Hello, New to the forum! Hoping to get some help selecting parts for a project I've had in mind for a long time. The needs of violinmakers are particular, and while we mostly use hand tools, there are some tasks which can benefit from machining, especially since as we age they become more punishing on the hands. I have dreamed up a type of overarm pin router, though in this case the pin isn't used to guide the work along a template - instead the pin is used directly on the workpiece to maintain a consistent distance from the edge to the cutter. The point of the design is to position the cutter along the y and z axes so that the workpiece can be guided by the hands against the pin, allowing cuts of a specific depth to be made - for example, to rout an even trench of 1.2 mm wide by 2.5 mm deep at precisely 3.4 mm from the edge of a violin belly for the purfling (a decorative inlay) to be glued into. Please see attached for a very crude sketch which also lists the pieces I think I need. I am hoping some of you will be able to tell me if I am missing any parts or if I should consider choosing different ones, for example more robust parts to ensure stability. Note that I will not be using any motors to control the screws, but will be operating them by hand. Once the z and y axes are adjusted with the knobs to the appropriate setting, the machine will be "locked" into that setting and the machine will be operated in that position. Thank you all so much in advance!
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.
Thanks for this! That's helpful. Not milling the arching with this rig, just the overhang, edge thickness, and purfling channel - all "straight up and down" work.
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.
That's the plan, and thanks for this - very helpful. So with those things in mind, do the parts I've listed from the open builds store make sense? As in, do the screws and anti-backlash nuts work for what you suggested? I'd also like the whole assembly to be rigid enough and so if the thicknesses of rails need to be bulkier, or if I ought to build in some bracing, let me know. The DRO idea is a great one I hadn't considered. I currently set up my similar tools (drill press, stew-mac purfling rig, etc) with a Veritas tapering gauge in 0.2mm increments, which is acceptable tolerance for these tasks.
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.
Thank you again for the detailed, considered response. I really appreciate your time and expertise. I'm not super clear on the function of the Wilton-clone piece here, sorry to be daft. Im a traditional hand tool worker and don't have very much knowledge or experience on machine tools. Locking the axes with the open builds parts is absolutely key, and something I'm unsure of how to do. I figured it might become more obvious to me what to try when I have the machine in front of me. Perhaps I could drill and tap some holes in the gantries and use some bolts and knurled nuts to lock them to their place on the rails when set? I'm beginning to think I might have to go with my initial idea for this and make it out of wood, with the movable parts sliding on tongue and groove. Much more in my range of skills.
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.
