins I use are heat cure epoxies, so I don't have anything suitable for running a test. Once I've sold a few more things on Ebay, I look at finding a suitable resin system for the job.

Neil,
Hence the need to run a bench test in advance and track the behaviour of the epoxy you have chosen.

[Clive S]

I would be hesitant of leaving the bolts in as you will get miscues around the bolts like you will get at the edges of the moat. I used West System very slow cure 10 - 20 hours. After I had a long conversation with them on the phone they suggested that I flash the surface with a hot air gun (just a very quick flash) 5mm one pour. ..Clive

[mekanik]

Hi Guys
Have been following the progress of this thread and think there might some advantage in using trace heating cable on the bed to provide a stable temperature prior to resin pour, bed can be uniformly heated then knock off the power and let the bed cool to the desire temperature and do the pour.
Regards
Mike

[njhussey]

Well I'll be watching with interest to see the results of all this...

[Rich]

Clive - a soldering iron to the head of the bolt should stop that. Apply just enough heat to let it dissipate from the thread.

Cheers Mike, like you suggest, if you are going to apply heat to lower the viscosity of the resin, it needs to be applied uniformly. A heat gun is a little too intense and random IMHO. Adding an aluminium plate to the nozzle would certainly help the situation - a more consistent heat over a wider area.

Heating the frame with trace heating ... that's a lot of metal? Have you seen this thread: http://www.mycncuk.com/threads/6565-Ready-Steady-Eddy/page18 , photograph 6, you'll see a piece of flat bar below the film. There's no reason why this bar couldn't be used as a heat shield - held at a prescribed height above the dam (pre-drilled holes and placed back below, once the film had set). Ideally, it would be a little wider, but this approach would put the heat gun back on the menu, switch to full power with little risk of over-heating the surface ) I'd be inclined to test that last comment, especially as the thread of the bolt holding the bar is sitting in epoxy. If you are happy to keep waving the heat gun around in a consistent fashion, it would have the desired effect - reducing the viscosity of the resin and if you are patient and consistent i.e feet per second, you'd be well on you way towards curing the epoxy within specs. This assumes a thermometer, temperature gauge or such like between the flat bar and dam and the bolts don't become the focus of any heat build up.

Anyway - thanks for entertaining these ideas. If someone could let me know how much tinker time should be allowed for setting up the rail, it would help.

[gavztheouch]

I would be hesitant of leaving the bolts in as you will get miscues around the bolts like you will get at the edges of the moat. I used West System very slow cure 10 - 20 hours. After I had a long conversation with them on the phone they suggested that I flash the surface with a hot air gun (just a very quick flash) 5mm one pour. ..Clive

Clive I have some West systems slow cure coming on Monday, after the pour when should I flash the surface? Straight away? Is a hair dryer hot enough or do I need a proper industrial hot gun?

Cheers

[njhussey]

Clive I have some West systems slow cure coming on Monday, after the pour when should I flash the surface? Straight away? Is a hair dryer hot enough or do I need a proper industrial hot gun?

Cheers
Gav, a hair dryer will just blow the epoxy and splash it everywhere....i believe (I didn't do it myself as I didn't have many bubbles) the time to do it is when you're happy that you've got the epoxy evenly spread out and are just about to leave it to cure but I'm sure Clive will tell you when he did it.

[Clive S]

http://www.mycncuk.com/attachment.php?attachmentid=14890&stc=1Ok This has all been said before. The system I used is this http://www.westsystem.com/ss/209-extra-slow-hardener/ this is the pdf. http://www.westsystem.com/ss/assets/Product-Data-PDFs/TDS%20105_209.pdf
.
It is very important to measure and mix well. it is important to make the moat water tight as any small leaks will spoil the job. I used a thin bead of silicone all round the inside edge. Just make sure that the frame is least at about 18C .
.
Mix the epoxy with a flat paddle ie not a round dowel and mix well slowly so as not to introduce air into the mix then let it settle for a couple of minutes. If you have another prepared container with a hole near the bottom about 6-8mm with some tape over it you can then pour the epoxy into the prepared container.
.
Then take the tape off the hole and let the epoxy pour from the hole into the moat. (this will get rid of most of the air as bubbles rise and you are pouring from the bottom)
http://www.mycncuk.com/attachment.php?attachmentid=14888&stc=1http://www.mycncuk.com/attachment.php?attachmentid=14889&stc=1
.

