Lathe spindle index only?

There is a whole thread on this subject on CNCzone, here is a description of my solution.
www.cnczone.com/forums/mini-lathe/63621-cnc.html#post509784
But it was a long time ago and all the images have bitrotted...

There are some pics of the machine here, but not the critical ones:
photos.app.goo.gl/nwM9Ze59j3zi5TB77

The basic idea is to have a T2.5 pulley small enough to fit under the cross-slide, and next to that a needle roller bearing running on a plain section of the ballscrew. Then the thrust control is handled much closer to the operator, in the micrometer dial housing, with a pair of angular contact bearings, where there is a lot more diameter to play with.

I think at the end making your own encoder is similar effort like mounting a small timing belt.
Unfortunately hollow shaft encoders are much more expensive than the required parts. (timing pulleys, small timing belt and cheap encoder)

Maybe I should try ordering a slotted disc from a PCB maker for 2USD? They do drilling and milling and it is a matter of sending them the correct pcb file.
 

I converted my lathe from parallel port to mesa when I added linear encoders. Prior to that, I had zero problems threading with the parallel port using this 65 tooth, 260 count disk using a quadrature software encoder on an ancient PC. I only used the spindle encoder for threading (<150RPM) so I'm not sure what the limit for this setup was. I still run 4 identical ancient PCs for my LCNC machines but they all have mesa cards now.

3d printed timing pulleys are a great low cost solution for the low load timing application.

The slotted disk (I used thin copper coated pc board I had laying around) is easy if you have a working CNC router or mill. The finicky part for me was aligning the sensors to the teeth. To get quadrature and index signals all three encoders need to be positioned just right.  

I mounted my ballscrew bearing block directly to the apron. (original mount was damaged) This gives me just enough room for a 12 or 13T timing pulley to pass under the X slide. I may have modified the bearing block for clearance. When you remove all the manual clutter, there is room to mount the x stepper directly underneath so you end up with a shortened x axis that doesn't get in your way.

I used a wireless MPG for a while but found the joypad was much better for jogging and feeding at a consistent rate and I use MDI when I need precise movements anyway. As a bonus, it's easy to cut a nice 45 degree chamfer using the analog stick! 

timo wrote:

Unfortunately hollow shaft encoders are much more expensive than the required parts

 

One option might be an engine crank encoder:

For the cross slide I oredered a 12mm ballscrew. If I can find room I will mount the ball nut under the cross slide table. If not, the screw I bought is long enough that I could mount the ballscrew on the back side of the cross slide table.

I'll be going out of town for a couple weeks, but when I get back I think I will do some examining for the encoder situation.

I saw a video of somone doing threading on linuxCNC using a missing tooth scheme. I may look into this more when I bored in my hotel room next week.

Thanks again for the comments