Syliavski i thought that a solvent free epoxy is a must at this procedure. Why you choose to buy an epoxy that contains solvent ( or i missaunderstood something?)Quote:
Originally Posted by silyavski
Vagelis
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Syliavski i thought that a solvent free epoxy is a must at this procedure. Why you choose to buy an epoxy that contains solvent ( or i missaunderstood something?)Quote:
Originally Posted by silyavski
Vagelis
I thought to do it , only had graphite at home. But truth is i want it perfect, so bought the West system epoxy at the end.Quote:
Originally Posted by Blackrat
I chose to buy epoxy sin solvents but they sold me one with solvents :-)Quote:
Originally Posted by ba99297
You mean the solvent was in the epoxy before you make the mix?
Good for you that they admit their mistake and you finally get your money back.
Hi,
The build is going on but i am stuck with epoxy problems. Mean BIG problems :beaten:.
Second time casting epoxy on the long sides and same problem. The area near the connecting bridges is sunk checked against straight edge. about 250mm wide visible inclination, not measured cause still not perfectly hardened but say 0.1-0.3mm . Each pour cost me 100euro :topsy_turvy: 2.5kg of WS epoxy mix.
Now for a woodworking machine this will not matter, but spending so much money on it i would like to be as Perfect as possible. Hell, at least 0.05 precision or better, real life, not exaggerated. I was striving to something like the first machine i made 0.01mm, knowing that on such a big scale it would be difficult but worth to try.
So to achieve this i depended too much on the epoxy.
Whats the f---g problem then? Everything is perfectly prepared. 21C in the garage, 45mm wide dams, 10min careful epoxy mix, all by the letter. First time i thought the dam was flimsy and contracted at certain points. Not so the second time, everything is reinforced with steel/the bridges/ and hot glue / the 10x10mm dams.
I gave it a lot of thoughts and the conclusion is : the 1600mm long bridges are the culprit. The epoxy contracts , so the bridge epoxy contracts and takes away epoxy from the rails at the exact moment when its solidifying. cause i looked 100 times after 1 hour of pour, 2, 3 hours of pour -it was ok. It happens on hour 4 to 6. Or maybe it was my mistake that the connecting bridges had to be both ends, so when all contracts , contracts equally, like a ring i mean. No money though for further experiments . I believe though that even if ring is formed the right angle between them is the culprit.
So yes, there is a problem with 3000mm rails and 1600mm distance between them. Inherent problem i mean. Not reported by any body till now but hey, did anybody who made such a big machine take care to measure it against DIN 874 straight edge? Possibly no.
I blamed the air trapped, blamed the supports, blamed this and that, but on a smaller scale i did not have any problem before, +fixed all possible doubts. So yes its inherent, until somebody prove me wrong.
I see only 2 possibilities from here on.
1. Will wait to dry for 3-4 days and mount the rails using the straight edge/ 1m/ and shim. Then will have to buy the 2000mm straight edge to continue with the build and check the rails against each other. But if there is a twist , 2000mm straight edge will not be enough or at least would be very difficult to straighten things up. To the precision i would like, i mean.
2. I knew it when pouring second time, but was not sure.:tan: . So may be third pour from scratch or half pour over this one. And on minute 45 / 21C/ cut the bridges simultaneously by some previously prepared method. Say a sliding plate or similar. The way in actual water channels the water flow is cut. Cause at this moment everything is perfectly leveled .
http://www.mycncuk.com/attachment.ph...id=13608&stc=1
Would you mind stating which WS system you used. ie the hardener ..Clive
I said here that my cross channels were 10mm wide but they should have been wider, I think that's part of the problem, maybe the channels should all be the same width.
http://www.mycncuk.com/threads/6565-...4474#post54474
WS 105+209 of course.Quote:
Originally Posted by Clive S
Mine are 30mm wide. On the small machine they were 10mm and it worked. Maybe at such lengths should have been 45mm also, same as the rails channels.Quote:
Originally Posted by EddyCurrent
If i had 3000mm straight edge i would have told you exactly what happened. Checking with the 1000mm one says the area near the cross channels is down.