Don't just pour all the epoxy in one place but try and get it even all the way round. Then if you see any big bubbles you can just flash them with the hot air gun they instantly disappear. (you are not trying to heat the epoxy up it is a quick flash)
.
The epoxy is almost like water and will flow very easy.
.
Rich There is no way a soldering iron will stop the surface tension miscues thing from happening all around the edges of the moat AND around any bolts you have put in.
.
When the epoxy has cured at least a week then remove the moat sides etc and with a rasp bastard file carefully remove the miscues. If you are using 20mm rails you want the moat at least 40mm wide (mine was 55mm)

I used two dams from one rail to the other and was more than happy with the result.
.
This has all been done to death and is not rocket science I think in a hot country you may have to be a bit more careful. The epoxy may feel hard to touch but DON'T play with it until at least 7 Days have past and has been said already make sure that the base is clean and oil free. You can rub some oil around the inside of the moat edges to stop the epoxy sticking to the sides (make sure it is sealed first though). ..Clive

[JAZZCNC]

Clives spot on and speaks from experience so anyone going to do this would be advised to listen. Esp about the time to leave and longer the better I find.
It's very easy to get caught out thinking it's cured fully when it's not and then get sinkage, I've had it happen to me recently after leaving nearly a week and should have known better but was rushing. so don't think it's a rookie mistake because you will get caught out if you try to rush.!

One way good way to test if fully hardened is to make separate test piece same width about 12" and pour to same depth. (the moat will work for testing) Then pour at same time and leave.
Then when you think it's cured check the test piece by bending, if it just bends and doesn't snap then your not cured enough, if it snaps then your ready.

[Clive S]

Then when you think it's cured check the test piece by bending, if it just bends and doesn't snap then your not cured enough, if it snaps then your ready. Yes I forgot that bit:yahoo: .. Clive

[matthewb]

I wonder if anyone has tried polyurethane casting resins instead of epoxy for levelling?

The stuff i have used in the past ( for casting not machine levelling) has the viscosity of milk and is designed to run and fill all the voids in a casting, i would imagine it would be better than most of the epoxy resins i have come across.

Its tough too and will take fillers and reinforcements if you want to use them.

http://www.benam.co.uk/products/plastic/

just a thought...

[Rich]

Thanks Clive, I will go back and edit, so it's clear that I am talking about the threaded bolts. The residual meniscus would be of a nominal thickness using this method and subject to removal once the drilled hole was opened out.

These guys might be worth a shout: epoxies start at page 58: http://www.swiss-composite.ch/scs4/html/index.shtml?lang=en (selling on behalf of: http://www.r-g.de/en/ ) I've never had cause to deal with them directly, but they are known to have a good reputation. Supplier to light aircraft industry, so quality is a priority.

Using the west system 105/209 as a point of reference, viscosity of the mixed resin @ 22oC is 650mPas. This figure will increase as the temperature decreases, so the resin will become more viscous, the lower the temperature gets. Minimum recommended temperature for the 209 is 18oC. Physical properties once cured are really important, so its good to have this datasheet as a reference point.

Possible alternatives:

- low viscosity resin system 100 mPas @25oC, cures at 10oC
- low viscosity resin system 250 mPas @25oC, cures at 15oC

There are some other low viscosity resin systems in there, if your ambient is higher.

Jazz, you're waiting 7 days? You're not adding any heat, not even ensuring a consistent 15oC?

[JAZZCNC]

Jazz, you're waiting 7 days? You're not adding any heat, not even ensuring a consistent 15oC?

