Help choosing parts: y-z luthier router

It seems workable. Don't put in more adjustment than you'll need, unless you're adding extra rigidity somewhere. And the belly of a violin is a significant compound curve, which means your base platen probably needs to be able to adjust to keep the surface tangent facing directly up into the cutter as you move around the perimeter, especially if you plan on using any undercut dovetails anywhere. That might be a complex job short of a 5-axis mill.

 

As long as they're all parallel to the top plate's main axis rather than its curvature- ie. you're staying within a half inch or so if the edge and not doing any crazy inlays or the F holes or anything- it shouldn't be a problem then.

Build the main body so that the router naturally sits roughly a medium tool-length above the edge where it would normally be positioned in the middle of its range, then just add, say, 50mm of adjustment back to front and maybe 100mm up and down to allow for different tool lengths or different edge profiles. This would allow you to use larger-diameter single-start trapezoidal screws that will give higher precision, less backdrive, better locking, and smoother movement.

You could also permanently mount some cheap digital calipers as a DRO for part-to-part consistency, as long as both axes have less than 150mm of usable travel.

 

Honestly for such a small, specific machine, I'd probably just buy a 5" cast iron drill press X-Y table for like, $60- they're all just knockoffs of the Wilton CS5, you could use that instead though the quality isn't Wilton's usual- and work out how to mount it vertically and attach the router. It has dovetail ways with gibs like an actual manual mill, making it far more rigid than anything you can reasonably make out of extrusion. Downside of course is sawdust and way oil, but lots of people machine wood on Bridgeports and don't seem to have issues with binding and rust. Not sure how you lock the axes, that might require a little research, but something along those lines is where I would be thinking initially. Whatever you go with, an axis lock will be critical.

Maybe use some C-Beam as machine framing along with some solid aluminum plate for heavy-duty connections, probably 1/4" would be good enough. You could even concrete-fill the extrusion for more rigidity and less resonance. Not that I expect cutting forces to be huge, but there's a reason the nicest machines are big and heavy. The Openbuilds parts are designed much more for CNC with stepper motors constantly engaged and lots of constant motion. I'm personally not really into wheels for anything except inexpensive 3D printers and laser cutters- linear profile rails got so cheap lately- but plenty of people use them without too much issue.

Unlike many real DRO scales without a Z channel pulse, using calipers as DROs gives you a zero, too- just crank until you lightly close the caliper jaws, zero them, and you have a repeatable reference point that you can base future projects on. They're plenty good to 0.2mm.

Up to you, but those would be the directions I'd be looking at if I were doing this project.

 

It's a drill press vice, but it has a mill-style X-Y table built into the bottom for precision positioning of workpieces for drilling. Since you need a Y-Z stage, you just flip it up and hold the router in the vice somehow.

Not really sure- people have made axis clamps, but I'm not sure off-hand whether there's an official option. Axis locking can be tricky, especially if you're not trying to destroy the surface of the metal with a screw clamp. Machines with gibs usually have some way of pressing into the gib with a screw so that it binds up the dovetail slide.

Worth a shot, before buying any specialized parts. Even if it doesn't work, it'll tell you what you need to do differently. Can always attach stuff to wood as well, like extrusion or linear rails.