Found this on the Workbee and Ox CNC Group Facebook page; XATC (extreme simple automatic tool changer) Alex.
Looks like he kept the collet and nut on the spindle though - must have very precise control of the spindle! Alex.
Seems like a weird way to do it given how cheap collets and nuts are, unless you specifically only need, say, 1/8" PCB tooling or something. If you want to go between 1/16" and 1/2" end mills it could be more of an issue. That said, his methodology is actually impressively crude. Instead of an encoder or rev counter photodiode or something that he can servo-control against, he uses low torque spindle operation and springs to allow detenting. The only things he then needs in his canned cycle is the locations of the toolholder/pin-sockets, activation/deactivation of the servo wrench-operator, and the high-torque loosen/tighten interpolated arcs. All of which is perfectly doable with a simple grbl machine running g-code canned cycles, using one of the coolant pins (or unlocking the unused pin via config.h) for the servo activation. The only issue I see is stalling the spindle out, and how that's managed. Could just be a timer, since without removing the nut it should be identical thread-progress on every cycle with a known backlash in the socket and the ER thread. Really relatively easy project to test out. I didn't watch the rest of the video, just the actual operation itself around 8:30, so I don't know if he addressed any meaningful considerations, but I do like it! You could really do it with an ER20 spindle, 1/2" straight shank collet chucks, and make it a hybrid TTS system.
I feel like most end mills will pull right out. You'd have to go around more than just 45 degrees to get a good grip.
As it stands it will only work with a spindle that can be reversed. To work with most spindles/routers undoing and tightening the collet would have to be done using a mechanism other than the spindle. I thought it was an interesting idea rather than a practical proposition. Alex.
Any inexpensive Chinese spindle can be reversed full power with an M4 command, it's part of the inherent advantage of 3-phase, not having to deal with capacitors and phase shifts and brushes! As long as you time the "pulse length" of M3 fairly accurately (I guess by trial and error?) you should get a fairly well cinched up collet prior to the tightening routine. The difference between, say, 20ftlb and 42ftlb (or whatever it is for ER16) is unlikely to be an enormous rotation. But the design of this changer is such that you could do more than one revolution of the holder carousel if necessary. It's really elegant in its brutal simplicity.