How do you get that I never added any heat or kept a consistant Temp just from me saying waited nearly a week before fitting rails.?? . . You know what they say about Assumption.!!
My workshop is fully heated and Temp controlled with a Thermostat. The frame was slowly brought to room temp of approx 17deg over 3 or 4 days before applying epoxy and then workshop was kept at this temp for constant 3 days 24/7 afterwards then rails fitted after 6 days of curing.
This was using West systems 206 Slow hardener not 209 but still it caught me out, which I should have known better after doing several machines with epoxy.

[Rich]

From experience I know my elevated cure resin will harden in cold well, just add time. Excluding the 205 hardener, a workable cure should be achieved within 2.5 days (72oF cure is 15 hours max, 67oF equates to 30 hours, 62oF should be 60 hours). They quote 'thin film'. It tends to be 1mm or so. Thicker films, shorter time periods. I guess you must have been unlucky, or the hardener is getting old.

Matthewb,
I agree, polyurethane has potential with some additional benefits, including vibration dampening. I had a quick look at the website you posted. There were some reasonable numbers, attractive numbers on shrinkage, however, they tend to require elevated post cure. Quite expensive in my opinion. Have you thought of looking to the industrial floor coating industry - they might entertain a few free samples. Help you get your eye in before you pour.

Just noticed this website: http://www.resins-online.com/ I'd contact the underlying manufacturer for clarifications.

[Boyan Silyavski]

How do you get that I never added any heat or kept a consistant Temp just from me saying waited nearly a week before fitting rails.?? . . You know what they say about Assumption.!!
My workshop is fully heated and Temp controlled with a Thermostat. The frame was slowly brought to room temp of approx 17deg over 3 or 4 days before applying epoxy and then workshop was kept at this temp for constant 3 days 24/7 afterwards then rails fitted after 6 days of curing.
This was using West systems 206 Slow hardener not 209 but still it caught me out, which I should have known better after doing several machines with epoxy.

Thats what i meant before, but could not explain it better. Machine,epoxy and room should be same temperature from the moment of pouring to the moment ready to mounting.

I have done some experiments and epoxy will even cure at 5C though not advisable.

[JAZZCNC]

Lets be getting real here.? Epoxy method isn't rocket science and doesn't need to be made so.!! . . .It's just a matter of using correct Resin/hardner mixing it correctly and applying in clean enviroment at sensible tempreture with-in Manufacturers recommendations. . . THEN . . . Leaving alone until it cures FULLY.

By far the Hardest part for most is being patient enough to leave for couple of weeks but it really is best if your unsure because if rails are bolted on and they Sink it's all been for nothing and correcting is hassle.!

Silyavski as highlighted some good points and made sensible suggestions which for anyone building a Large machine with lots oof expensive epoxy would do well to follow but for smaller machines where Epoxy settles quicker and easier to handle then it really is quite simple if some common sense is applied.!

Clean, Warm, Dry with leak free dams and it's a doddle. .:cower:

[Rich]

Jazz, so you're saying the epoxy method, as described by Clive and Silyavski is the best way to go because it achieves what level of accuracy?

[Boyan Silyavski]

Jazz, so you're saying the epoxy method, as described by Clive and Silyavski is the best way to go because it achieves what level of accuracy?

Let me respond instead.

It achieves the level of accuracy of your straight edge + your intention of accuracy.

You need a straight edge that should be at least as long as your machine is wide, to check the result and later square the gantry. Your intention of accuracy will help you see small mistakes if any and using shimming and checking against the edge will help the desired accuracy. Anyway you will need the edge to mount the rails straight in the other direction. The more accurate you want it to be, the more you will check and adjust and generally the more time it would take you.

For an example i did 3 separate pours of epoxy on my 3m long rails, when happy with the epoxy i mounted and dismounted 2 times the left rail and 4 -5 times the right one until i was happy. It took a week with helper, only adjusting the rails. The only reason to do that was because i will use that machine to surface other smaller machines and gantries in it and not mess in the future with epoxy :black_eyed: if not building something huge. If this machines purpose was not meant for that, i would have shimmed the first unsuccessful pour and finish with that stage.

