"The pneumatic engage was what I didn't expect. Seems overly complex." - You have a simpler, more reliable way of engaging a socket with the drawbar? If so, do tell.

It's really not at all complex, and it works extremely well. It takes up FAR less room, and costs less, than a big multi-stage air cylinder. There's nothing to adjust, ever. It gives full use of TTS or R8 tools, both using the PDB, no wrenches. The whole thing is relatively low-stress, since it doesn't have to deal with pushing around over 4000# of springs, so no weaar, no hardened components (other than the off-the-shelf socket). And it never, never, EVER experiences "pull-out". Small price for the "complexity", IMHO. The only advantage the big air cylinder has is it's a bit faster - 1/2 second vs. 1-1/2 seconds.

Those two videos are ancient history. The first was the very first, and only, stepper PDB I built for my knee mill, using parts from my junk box. It was built in an afternoon, and worked perfectly until I retired the machine. It used the stock spindle brake to lock the spindle, operated by a 9/16" pneumatic cylinder, when the PDB was operating. The second is the very first prototype of the Novakon PDB, from almost two years ago. It uses a DC motor, and the spindle lock is integrated into the PDB itself. The "production" version is about as compact, and simple, as it can be, and works flawlessly. Only a 2" x 4" "footprint". It also integrates extensive safety interlocks, so it is virtually impossible for the PDB to engage when the spindle is turning, powered or not. And it provides true spindle RPM readout, and spindle power readout, through its head-mounted control panel.

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Regards,
Ray L.