Quite an Unusual one

[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.

[jimbo_cnc]

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.

[EddyCurrent]

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.

[cncJim]

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?



Jim

[jimbo_cnc]

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.

[jimbo_cnc]

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.