So if you mean all day doing precision aluminum milling is one thing, other thing is if you do all day wood.

Even so, the bigger the machine the difficulty to achieve precision multiplies. It not only the epoxy, it how many times you check all and if you take your time to repair all that you have found.

Its difficult to explain but at the end the precision of the machine depends how precise are you or how precise you want it to be. All else is means and ability to achieve it.

[Jonathan]

Per Jonathan's data, the suggestion must be that even with careful construction and preparation, the process retains a relatively high error rate, when compared to the required outcome. My addition is to suggest that the impact of the error rate, regardless of cause, could be halved by taking a two pour approach. I think that's relatively sound logic. But that not good enough.

At risk of repeating myself, the error I got with the epoxy was exceedingly small (according to my surface plate) - the large deviation you see at the end of the graph was caused by the bearing seal/lower surface rubbing on the aluminium epoxy boundary. That error went once the rubbing problem was alleviated. The other graphs with large errors were false readings caused by accidentally measuring roll not height. I'm not mentioning values here lest they taken out of context - see the original post (http://www.mycncuk.com/forums/router-build-logs/6484-sufficiently-strong-machine.html) for a proper explanation.

I heated the resin in a water bath before pouring. It clearly lowered the viscosity, but I can't comment on what effect this had overall as I have nothing to compare with.

[Rich]

Thank you Jonathan. What a mistake. I couldn't understand why everyone was so relaxed.

[Procato]

Apologies if degassing has already been mentioned.
Although I haven't got to the epoxy levelling stage on my build yet, I have had a bit of experience of some resins and silicones used for mouldmaking- After mixing and before pouring resins should be degassed thoroughly. It is very surprising how much air is trapped in the liquid even after careful mixing. I don't think you can achieve the figures on the data sheets without this process. Pouring/flow and shrinkage qualities are much improved.

https://www.youtube.com/watch?v=9sN0KT-tRsY

[routercnc]

Not done it myself but the 3 processes usually mentioned to reduce bubbles are:

1. Pouring the final mixture into another pot with a sealed hole near the bottom (e.g. duct tape), then opening the hole and pouring from the lowest part of the mixture, leaving the bubbles near the surface.

2. Once poured into the moat on the frame, flashing over any remaining bubbles with a hot air gun.

3. Not stressing over the odd bubble or two which gets trapped unnoticed.

[Procato]

I agree, those methods are the usual processes but in the pursuit of more accuracy and better working methods degassing removes the micro non visible bubbles trapped within the liquid. The video above shows just how much air comes out of a small amount of carefully mixed resin. Without degassing you are basically pouring foam.
I haven't used west systems 105 epoxy and 209 hardener yet so I might be talking rubbish but I will try to video the degassing and levelling process when I get to that stage to see if it makes a difference or not.

[Boyan Silyavski]

It works without degassing but a tiny mistake like being in a hurry could mess the whole process. last time i was pouring WS epoxy i wanted to be able to degass it. And as i said somewhere earlier in the thread, passing one time with heat gun degassing is okeish but second time is asking for trouble, third time for sure will result in orange peel surface. So yes, degassing will be great.

[reefy86]

some really great guides here and has helped me feel more relaxed trying the epoxy method so thanks guys :)

just a couple of questions though...

1. how much weight can 5mm thick resin take before cracking ect.
2. if 90% of the time all ill be doing is engraving 3d designs in wood soft or hardwood such as oak and say the other 10% will be acrylic/thin aluminium, will the epoxy resin still be advisable?

cheers

ash

[Clive S]

some really great guides here and has helped me feel more relaxed trying the epoxy method so thanks guys :)

just a couple of questions though...

