Power Z Feed For Lathe?

[Reddinr]

I have a 16x40 lathe. The manual carriage feed wheel action is quite course so hand feeding consistently is tough. Also, like many lathes, the Z stop does not stop the power carriage feed so if I lose concentration and crash, the gear box will suffer. So, I was thinking about doing a semi-cnc conversion on this lathe. It seems like it would be easy to do so I must be overlooking something. Here are my thoughts. Disconnect the feed rod from the gearbox (but not the threading lead screw). I can actually do that with just a gear box setting. Put a servo motor on the feed rod. Put an encoder (MPG) somewhere for human input. Put in limit switches for crash and machining stop positions. Put in a means of setting feed rate electronically. When I want to feed, I would just manually operate the cross slide in the normal way, set the feed rate and engage the feed rod (or I could use MPG to feed "manually"). When I arrive at the machining stop point, the feed servo could automatically stop. I can then manually retract the cross slide, rapid feed the Z back to starting point, etc. I don't want to put the servo where the carriage wheel is because it would stick out too far. The mechanical threading capability would remain intact. What are experienced CNCer's thoughts on this? Has it been done?

 

[tmarks11]

How are you going to synch the feed rate with the spindle speed? That is a very important relationship to maintain to ensure a quality finish.

That is sort of a variation of the "electronic lead screw" modification that people talk about (although that is generally adapting the lead screw to a steppe for servo drive that is electronically linked to the spindle rotation for threading purposes).

If you google "electronic leadscrew" you will find a lot of info on the topic.

 

[Reddinr]

Tim, it looks like you're not too far away. Thanks for the heads-up on the google search words. I'll have another look around. I have a good encoder with an index pulse output I could put on the spindle. I've used a KFLOP board on another project and that worked quite well as a controller. I may use that on this project too. My main objective to start is just to have better manual feed and easier setup for power feed with the automatic stopping function. If I have success with that, I might try adding in threading later. It would take just the encoder bits, more software and a few wires I think. I really want to end up with a lathe that continues to act like a manual lathe when I want it to. Sometimes you just want to make something quick and CNC slows down the process. Then VFD for the spindle, then ...