I've already built prototype spindle carriages, and am happy with their design, so I'll build those after I have something to mount them to.
The next most important part is the Y axis carriage, which carries the Y and Z motors, as well as the two Z axis'.
Mounting metal parts to wood rigidly is not an easy task, as the wood will compress as bolts are tightened. Their may be no way to eliminate it, but we need to minimize it as much as possible.
My original plan was to epoxy some steel bar stock to the baltic birch, for mounting the linear rails to. I was quite concerned about several things. Mainly, hot to align the rails, and how to get them all in the same plane.
About 2 months ago I had an alternate idea, which hopefully works as expected.
The rails (and some other metal parts) will be mounted to hard phenolic epoxied and inserted into the plywood.
I've found that using machine screws in holes tapped in plywood have tremendous holding power. So I figured I could go one step further, and avoid using inserts to mount the rails, by tapping into thickened epoxy, which is very tough.
So, the first step for my rail mounting plate was to route some oversize holes for the rail mounting screws, and fill them with the thickened epoxy. When cured, the excess was surfaced away, along with .002" of the plywood.
I performed 7 or 8 operations (and tool changes) over the course of about 2 weeks on this part, keeping it bolted to my table the entire time. (Home switches sure are nice, thanks Roman)
Next step was to epoxy the phenolic rail mounting surfaces to the plywood.
Once cured, the phenolic was surfaced, and shoulders for rail alignment were added for the outer "master" rails.
After surfacing, mounting holes were drilled with a 1/8" bit, for tapping with a 4mm tap. I'll have about 7/8" of tapped hole into epoxy and phenolic, and I'll probably loctite them down.
Next step was to route two clearance channels for the AB nuts, using a 1/8" ballnose. Since I was removing a lot of material, and needed this to stay as flat as possible, I painted the channels while the part was still bolted down, with a few coats of silver hammered paint. then my impatience did me in. not waiting 48 hours between coats caused some crackle in the paint, so I eventually scraped it all out down to bare wood, and started over. The scaping gouged the perfect finish that came off the router, but I'll live with it.
(Most of the machine will be painted with silver hammered paint, mainly due to the forgiving nature of it. I really wanted to put a nice smooth finish on everything, but decided against it due to the time it would take. I tend to be a bit of a perfectionist where finishing is concerned, so going hammered will save hours of filling and sanding. Remember, it is wood)
Once the paint was dry, I used a 90° bit to chamfer the edges of the phenolic. Last step was to route the profile, including a rabit at the top for alignment. All 4 sides of the Y axis "box" have rabits to key into the top plate, assuring squareness.
Now that the part is cut, it needs a few more operations to create the joint that locks the side panels into it.