Use of epoxy for levelling

[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

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. . Who knows, when its not measurable.


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.