Quite an Unusual one

[Boyan Silyavski]

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.

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.

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.

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.

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

I think of adding gates and provisionally tack soldering steel profile for the bridge this time.

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.

Before a week i was going to argue with you but now not . Until figure the proper way to do it.

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?

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.

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.

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.

Considering all this, the very small gap and the time and effort, i just broke everything so will prepare for another pour

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.

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.

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

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.