Looking for feedback on plan for CNC router out of welded steel tubing

[Kitwn]

Daniel,
Welcome to the forum. The only problem you will have with MYCNCUK is making a choice between all the different options you will find for doing almost every part of your project.

My build experience is limited but my machine is similar to yours in having the rails mounted onto the face of the gantry. This is not the generally preferred method but does make the Z axis assembly simpler and, if you use epoxy on the face as you suggest, one aspect of the alignment is removed. Don't try to use cheap epoxy, it may well be too viscous and wil cure too quickly for an accurately flat surface. I speak from experience! West System 105 resin with the very slow 209 hardener is what those in the know recommend. Cleaning up the mess I made last time and starting agin is on my To-Do list.

I used two pieces of 50 x 100 stell box welded together to give a 200mm high flat face to take the eopxy and SBR16 rails with a 1610 ballscrew. By good luck rather than good judgement the spacing required between the gantry and the backplate of the Z axis turns out to be almost exactly the same for the rails and the ballscrew which makes this construction very simple to implement.

Your Z axis design has the same problem I faced: The linear bearings on each side of the back-plate overlap meaning you cannot fix all of them in place. I decided to have two plates, each of which has bearings, brackets etc. mounted onto one side only. This also means the whole Z axis assembly becomes a single removable unit. You also get the ability to slightly rotate the plates relative to one another for alignment purposes. Obviously the two plates need to be bolted together in as many places as possible for maximum rigidity. One of the rear plates needs to extend upward to include the motor mount.

The pictures show my machine in it's current plywood mock-up but shows the idea. It actually works surprisingly well in this state!

Kit