Just measured it at the deepest spot 0.15mm difference.
I am starting to doubt if i should have semi filled the epoxy with something. It would have helped. And yes, WS 105+209 shrinks like crazy on 3000mm length. Visibly. You know that last time i fixed 5mm magnets to check levels. So it covered the magnets and when dried, one magnet was half out, so on 5mm thick/high all went down 0.5mm at least which is more than 10% if you know what i mean. The good thing is that it shrank equally wide wise. Not like the cheaper epoxy. But still 5kg pack
200euro...
PS. and no, it did not went down in between cause it was done so that it couldn't do it, so that's not the problem
Never done anything like that, but I'd have thought you'd want to:
1. As you say, cut the bridges. You'd do this as soon as any levelling flow has stopped.
2. How about cutting the 3000mm length into sections as well?
Someone should design a machine to level rails. Maybe screw a strip of aluminium to the rail top, and then have a travelling surface cutter that takes it's height from a laser (a rotating disco laser so both rails are surfaced to the same laser defined plane)
Silvaski, sorry to hear you've hit this snag, particularly after your success on the first machine. In an ideal world Jimbo is right, playing with epoxy is a necessary evil, which is better suited to machining. I'm beginning to wander whether I should weld the top half of my frame with rail beams and investigate whether there are machining services around to do the levelling. Knowing my luck I will have wasted several export batches which could go towards machining cost! I'm sure, the cost and availability of this alternative would likely dissuade me from this. The problem is you need a machine to level it, and the irony is that once finished, the machine you have built may be able to perform the task at hand!
Certainly your post and experience make me Dolby cautious when I get to this stage.
Daming the bridges after a time might be a good idea but you can't section the 3m sections otherwise it won't be level along the length.Quote:
Originally Posted by jimbo_cnc
Eddy's right has to be done in one pour, how about forget the bridge mix equal quantities of epoxy and pour both channels, when set find the highest rail and shim the lowest to match ?
Just a thought
Mike
Don't go to hard an your self Boyan. I find your dam idea to be a great one. The only drawback is that you lose the connection between the two sides hence they become two separate world's. I will definitely use this dam technic and will try to use something as thin as a raiser blade. Maybe cut open some beer cans and make some stripes of it. I think a thicker dam material could introduce a small unwanted wave. And as you seem to be nuts with precision you won't want that. :)
Sorry for your second fail but thanks for sharing as it is informative. Now I know it requires 21 degrees Celsius and in my case I see a problem there. In fact it even gives me some confidence as the result you have achieved is better than what I aim for in my build do to the nature of application.
Good luck with your next pour tho, if you go for one.
As jazz has said before they don't necessarily have to be the same height but they do have to be level and in the same plane. Provided this criteria is met, when you skim the bed, this puts things right, and obviously the spindle must also be at right angles to the bed.
Is there anything to be learnt from casting techniques? Arrange a large sacrificial reservoir close to the rails by widening the bridge locally but which can be cut away afterwards? However, I suspect that the shrinkage happens as the epoxy starts to gel, by which time it is not going to flow anyway. And what's happened to the "negligible shrinkage" property that we're told epoxy has?
I have a vested interest in this as I shall be putting epoxy on my own rails shortly...
Remember these videos cncJim posted ? they talk about priming the job first with a mini pour.
http://www.mycncuk.com/threads/7190-...ht=epoxy+video
It will work, but at a later point the gantry have to be squared. It will make things extremely difficult then.Quote:
Originally Posted by mekanik
I am starting to think of something like that:
http://www.mycncuk.com/attachment.ph...id=13611&stc=1 or http://www.mycncuk.com/attachment.ph...id=13612&stc=1
One problem of cutting the bridge is that if i shut them off, that has to be complete, to avoid pulling. And at the same time any spill will kill the purpose.
