Quite an Unusual one

[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?

[EddyCurrent]

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?

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.

[mekanik]

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

[EddyCurrent]

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.

[Boyan Silyavski]

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

It will work, but at a later point the gantry have to be squared. It will make things extremely difficult then.





I am starting to think of something like that:

or



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:






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.

[Neale]

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...

[EddyCurrent]

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