[jbrookes]

Hello
I want to have a stepper/servo motor turning on the tailstock (TS) synchronized with rotation of the lathe headstock (HS).
rpm - 50-100
accuracy - not precision, but shouldn't drift over time
force - nil

What I've looked at so far:
1. optical encoder on HS emits pulses to drive a stepper in TS. An intermediary mcu-driver. The cheapie optical encoders do 96 ppr, whereas the steppers need 200 ppr. But there are $50 optical encoders with 200 ppr.
See #2.
2. A stepper direct drives the HS, or turns passively on the HS. This is synchronized with a stepper on the TS via two driver boards and one set of control signals to drive both, but in opposite sense. (cw-ccw). The attraction of this over a passive optical encoder is to be able to drive the HS precisely at will...In this application, no appreciable power is needed. It would be useful, in general, to have a stepper rotating passively (no voltage in), and then cut the power to the HS main motor to enable the stepper to take over. Is this possible from a stepper perspective? The HS would be turning at up to 2000 rpm when the stepper is in "passive" mode. Though, for the application here, we are at very low rpm - 50-100.
3. a servo arrangement. Not my favorite, but I'm keeping open mind.

Any help or opinions appreciated. JB

[mike_Kilroy]

if the ts force is nil, why put synchro thing on it?

[Al_The_Man]

As Mike intimated, why not a live centre?
If there is no connection with either end in the application then presumably you would need a chuck both ends as in a double end lathe?
Al.

[doorknob]

If I have understood your option #1 correctly, wouldn't that operate with the hs and ts always being slightly out of sync?

For example, 200 steps per rev equates to 1.8 degrees per step. So wouldn't the hs rotate by up to 1.8 degrees while the ts is stationary, after which the encoder would output an index signal to step the motor on the ts by 1.8 degrees to "catch up" with the hs, but meanwhile the hs is still rotating, so the ts will always lag the hs by up to 1.8 degrees.

Maybe a variation on that scheme would use microstepping of the ts motor, with a "phase-locked loop" operating to keep the hs and the ts in sync.

[Al_The_Man]

It would help to know if this is a CNC environment or a manual M/C?
Also whether you need 1:1 or variable gearing?
IOW is the TS operating separate from the H.S.?
Al.

[jbrookes]

As Mike intimated, why not a live centre?
If there is no connection with either end in the application then presumably you would need a chuck both ends as in a double end lathe?
Al.

Thank you all for replies - my spam filter was junking the notices. At this point I have decided to drive the hs and ts by two steppers running on the same pulse train. So am setting up identical timing belts for each.