There must be a way to do it properly, unluckily i dont know well the material/epoxy/. Sb who works all day with epoxy will know how. cause the key may be simply to make the bridge same, wider or even more thinner to avoid the pull. But which of them. When casting aluminum i know that the hole has to be as wide as possible, cause when all shrinks, the casting holes is like a reservoir , so it pull aluminum from its core and balances the thing.
Or may be even like this, so the rails will be thinner than the bridge and situated so that they will pull from it and play its role:
http://www.mycncuk.com/attachment.ph...id=13613&stc=1
Now the question is if i decide to shim the 0.15mm, what to use, so that when the 150kg gantry goes over that it does not change. Mix epoxy when mounting and paint the bottom, then wait to dry a bit and tighten a bit when its elastic, so it stays put in that shape.
Trying to balance the flow with the shrinkage while it hardens sounds like a recipe for disaster.
Pour, flow, cut off, harden!
Cutting the rail into equal size/shape sections should give consistent shrinkage. If you do repeated bi-sections to cut the rail (eg into 4 or 8) then (with skill/slow cut) even the slight increase in pool height should be even in each pool.
edit:
More likely to work and easier: One big ring of equal cross section is the best answer. Ideally you would not have a 90deg corner near what will be the final end of the epoxy rail, a radius would be nice.
http://www.mycncuk.com/attachment.ph...id=13618&stc=1
Would this type of arrangement work, placed at the ends of the bridges where they meet the rail channels ?
http://ocw.mit.edu/ans7870/2/2.25/as...5-3/index.html
I'm thinking that when the epoxy is thin it will find the same height each side but as it hardens it will be more difficult for it to flow back into the bridge.
Hi silyavski,
Sorry to hear about your problems.
What about adding some nails/pins to the bridge before the pore? Could this maybe help the situation?
Attachment 13615
Jim
Not enough bridges IMO. I've only ever done one machine near that size with epoxy and I had 5 bridges with 2 people pouring epoxy.
To late know for you but for others like tinkerman this is why I don't like epoxy for large machines and use the adjustable top rail beam then shim as needed.
Another thought:
Are the bridge deeper than the side pools? If they are the same depth then the shrinkage should not cause flow, but if the bridge pools are deeper, then they will get inflow like you experienced because they will slump more.
Narrow deep bridges will suck less from the rails than wide deep bridges. So narrower would seem a good choice.
And all this assumes vertical walls.
I don't think painting the bottoms would do the job if you try to fix it. But how about leaving the channel sides in place or put some new ones on and after you mount the rails you pour a bit more to fill the gaps. And probably paint them as well just to make sure it gets in there.
How thin can you pour an epoxy rail? I've not used the stuff or seen a video. I 'm wondering if due to the above argument they should be done in 2 stages.
Hi Boyan
Don't understand this
It will work, but at a later point the gantry have to be squared. It will make things extremely difficult then.
I would have thought that the X rails would be level in both planes and secured to main frame before you started Gantry installation alignment ?
Mike
That could be the proper way, though not understanding the process entirely, i prefer to make it like variant 3 of mine, so the rails finish in a wider bridges. It seems the thinner the bridge the faster it cures even if logic says otherwise, cause all say more epoxy at one place cures faster.Quote:
Originally Posted by jimbo_cnc
I was having in mind something like this. As i said my worry here is that i must shut off totally the flow and remove the bridge at the moment, so any leak here will be a disaster. cause what if i shut the bridges off and leave them in place. If they harden earlier, they will pull the shut off plate toward them. So the story repeats or the plate have to be very thick. I will think again about that.Quote:
Originally Posted by EddyCurrent
Quote:
Originally Posted by cncJim
I think of adding gates and provisionally tack soldering steel profile for the bridge this time.
