Page 11 of 19 FirstFirst ... 910111213 ... LastLast
  1. #101
    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.

  2. #102
    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.
    Last edited by jimbo_cnc; 15-10-2014 at 12:13 PM.

  3. #103
    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.

  4. #104
    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.

  5. #105
    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

  6. #106
    Quote Originally Posted by jimbo_cnc View Post
    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.



    Quote Originally Posted by EddyCurrent View Post
    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.

    Quote Originally Posted by cncJim View Post
    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.

    Quote Originally Posted by JAZZCNC View Post
    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?

    Quote Originally Posted by jimbo_cnc View Post
    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.

    Quote Originally Posted by HipoPapi View Post
    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

    Quote Originally Posted by jimbo_cnc View Post
    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.

    Quote Originally Posted by mekanik View Post
    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.
    Last edited by Boyan Silyavski; 15-10-2014 at 03:57 PM.

  7. #107
    Quote Originally Posted by silyavski View Post
    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.

  8. #108
    Quote Originally Posted by jimbo_cnc View Post
    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.

  9. #109
    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.

  10. #110
    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 ?
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

Page 11 of 19 FirstFirst ... 910111213 ... LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •