Harmonic drive 4th axis for the X2

[scubaben]

I just finished my Hoss-style x2 CNC conversion and I was looking for a project to start working on. When I did my conversion I used the G540 driver/BOB combo and I have an extra driver that's currently going unused so I decided to look at a 4th axis.

I checked out rotary tables, but after looking I decided that I could build something as good or better for about the same money, and it would be a nice challenge. From the googling I've done, harmonic drives seem like a relatively easy way to get a nice 0-backlash 4th axis, and they're not too expensive on ebay. I found a NOS size 17 (~3 inch diameter) harmonic drive component set with an 80:1 reduction for a little less than $150. A harmonic drive gearhead would have been a lot easier to work with, but I didn't know what I was buying at the time (oops!).

The first step was to measure everything out and design a frame to hold the harmonic drive components. The design I settled on uses a 4x4x1.25 square of aluminum which will hold the drive and be mounted to an angle plate.

On one side I machined a 95mm pocket to receive a 6012-2rs bearing. I also pocketed a hole for the flexspline to pass through and drilled a bolt circle to mount it in place.


Here's a pic showing the pockets and the bolt circle (i tapped the bolts to 4mm x .7):


The next step was to flip it over and machine a recess for the mounting flange of the flexspline, like so:


Then I pressed the bearing into the pocket I made, and then pressed the circular spline into the bearing:


The flesxpline gets inserted through the back and bolted in place, and then the wave generator slips inside the flexspline and the frame is complete. Next steps will be to machine the angle plate so I can mount the frame and a stepper motor. I hope to be able to finish that part this week!


Big thanks to Hoss for his build thread, and all the pictures and plans you shared. CNC is really daunting but all the information you posted made it seem so mich simpler, thank you!!

Ben

[mcphill]

I have collected a few eBay Harmonic Drive parts to try something similar. Thanks for posting, and looking forward to seeing your progress. I have become a bit concerned about the ability for the HD to handle the torque of machining, so learning from your experience will let me know if I should bother to continue down the path...

[BanduraMaker]

Tap tap tap...this thing on?

How did this ever turn out. I'm considering a 4th axis now and am very intrigued by using a harmonic drive. I'd love to see how this one ends!

[mcphill]

I haven't done anything with mine yet. Too many projects, too little time!