Before a week i was going to argue with you but now not :hysterical:. Until figure the proper way to do it.Quote:
Originally Posted by JAZZCNC
5 bridges...that's a lot of epoxy. I would do it in a blink if i though the problem is there. And that the result would be as desired. The problem seems the length of the bridge. Say a good epoxy shrinks 0.1% on length. 0.1% from 1700mm =1.7mm so if you take 1.7mm from area of 200mm long this is exactly the missing 0.15mm epoxy
Do you remember depth and width of channels and bridges, especially length of the bridges and if all checked well against straight edge?
Vertical walls. Same depth, i was very cautious after the first attempt. I agree that narrow bridges will suck less. I am almost sold on my variant 3 from the previous post, where the rails will suck from the bridges.Quote:
Originally Posted by jimbo_cnc
Considering all this, the very small gap and the time and effort, i just broke everything so will prepare for another pourQuote:
Originally Posted by HipoPapi
You could pour according to me 3mm minimum. So yes, could be done 2 times, risking other stuff like not good enough spread and leveling due to specific gravity. further complicating things with the wait times. imagine if they each shrink in different way, due to temperature or humidity difference that day.Quote:
Originally Posted by jimbo_cnc
Quote:
Originally Posted by mekanik
Both rails must be plain in the same plane. If they are equal in all other but one is higher than the other, no problem, that difference could be fixed with the gantry rails, but then you will have only one rail as a starting point for squareness . So yes, its much better all to be flat. So you have to deal with left right and squareness between the 2 rails when mounting. Cause there are 6 directions to move and fix, so avoiding 2 of them , makes things simpler.
And yes, i insist in this level to be as perfect as possible, cause in the future the plan is to surface other smaller machines inside, gantries and so. By fixing alu plates and then surfacing them. That will save each build 200 or more $$, so yes , its important. Not to speak for a long aluminum mold or so the $$$ i will make or miss, so i broke the epoxy and will do it again. Its pain in the a** but irrelevant to the money i have spent till now.
damn! was sure I'd sussed it. Very confusing.Quote:
Originally Posted by silyavski
Why do they say large areas cure faster? does it generate it's own heat for curing?
If there was room for another 3mm pour on top of the old one, I would be tempted to do that.
Out of interest, what is the deepst and shallowest depth in the 2 rails on the previous pour?
Interesting you mention fixing aluminium plate to gantries and surfacing them. I had that thought today, someone should be selling ready made flat side gantries.
Theoretically more volume epoxy cures faster, cause the heat can not escape so fast, heating the mixture so then all cures faster.Quote:
Originally Posted by jimbo_cnc
WS 105-209 gives 1h gel time, though i found that 1h 1/2 is still ok, up to 2h when is okeyish almost but still not unusable. That at 22C .
As i carefully welded the frame and a couple of times leveled the structure, the depth is 4-6mm . If i do it next time all will be steel, dam 10x10mm welded , channel >45mm wide/cause will hit the bearing blocks other wise. perfect will be 8x8mm bar. Clean, fast, beautifull. No finishing needed and most of all on such a big table water can be applied earlier so level it perfectly. Before pouring i mean.
They sell mounting straight edges but 3m one willbe 3000euro. Of course then epoxy can be applied below and then the straight edge mold it pushing it down. Then remove and do it at the other side.
So i took out the epoxy. Will have to do it again it seems. I almost have it clear. Will update here, so you tell me what you think, meanwhile will search for somebody around who builds boats or something and knows about epoxies first hand, to see if help can be obtained.
What i came till now is very simple. Extend both rails both sides 30cm each, then bridge them. When dry cut the extra 30cm each side and hope for the best in the center :-). Have to contemplate it further but i feel that this will work. And apart from this i will know for sure if i can build one day 5x10 foot CNC :-) with epoxy. Or not.
Maybe a bit off the wall but have you thought of using plastic tubes between the two sides rather than bridges - these could be shut off with clamps once the epoxy has levelled. it would be an easy job to 3d print the necessary bits.
Is there an accelerant for epoxy same as that for super glue ? maybe that could be used to make the bridge epoxy go off quicker ?
