[thunderdork]

I've read through and searched the forums. A lot of the threads dedicated to epoxy and granite are miles long. My question is simple, hopefully...

What is an adequate source for inexpensive self leveling epoxy?

I'd like to keep it in the context that it can be used in large format CNC mills (8'x4' or larger, steel frame). 3/4 to 1 gallon is what I have figured for my 2" wide railways at 1/4" thickness.

I have looked into precision epoxy after reading about it here. Its not cheap and was wondering if it was over kill. I've seen here that regular self leveling epoxy sold at home depot for counter tops has been suggested. I've also heard using self leveling epoxy for concrete flooring is an option. With these I'm not sure what the shore hardness or what kind of precision you can get. Maybe its not suitable or maybe it is at just 1/4" thick.

On advice from my council I would like to exclude suggestions of fillers or aggregates as I've been told its not wise at this thickness.

Thanks for any advice and/or links. It would be nice if we could come to a consensus and save future generations the effort

[rowbare]

Unfortunately a gallon of epoxy isn't going to be cheap no matter what. However I don't think it should take all that much, you really only need to be thick enough to level out the irregularities.

Have you seen this thread? He does a good job documenting what he did for his rails. http://www.cnczone.com/forums/cnc_wo...l_monster.html

bob

[ger21]

You can get 3 quarts of Epoxy for under $50 from US Composites.

[thunderdork]

Thanks rowbare,
I did read that thread. It seems he used 206 Slow Hardener and didn't like the results. Do you think the 209 hardener at 650 viscosity would work? I hear its a "tropical" hardner though... whatever that means. If 650 is still too thick, what is the viscosity to shoot for?

Ger21,
I see that epoxy but can't find any specs on it other than it has a viscosity of 600 (niiiiiice). Anybody know the shore hardness, pot life, compression strength, etc?

[thunderdork]

Alright, I actually was able to get a hold of a nice lady at US Composites, so +1 there. She sent me the specs. It looks comparable to the West Systems stuff but cheaper and easier. Its mix by volume vs weight and the ratios are simpler 2:1. Pot life is like 30 minutes she said but sheet says 40-50 gel time.

I'm gonna see if Precision Epoxy will get me some specs on theirs and see how it adds up.

[ger21]

I've been using US Composites for a few years now. It's probably not as good as West System, but it's 1/3 the price.

If you mix it and leave it in a cup, it'll get hot and cure very fast, especially if the weather is warm. If it's cool, and you pour it into a shallow pan, you'll probably get much more than 30 minutes.

I think that the 3:1 faster hardener cures a little harder.
If it were me, I'd try to add a bit of filler, like West System High Density filler. Not too much, so it's still pretty thin. Then warm the surface to receive the epoxy, and it should still level nicely.

[thunderdork]

I got a response from Precision Epoxy and forgot to post it. Turns out the viscosity is 400 cps @ 77 F. That's a big bump.

Think i'll try the US Composites first and see where that gets me. If it doesn't work out I'll spring for the Precision Epoxy. I'll post my findings back here.

[Dman65]

Hello Thunder,

I was wondering what you ended up using and how it worked out.

Thanks!

[thunderdork]

I did end up using the US Composites epoxy. I used the slow hardener but just reordered with the fast harder hardener because I really didn't need as much setup time as I thought. You can see the process here:

THUNDERDORK: DIY CNC Router - Rack and Pinion X Axis - YouTube

[Eldon_Joh]

I recently used System Three Mirror Coat which costs about 120$/gallon far as i know.

It leveled out fine, I would have had better success had the steel I poured it on been to 70F or 80F rather than the 60F or less it probably was. i then preceeded to warm it up very slowly with some candles inside the frame.
The datasheet says 700cps btw.

In anycase, I have my rails mounted now, I had scraped the epoxy flat with various tools but, after a week the rails sunk into the epoxy about half a mil. I was not impressed by that because it means this epoxy may not be appropriate, if the epoxy continues to creep more then I will have to start over with something else.. I'm thinking epoxying a sheet of 1/16th thick aluminum and then scraping the aluminum flat. My rails are 20mm wide LH style I believe, the bearing blocks are preloaded unfortunately, 6mm bolts on 60mm centers. The epoxy surface finish from the sand paper and other implements of destruction causes the rail to sink .001" when bolting it down, leaving a wave in the rail of about .0005" peak to peak in the rail.
this isn't noticeable sliding the bearing block across the rail under an indicator, but it is noticeable when clamping the indicator to the bearing block and sliding the bearing back and forth, with the indicator touching another bearing block about 8 inches away.

So my rails are 500mm or 20.5 inches long and mounted about 7 inches center to center, bolted through the 1/8th inch thick later of epoxy to an 8 inch by 2.375 inch C channel (which is welded to another C channel of the same size to make a rectangular box, outside dimensions 8 inches by 4.75, moment of inertia is 29 in^4 in the weak axis and 84 in the other.
My bearing blocks will be mounted about 10 inches apart to give me 9 inches of vertical travel, which given the taig z axis lead screw which is actually 10.25 inches long, works out about right.

Unfortunately, I think my Z axis frame, which is currently 10 pounds of a cold rolled steel weldment, may be stiff enough to overload the bearing blocks if there is more than .001" error.. most of which is due to the rails not being in the same plane. I don't have a surface plate.. the flattest thing i have is the 12 inch long ground cold rolled steel bar from the taig z axis.



TL;DR

system three mirror coat is probably good for .001" per foot autoleveling.
heat the substrate to at least 60F

I will have to watch how much the rail continues to sink into the epoxy under too high bolting torque (which for me is just to the point the stainless steel screws reach their yeild point)