Originally Posted by
PaulAmelang
Hi Wayne,
I think I have less experience than you do.
The gantry and Y-beams will be fabricated out of 1/4" steel plate. The way I have it set up, the Y-beams and gantry can be cut from one 4x8 sheet. If I bought an extruded tube, I would have to buy the entire thing, probably a 20' or 24' section. Also, fabricating the gantry and y-beams from plate allows me to build them around XPS cores. My options for attaching the pieces are either edge welding or bolting steel angle to each corner, or epoxy. I believe edge welding will be acceptable for the gantry since I will connect the pieces before leveling the face. Except.. I'm pretty sure doing so would melt the foam core, so I guess that idea is out. Well, there are multiple ways to skin a cat. I believe the tolerance for 1/4" hot roll steel is about +/- 0.03". I believe Precision Epoxy says their epoxy will level to within 0.003" (I didn't get that figure from their website, I saw it second hand on a forum). I plan to level the table top and the faces of the Y beams and gantry with epoxy. Simulations seem to show that you can still achieve acceptable rigidity with a layer of epoxy.
Luckily I live in Texas in the country, and the local metal market has outstanding prices, although they only carry hot roll "barn steel", and of course the prices have gone up a lot lately on steel everywhere. If I need aluminum or any special alloy I can get it from Austin or Houston at a price better than is available online. I will compare the prices of aluminum and steel before making the purchases, because I don't think aluminum prices have shot up as much as steel, but I doubt that the disparity would make aluminum the more economical option for the bulk of my materials.
I plan to make this baby with a circular saw, homemade saw track, drill gun, some clamps, and some measuring tools like a caliper, square, 123 blocks, ruler, and indicator. I've designed it to be able to be assembled precisely this way.
About the epoxy meniscus: If the restraining lip is above the epoxy line, the meniscus will be concave. If the meniscus is below the epoxy line, the meniscus will be convex. If the lip is equal to the epoxy line, the meniscus should be minimal. My best bet is probably to make a perimeter (some thin sheet metal) that sticks up precisely 3/16 around the perimeter, and then calculate exactly how much epoxy is needed to raise the surface that amount. Of course it won't be perfect, but I bet I could get it pretty close and reduce the meniscus effect considerably this way. In order to minimize the variable of how much epoxy is left in the bucket, I would want to use a spatula to get out every drop I can. It is also standard practice to mix the resin system in a container, then transfer it into a second container to mix it again before pouring it, that way there is less of a concern of any of the resin/hardener not mixing completely.