Syliavski I am sure you will find the solution. Your mind is sharp so I don’t worry. The only think I want to say is that some times we stack and we become maniac with some specs off the machines that we build. I would be the last one to talk here as I haven’t finished a machine yet. That doesn’t mean that I don’t have an opinion. So I think that the solution to your problem is more than obvious. It is #1 that you suggest. Go on with shimming. As I have read here in the forum many people use only shims. Why it would be such a big problem for you to use shims only in a small area ( near the bridges). Also have in mind that all these people who have already use the epoxy method, may never compare the straightness of the epoxy against a straight edge. The first introduction of that method that I saw here in the forum was Jonathans machine. But this machine ( as your first one ) was smaller. The scale is very important. Even a 3000mm straight edge may have (0,01%=0,3mm loss at accuracy ) I don’t want to introduce my self as the clever who knows everything. Most of the people here in the forum wouldn’t imagine the problem that you come up against. The only positive is that you give us a good lesson unfortunately by spending 200 euros. This is life. This is they way we learn, by making mistakes. No one could blame you. I think go on with shims is the best way to continue. For sure there is a solution about the epoxy method at this scale but if you want to find it you must pay. The most common characteristics that the DIYselfers have I think are stubbornness and persistence. We think that we can solve any technical issue and that make us some time loose time and money. It is useful some time to make a step back, see the things more clear and then go on again. I am no talking as an expert or as an experience constructor, I am talking as a friend ( even if I have never see you, you have helped me and that gives me the right to consider you friend ). Keep going
Just wondering if this might be worth experimenting with.
http://www.ebay.co.uk/itm/SP300-EPOS...item43cfc05850
It's almost like water so could contain a lot of solvent,but might be worth a try, i use it for sealing wood patterns and it takes about a day for any remnants in the mixing container to set solid, how does it compare price wise with the West Epoxy.
@ba99297, very nice post :applause: I think we do know most of the answers it's just we don't have access to the right (hugely expensive and massive) machinery. For example if the frame could be put under a huge surface grinder the job would be done without epoxy and super accurate.
It also makes me wonder what happens when the frame is stood on an uneven floor, okay it's very rigid and the adjustable feet would be set as accurate as possible but would the frame move over time ? and by how much ? 0.1 mm ?
Eddy this is what I have been considering. Cost again could be an issue. A naive question, but I presume the starting point for accuracy is clamping the two top rail beams upside down to an accurate level reference point (precision benchtop) and welding top down (upside down)? I'd imagine working the other way will cause significant misalignment. Is this what everyone has done? I understand it will not get to micron accuracy, but it would aid initial accuracy before contemplating need for machining / epoxy?
I've said it a 1000 times.!!! . . . Build in adjustabilty and between this, shimming and patience you will get the accuracy you require.!!
Most don't even know the accuracy they require and most are aiming far beyond there capabiltys to achive what they think the need.! When the reality is they don't need anywhere near the kind of accuracy they think they do.!! . . . . . For instance whats the point building a machine to 0.01mm accuracy for cutting woods that only need 0.1mm accuracy at best.?
Boyan if all you have is 0.15mm error over 3m length then I'd say your got it about as good as it gets with a single action. Now it's time to either shim or fill the low spot and scrape level. The important bit is that you know the 2 rails are on the same plane any surface discrepencys can be filled or shimmed out.
Look for epoxy putty and fill the low spot then scrape or sand it level checking with your straight edge.
IMO your expecting too much from epoxy over this length.!!
Some sensible comments here, bringing us back to reality. Repair the dip, fill, shim, whatever.
What matters is the rail flatness, not the epoxy flatness.
That's what I did with mine, I used some 5 minute epoxy to correct a small dip and leveled back using a long straight edge. Once the rails are fitted it's going nowhere.
At the time it was referred to as, "a disaster", but that was wrong, it turned out fine.
I think that Boyan has already removed the epoxy. G.
what about heat ? on a hot day the frame is going to expand more than .1mm ?
It may do, but it will stay flat :)Quote:
Originally Posted by Blackrat