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.

[jimbo_cnc]

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.

damn! was sure I'd sussed it. Very confusing.

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.

[Boyan Silyavski]

damn! was sure I'd sussed it. Very confusing.

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.

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.

[FatFreddie]

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.

[EddyCurrent]

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 ?

[ba99297]

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

[EddyCurrent]

@ba99297, very nice post 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 ?

[mekanik]

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.