Use of epoxy for levelling

[Neale]

Still haven't finished my second round of epoxy. All the results I gave earlier were from just one rail, and were looking good. Then I looked closely at the second rail...

Main problem was leakage through a couple of places where I had plug-welded through to attach an internal extra steel strip to increase the depth for tapping. There was clearly a slight weep which seriously distorted the surface, leaving a virtual step at one point which was just too difficult to shim. So, I tried to recover by adding more epoxy. One problem with the first rail was that the dam was made with draught excluder strip. This left the epoxy strip on the narrow side, the meniscus needed to be removed to get a flat surface, and it was difficult to do that without impinging into the area carrying the profiled rail. So, I decided to pour a second coat of epoxy on both sides. That meant plugging all the bolt holes (short lengths of dowel tapered using a pencil sharpener and tapped into the holes), and I used gaffer tape to build a dam around the outside of the steel box. I put it on so that it stuck up above the box section by about 8mm. I did this on both rails, even the one that I had shimmed earlier, just so that both sides were the same. Biggest problem was that you get a meniscus around the site of each plug which was difficult to remove without damaging the surface. Unfortunately, I didn't leave the epoxy long enough to really harden so when I bolted down the first profiled rail, it dented the surface which left grooves which were difficult to shim. In the end, I stripped all the epoxy off, and have started again. This epoxy has only been on for a couple of days so not hard enough yet to want to start drilling and bolting.

However, a few lessons learnt:

- Make the epoxy wide enough for your rails that you can grind or file back the meniscus without touching the area that will carry the rails. In fact, so that you are only removing the meniscus for cosmetic reasons.
- Gaffer tape makes a good dam/mould but watch out when you use a heat gun for agitating the surface/levelling and bubble removal. This heat gun technique is great but tends to soften the tape which sags a bit.
- I shall never drill before applying epoxy. Drill afterwards - epoxy drills really easily. If you find yourself in the position of having to epoxy an already-drilled surface (or ones with holes in for whatever reason) then I suggest that you don't try putting plugs in the holes as this just gives problems later. What does work is to cover the holes with small pieces of Sellotape. Leaves a much better surface, and the epoxy does not seem to attack the Sellotape.
- Epoxy doesn't stick that well to steel, even freshly wire-brushed and acetone-wiped steel. I was able to split it off by getting a chisel underneath it. Maybe that was just the epoxy I was using, though, but I won't be using it to make structural bonds on steel without more testing.
- Really, really, wait until the epoxy is hard before doing anything with it. Then wait a bit more, especially in this cold weather.
- (and this one is probably a bit more contentious) - consider very carefully if you really need a bridge. I'm not sure if it causes problems due to shrinkage or not - I don't think it does but others believe passionately that it does - but it is a pain to set up, block leaks, etc. What does a bridge buy you anyway? It cannot improve the "horizontalness" of an individual epoxy strip (but might make it worse). What it does, theoretically, do is make both rails the same height. Can you build a gantry that is so accurate that both "feet" are exactly flat, in the same plane, etc? Commercially, of course you can, but then you would probably be able to machine the tops of the rails anyway. I know that I am going to be shimming between the feet of my gantry and the X carriages, so I am happy to take up the odd mm or two height difference in the shimming. My latest epoxy layer hasn't used a bridge, and so far the epoxy surface is looking good when I look along it at reflections of the wall. I doubt if I'll be taking up more than the odd millimetre of height difference. Why make things difficult for no benefit?

I shall report back when this latest epoxy is fully cured and I have fitted the rails so that I can measure how well I've done. Or not...

[njhussey]

Well I'll be watching with interest to see the results of all this...

[njhussey]

+1 ,on the above.

[reefy86]

thanks clive really helped alot :) so the best epoxy to use is the westsystem 209?

cheers

ash

[reefy86]

so in theory i should get the frame as level as a human can by hand using adjustment castors on the feet, then once thats as level as you can get it i then place the dam ontop of the frame (im using 25mm rails so my dam will be 65mm wide) then pour epoxy into the dam and let it level out then wait for about 2 weeks (to be safe) and then i can now bolt my rails ontop of the epoxy assuming its flat level?

cheers

ash

[Clive S]

I doesn't really matter if the machine is not level on the floor as the epoxy will level out like pouring water into a channel it will find it's own level. What is important is that you do not have any leeks in the moat I put a very thin bead of silicone all around the inside.
You will need it about 5mm thick. If you use MDF for the moat after the silicone you could put some Vaseline on the insides of the moat to stop the epoxy from sticking.

[reefy86]

thanks clive, do you mean the silicone has to be 5mm thick or the epoxy? i was going to use about 5mm anyways for the epoxy if so.

cheers

ash

[Jonathan]

I doesn't really matter if the machine is not level on the floor as the epoxy will level out like pouring water into a channel it will find it's own level.

Just make sure that if you're floor isn't level, it stays that way as if you move the machine the frame will distort slightly and in turn distort the epoxy slightly. That's why it's best to pour the epoxy with (ideally) all the machine mounting points (feet?) at the same height, so if you move the machine you can set them to the same height and be fairly confident of little movement in the frame.

[JAZZCNC]

Know this bit old now but seen as I've probably got the most experience with using this method with more than 20 machines poured ranging from small to 10x5 feel should add my bit.!
Reason you failed was purely because poured to large qty then waited too long. The resin and hardener type wouldn't made any difference, would happened with any type in this instance because of the waiting. I've mixed n poured 1.5ltr without any issues but you cannot hang about after mixing. When spread across the machine the exothermic reaction is much slower so doesn't happen.

To be honest you only need to wait a minute or two then pour, any bubbles you can get as they occur by flashing with blow torch.

Also the hardner type isnt a big deal. The extra slow hardener is good on large machines because gives plenty of time to find it's level n settle. However standard slow hardener works perfectly fine even on 10x5 machine provided the conditions are good.

However in all cases it's good idea not to touch the resin or remove the moats etc for at least a week, personally i leave mine 2 weeks before touching.

Sent from my SM-T580 using Tapatalk