1. how much weight can 5mm thick resin take before cracking ect.
2. if 90% of the time all ill be doing is engraving 3d designs in wood soft or hardwood such as oak and say the other 10% will be acrylic/thin aluminium, will the epoxy resin still be advisable?

cheers

ash

You won't have any problems with the weight of the gantry on the epoxy check out my post #56 here http://www.mycncuk.com/threads/8197-Use-of-epoxy-for-levelling/page2
.
If you are using steel it is a great way to get your rails on the same plane. ..Clive

[njhussey]

+1 ,on the above.

[reefy86]

thanks clive really helped alot :) so the best epoxy to use is the westsystem 209?

cheers

ash

[reefy86]

so in theory i should get the frame as level as a human can by hand using adjustment castors on the feet, then once thats as level as you can get it i then place the dam ontop of the frame (im using 25mm rails so my dam will be 65mm wide) then pour epoxy into the dam and let it level out then wait for about 2 weeks (to be safe) and then i can now bolt my rails ontop of the epoxy assuming its flat level?

cheers

ash

http://www.mycncuk.com/attachment.php?attachmentid=15938&stc=1http://www.mycncuk.com/attachment.php?attachmentid=15937&stc=1http://www.mycncuk.com/attachment.php?attachmentid=15936&stc=1http://www.mycncuk.com/attachment.php?attachmentid=15934&stc=1http://www.mycncuk.com/attachment.php?attachmentid=15935&stc=1

[Clive S]

I doesn't really matter if the machine is not level on the floor as the epoxy will level out like pouring water into a channel it will find it's own level. What is important is that you do not have any leeks in the moat I put a very thin bead of silicone all around the inside.
You will need it about 5mm thick. If you use MDF for the moat after the silicone you could put some Vaseline on the insides of the moat to stop the epoxy from sticking.

[reefy86]

thanks clive, do you mean the silicone has to be 5mm thick or the epoxy? i was going to use about 5mm anyways for the epoxy if so.

cheers

ash

[Clive S]

thanks clive, do you mean the silicone has to be 5mm thick or the epoxy? i was going to use about 5mm anyways for the epoxy if so.

cheers

ashThe silicone is only to stop any leeks so a very fine bead between the MDF and box section. Iff you have any leeks the job will fail:devilish:

[Jonathan]

I doesn't really matter if the machine is not level on the floor as the epoxy will level out like pouring water into a channel it will find it's own level.

Just make sure that if you're floor isn't level, it stays that way as if you move the machine the frame will distort slightly and in turn distort the epoxy slightly. That's why it's best to pour the epoxy with (ideally) all the machine mounting points (feet?) at the same height, so if you move the machine you can set them to the same height and be fairly confident of little movement in the frame.

[reefy86]

jonathon you have confused me there lol :) if the floor aint level it means adjusting the feet so all 6 feet could all be at different heights depending on how bad the floor is. so when you say if the floor aint level it stays that way do you mean to have the machine to just be as level as the floor and leave the epoxy to do its job or did you mean what my badly made drawing shows lol.

sorry if im being a little dumb here.

cheers

ash

http://www.mycncuk.com/attachment.php?attachmentid=15939&stc=1

[Blackrat]

id recommend caulk instead of silicone ... much easier to clean off

i tack welded 3mm flat bar for the epoxy bath , was super fast and simple to do with a tig welder

[Jonathan]

Your diagram is how I meant. You ideally want to make sure the frame sits such that there is no stress on it - e.g. in your drawing there are 6 feet and imagine the middle four were unscrewed so the frame isn't supported. The frame would then sag in the middle. If you poured the epoxy in this state, you would still get a nice flat surface, but if you change how the frame is mounted (e.g. adjust the feet, move it, add more feet etc), the frame will distort slightly and cause the epoxy to no longer be flat.
We're not talking much here - clearly the frame is quite rigid so wont flex much, but it's still something fairly easy to take account of which may help.

[reefy86]

ok thanks jonathan, so basically before using epoxy make sure the machine is in its final place and all 6 legs are leveled and in there permanent position?

cheers

ash

[Clive S]

ok thanks jonathan, so basically before using epoxy make sure the machine is in its final place and all 6 legs are leveled and in there permanent position?

cheers

ashAt last:applouse:

[reefy86]

clive i got an e in english 13 years ago i need to read a hundred times to your once lol :P

[Jonathan]

clive i got an e in english 13 years ago i need to read a hundred times to your once lol :P

Not much worse than my C, 7 years ago!
Just spotted you're also in Nottingham - next time quicker to explain in person perhaps...

[reefy86]

yes mate bulwell end :)

[Jonathan]

yes mate bulwell end :)

Hmm, on second thoughts...

http://www.mycncuk.com/attachment.php?attachmentid=15940&stc=1

[reefy86]

hahahahaha its not that bad :)

[reefy86]

how much lean way do you have when drilling the rails? is it easy enough with just a hand held drill or does it need to be precised? all i have in my tool cabinet is a screw driver hammer and drill lol. im willing to buy tools as i go along with the machine so not too much of an issue if i do need some sort of new tool lol.

cheers

ash

[Clive S]

how much lean way do you have when drilling the rails? is it easy enough with just a hand held drill or does it need to be precised? all i have in my tool cabinet is a screw driver hammer and drill lol. im willing to buy tools as i go along with the machine so not too much of an issue if i do need some sort of new tool lol.

cheers

ashWell as long as you have the hammer you will be fine. Oh and don't let Jonathan fool you he's going for a Phd :applouse:

[Neale]

A hammer helps, but...

The epoxy drills easily, no problems there. However, assuming M5 cap screws through nominal 6mm holes in the rails, you have a bit of wiggle room if you get the holes accurately placed. One way to do this is to clamp the rail in place as accurately as possible, then "spot" through the holes with, say, a 5.9mm drill just enough to leave a small mark in the epoxy surface. Then swap to the tapping size drill and pick up the mark to centre the drill in the hole. This is an old toolmakers' trick. However, it's quite difficult to hold the drill vertical when doing this, and if the tapping hole is slightly off then you end up with the cap head slightly off as well once fitted, which makes tweaking rail position more limited. You can do it with care, but I chose to turn up a steel guide bush with a spigot to fit the counter-bore in the rail and a central hole to guide the tapping size drill. One hand to hold the guide in place and the other to do the drilling worked OK for me. Saves a lot of drill-swapping as well. I used a similar guide bush for the tap. It's worth getting a couple (you'll need a spare, just in case) of spiral-point taps which will go straight through without the wind in/back off motion you need with hand taps. Stick one in a cordless drill on slow speed, use a touch of tapping compound, and the tapping is easier than the drilling.

[njhussey]

As Neale says a steel guide bush is a useful tool if using profiled linear rail similar to this one I made...

15945

I've shown how I did it (I used my pillar drill clamped to the machine bed) here...http://www.mycncuk.com/threads/2148-Comments-sought-on-new-build-A-CNC-Router-for-RC-Gliders-and-Planes/page40 and there's a video on the next page of my build....

[Neale]

Using a pillar drill would make an enormous difference - it's difficult to get the downward pressure using a handheld drill, then you wobble (did I mention the need for a few spare drill bits?).

Knurling the bush is just showing off. I just threw an odd bit of steel in the lathe. Should have done it before I had already drilled one and a half of the long X rails...

[njhussey]

Using a pillar drill would make an enormous difference - it's difficult to get the downward pressure using a handheld drill, then you wobble (did I mention the need for a few spare drill bits?).

Knurling the bush is just showing off. I just threw an odd bit of steel in the lathe. Should have done it before I had already drilled one and a half of the long X rails...
I knurled it because I did that one for someone on here, I even chemically blacked it for good measure [emoji6]

[Neale]

I did consider making a single bush with a hole for the tapping size drill at one end and a hole for the tap at the other end...

