A deep-Z 4-axis CNC router

[awerby]

This has been in the works for a while, but I'm feeling good about it now since we just got it to run, and it seems to actually work (Yes!). The inception of this machine happened with my acquisition of some slightly-used Adept/NSK automation units. These were nice units to start with because the hard part is done for me - they already contain ballscrews and linear slides, correctly mounted in a fairly structural manner, with plenty of threaded holes to attach to. There were a few problems, though. First off, they came with some rather exotic Tamagawa AC servo motors, that I had no idea how to drive. Also, the screw pitch is extremely steep, at about one inch per revolution, which means I can't count on much (if any) mechanical advantage from them (the original application was positioning, not cutting). But I decided that we could deal with both issues by replacing the servos with steppers, since the steppers are easy to drive (thanks to Geckodrives and Mach3) and they have best torque at the slowest speeds. Since the screws will provide plenty of speed, I figured that I'd be using the motors to best advantage this way, even hooked up direct-drive.

I got the rotary table on Ebay, and also an old lathe tailstock. So the basic task was to build a frame strong enough to provide a rigid structure that was capable of disassembly, while remaining orthogonal. Since most of this frame remains stationary, steel seemed like the best choice of material, with some aluminum channel providing a way to mount the timing pulleys that drive the X-axis from both sides with a single motor. Another piece of the same stuff came in handy for making a spindle mount that attaches to the Z-beam. The 18" long Z axis is rather heavy, so we decided to boost it with constant-force springs on either side to keep it from crashing down on power-off.

While I haven't cut anything with it yet, it seems pretty rigid. I was figuring it would mostly be cutting foam, but it seems like it should be able to handle wood. The spindle is another Ebay find; a Precise-Rockwell 1 hp unit capable of 45k rpm. (If anyone knows where to get collets for it, I'd love to hear from them. I could also use a speed controller for this thing.) In the future, I'm thinking of building a gizmo to tilt the spindle for 5th and 6th axis work, but I want to try it in 3 and 4-axis mode first. We still need to make some cover plates, and put together some kind of fixture to mount parts on the rotary table faceplate, but it's basically together, so I thought I'd share. They aren't great pictures, and sorry about the messy shop; I'll shoot good ones against a clean background once it's all finished...

Andrew Werby
www.computersculpture.com