Hi everyone, this is my first machine design as well as my first post and I really need some input my design process. After months of lurking and reading through sufficient build logs to familiarize myself with the general concepts of what it takes to put together a machine, I have decided finally to give it a go. I have already purchased ballscrews and linear slides in order to fully commit myself to the build, so I am set in my overall machine sizing (About 1' X, 2' Y, 4" Z travel).

I would like the machine to be as accurate as possible over this travel (within .001-.002" is possible). I would like to be able to cut wood, butterboard and aluminum. I would like to have the accuracy and finish quality to make silicone mold masters for robot components (small gear assemblies and assemblies and such), as well as general carving and machining stuff.

My main question at this point is about the main structural material for the frame. I am leaning toward an overhead gantry type design, so I can stiffen my axis more than would seem possible in a gantry that runs under the cutting surface. I plan on driving dual ballscews with 320oz-in motors. I have currently drawn up my concept with 2" steel tubing with .25" walls. I feel like this will be really stiff, but machining the tubing and joints will be a real pain and will greatly extend the building process. I am considering switching the design to 8020 tubing, or a bolt together steel frame instead of corner fittings.
Both designs have negligible tip deflection, but I am unsure what type of cutting forces I should be considering when thinking about material to use.

I have access to a mill, drill press and lathe at work and plan on doing most of the work there, and assembling at home.

Any help would be greatly appreciated! (below are design picture and components so far)

Also is it a crazy idea to buy a used surface place and bolt the whole thing down to that?

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