[Mark86]

Thanks for the input.

The plan was to weld the "frame" together, let that settle for a couple of weeks.
Next I would fill it with EG then let that settle for a couple of weeks then I would get the top of the bed ground or milled flat.

I do like the idea of upside-downing it and using the epoxy surface as the surface to mount the ways to...

Would a surface flat to a thousandth of an inch be possible by casting a layer of epoxy on top of the EG?

Cheers.

[harryn]

The surface plates are quite flat - I think yes to your question on tolerance.

The limitation to keep in mind is that self leveling epoxy is designed with wetting agents to really level out well, with no fillers. The final surface is not hard like EG or steel - just very flat.

Any internet search engine will find a lot on these.

[BobWarfield]

Note that the hardness of the E/G in this type of design is less critical, because the inserts provide most of the support for the linear rails. A lathe would be a particularly good application because nothing sits on the E/G but the rails. Hence the job of the E/G is then most to be stiff rather than flat. You could build a slant bed design pretty easily too, if you so desired.

It's worth taking some time to carefully think through how to get the headstock and spindle properly aligned with the bed rails and similarly dampened with E/G.

Cheers,

BW

[Mark86]

So...

Interested in the flipped bed idea and using an epoxy surface plate to mount the ways of this lathe to, I went out and got some epoxy and a slab of granite just to see how flat and suitable the epoxy bed would be.

Here's some pics and the result. In the photos the surface looks like glass however the epoxy hasn't cured yet... Hope it stays this flat.

The granite is just a 500mm square paver thats been cut in half.



I poured 60cc's initially to make sure the epoxy wasn't going to leak out the sides.



Then poured another 300cc's making a total of 360cc's which works out to be about 3mm's of epoxy over the surface.



Next, I ran over the surface with a gas stove lighter to get rid of all the bubbles. This worked a treat and resulted in the glass like surface shown here. Like I mentioned above the epoxy hasn't cured yet so I'm hoping the end result is as flat as this.



I'll post an update once its cured.

Now.. How do I test for flatness? guess I'll be pulling out the straight edge and feeler guages?

[BobWarfield]

Your flatness will be decent, but not awesome. However, you don't need surface plate flatness for this application. You should level your embedded mounting points, bolt down the rails, and pot them in place with the epoxy so they're partially submerged. They'll be well supported that way and flatness will not be the issue.

Cheers,

BW

[harryn]

Hi, just FYI, here is a link to a firm that sells self leveling epoxy and some info on it. It is not "just epoxy", but also includes wetting agents to help it flow out better.

http://www.precisionepoxy.com

One method to obtain an indication of level and flatness is to put some soapy (not sudsy) water on it. Soapy water has very low surface tension, and will show high / low spots very fast.

Another method is to put a sheet of glass on the surface. Float glass is quite flat (not perfect, but pretty decent) and imperfections will be visually obvious. Some people combine the water and glass methods to force a sort of image into the glass / surface plate interface. There are precision instruments made which are based on this technique.