Finished making a rotary 4th axis for the CNC mill. It is 276oz-in stepper motor directly connected to a 11:1 planetary gear head from Harmonic Drive Systems. It's pretty accurate with minimal backlash. With a 10 microstep Gecko stepper drive, it works out to be about 61 steps per degree of rotation. There is plenty of torque for rotary carving, I can't stop the rotation by hand. The listed backlash is less than 1 arc-min and rated max torque is 133lbs-in.
The gear head was purchased from eBay over a year ago but other projects has kept me from finishing the rotary axis. Hackaday,com was featuring a Trinket MCU contest and I figured a Hackaday logo, rotary engraved into PVC plastic tube, would be my entry into the contest. This was a week before Halloween 2013 and I wanted to make some PVC engraved LED "Candles" that was to be place around the front door for Halloween Trick or Treaters. I didn't finish the rotary axis in time so I submitted my older CNC Etch and Sketch project to the contest. My entry did win a Trinket microcontroller board, thanks HACKADAY!!! I did finish the rotary axis a week after Halloween so these are some images.....
This is the type of planetary gear head I found on eBay. I used my lathe to make a aluminum flat plate and spacer to mount the 3-Jaw Chuck. It was really a simple and easy build, I just don't know why it took me so long to do it.
Short video showing rotary axis carving in PVC tubing.
Rotary axis mounted on the CNC Micromill. I used the tail stock from my mini lathe to support the end of the PVC tube. I made a MDF end piece to help center the tube to the tail stock.
Close up image just after being engraved. I used a .075" diameter end mill with a cut depth of .1", 10 ipm feed. I went slow since I didn't want to break the small end mill. PVC plastic cuts really nice and easy.
Sanded and cleaned up.
What it looks like when lit with LED flashlight. Pretty cool.
Another engraving. The Detroit Tigers almost made it to the World Series this year. I did go to playoff Game 4 against Boston. We won that game but eventually lost the series.