Quite an Unusual one

[ba99297]

Hi Neale,
This is specifically a casting epoxy, its not a coating epoxy. It specifically says 0.1% shrinkage in its technical sheet, and by no means its a cheap epoxy , its simply cheaper than imported WS epoxies.
I also read a lot of documents about epoxy and all say the same- 3 types of shrinkage, and exactly this type is due to non reacting solvents. This is not shrinkage due to temperature cause it happens after the initial hardening. From the company started to argue with me, saying this is not possible, it never happened, until the moment they understood that i know a lot of sh^t about epoxy and they agreed that this was because of the cheap solvents. That was the moment they agreed to break their policy of no return, once its opened.

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?)

Vagelis

[Boyan Silyavski]

What about adding a filler like ATH ?

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.

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?)

Vagelis

I chose to buy epoxy sin solvents but they sold me one with solvents :-)

[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.

[Boyan Silyavski]

Hi,

The build is going on but i am stuck with epoxy problems. Mean BIG problems .

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 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. . 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 .

[Clive S]

Would you mind stating which WS system you used. ie the hardener ..Clive

[EddyCurrent]

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

[Boyan Silyavski]

Would you mind stating which WS system you used. ie the hardener ..Clive

WS 105+209 of course.

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

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.

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

[jimbo_cnc]

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?

[jimbo_cnc]

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)

[Tinkerer]

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.