Rotary encoder on rotary table

[MidniteMachinist]

I've wanted to add an encoder to my 6" import rotary table for a while now. Ideally, the encoder would be directly driven by the table itself, but there's no room inside the casting. I thought about mounting an encoder externally, and driving it with a contact wheel, but keeping chips out of it would be a pain.

I decided on driving the encoder with the hand wheel. This has the drawback of backlash. As long as you're careful to only rotate the handwheel in one direction, you're good. But, if you turn it even a little backward, you've lost the accuracy of your readout. To prevent this, I incorporated a keyed sprag bearing (BEARING). This bearing will only turn one way, and locks up in the other, so I can't mistakenly turn the handwheel backwards, and the lash will always be taken up.

For the encoder, I used a 3600ppr push-pull encoder with a 30mm hollow shaft (ENCODER). Because it's a quadrature encoder, the 3600ppr is actually 14,400ppr (3600 * 4). My rotary table has a 90:1 reduction, so that gives me 1,296,000ppr. Theoretically, this gives me single arc-second resolution (360 degrees / 1296000 pulses = 0.0002777 deg/pulse). I seriously doubt it's that accurate, and I don't have a way to test it. Either way, it'll be more than accurate enough for my basement hobby shop.

Now, pictures!

Exploded view. Left is a spare crank handle from my mini lathe. Next is the handwheel. It's internally keyed to match the rotary table shaft. The slot on the end fits the internal key in the sprag bearing. The hollow shaft of the encoder is kinda like a collet, and uses a screw to cinch down around the handwheel shaft. I cut the heads off some 3mm screws to make studs, to attach the encoder to the adapter, as it saved space vs. screws inserted from the back. Lastly, the adapter... The bearing and keys are already in, and you can see the split in the lower flange to allow it to clamp to the rotary table.


Assembled. This is why I used studs and nuts... Had I used screws to attach the encoder, the gap between the flanges would've had to be wide enough to insert them. I knew this contraption would stick out pretty far, so I did what I could to minimize that.


Back side. You can see where the handwheel shaft keys into the bearing. I had to file a groove in that key, to clear the rotary table shaft housing.


Installed on the table. It replaces the handwheel and moveable dial, and clamps to the stationary flange that has the zero mark and vernier scale on it.


Another installed shot.


Let me know if there's anything more anyone would like to see, and feedback is always welcome. I'll also be posting a video of the machining, assembly, and testing to my YouTube channel, I'll post a link here when it's up.

Cheers!