[njhussey]

I did consider making a single bush with a hole for the tapping size drill at one end and a hole for the tap at the other end...
But then there's not as much of the bush in contact so the chance of wobble is greater?

[reefy86]

cheers guys, im going to look for a decent pillar drill as i want this project to be perfect :) any decent ones to recommend ?

cheers

ash

[AndyUK]

Hi All,

Sorry to resurrect a four year old thread, but I'm trying to do a post-mortem of why my epoxy pour went so wrong.

I was using West 105 with the 209 extra slow, mixing 3.5 parts by weight 105 to 1 part 209 - in my book thats 350g to 100g.

The air temperature was about 21 degrees when I poured, which the manufacturer states: Pot life at 72°F (22°C): 40 to 50 minutes - we didn't get anything like that. The full description of what happened is in my build thread (here (http://www.mycncuk.com/threads/11552-AndyUK-s-Build-1-2x1-0m-Gantry?goto=newpost)), but short story is we mixed 1.3L into one pot in 6 stages, stirring for a minute at each stage.

We then thought lets leave it for 10mins for the bubbles to rise, but we didn't realise the temperature of the mixture was rapidly increasing. By 8 mins into the wait, the whole thing was burning hot and we started to pour as the plastic container was melting. That kinda ties in with the manufacturers Pot life at 95°F (35°C): 15 to 20 minutes.

How do I get it to wait 72hours? Mine was rock hard within minutes, you guys are still leaving fingerprints after days! Was it just those few minutes waiting that screwed me, or should I mix a small amount, pour, then mix more and pour over?

[routercnc]

I've only done this a few times (3 in fact, 1st time was not so good, 2nd and 3rd went OK !) and used exactly that epoxy mix. I think what has happened in your case is if a lot of mixture is altogether in one pot then the heat from the parts of the mix in the middle cannot escape so it heats up. This promotes rapid onset of the curing of the rest of the mixture which releases more heat in a runaway reaction. I'm sure they mention somewhere not to mix large quantities in compact containers.

I think you will get ~72 hours when it is all spread out in your moats, so in my view it needs to be mixed and poured straight away. I didn't see much escaping of bubbles after the stirring when I did it as it is such as dense mix, so I don't think waiting helps (is my limited experience).

I only mixed about half that amount in a relatively wide plastic jug, alternating between 105 and 209 and think I only stirred at the end, slowly to avoid incorporating more bubbles. Then I did what others had suggested (Clive?) - the "2 jugs" method.

The fresh mixed is carefully poured into a second jug, which seems to promote some of the bubbles to be released, possibly because in the thin stream that pours from one jug to the other they are forced to the surface.
This second jug has a ~5mm hole towards the bottom of one side covered with tape and once all the mix has been transferred across you hold the jug over the machine, release the tape, and this will pour out into the moat. Again this seems to prevent too many bubbles getting into the moat.

Leave a small amount in the jug as this will be very aerated.

Here was my second attempt on the X axis:
https://www.youtube.com/watch?v=FDrcpnVUcEE

And using this method on the Y axis:
https://www.youtube.com/watch?v=aw0pM_uV1kw

[JAZZCNC]

Know this bit old now but seen as I've probably got the most experience with using this method with more than 20 machines poured ranging from small to 10x5 feel should add my bit.!
Reason you failed was purely because poured to large qty then waited too long. The resin and hardener type wouldn't made any difference, would happened with any type in this instance because of the waiting. I've mixed n poured 1.5ltr without any issues but you cannot hang about after mixing. When spread across the machine the exothermic reaction is much slower so doesn't happen.

To be honest you only need to wait a minute or two then pour, any bubbles you can get as they occur by flashing with blow torch.

Also the hardner type isnt a big deal. The extra slow hardener is good on large machines because gives plenty of time to find it's level n settle. However standard slow hardener works perfectly fine even on 10x5 machine provided the conditions are good.

However in all cases it's good idea not to touch the resin or remove the moats etc for at least a week, personally i leave mine 2 weeks before touching.

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