Centroid Community CNC Support Forum

I just got in a couple of non reversible drives for my lathe. I can use it as is and only have forward. I can add in a relay to reverse polarity but this has a few small issues. Biggest problem is that when reverse spindle goes off and it releases the relay it instantly reverses the polarity to the motor. This probably won't be good for the motor or drive. I can probably edit the PLC so that when reverse spindle turns on there is a half second delay to wait for the relay to engage. Then I would need to have the relay stay on until the motor stops. I'm leaning towards just having the lathe capable of forward only.

So here is the question. Why might I need reverse spindle?

Threading to a shoulder, back-side part-off, rigid tapping off the top of my head. Some people prefer left-hand boring tools so you can see the cut without leaning over the work.

You are better off going with a 3-phase motor and a VFD. You get "instant" reverse without damaging the motor, spindle braking, and, of course, variable speeds.

Hi Murray

Any reason you can't insert an M5 followed by G4 Pn (where n = seconds delay needed) followed by M4 at the appropriate reversal points in your program ?

You need reverse for tapping, but no prob to just switch polarity, that worked on old production machines for years...

Uwe

Nigelo wrote: ↑Sat Nov 26, 2022 1:02 pm Hi Murray

Any reason you can't insert an M5 followed by G4 Pn (where n = seconds delay needed) followed by M4 at the appropriate reversal points in your program ?

I have been doing a little reading in the PLC. I'm not sure yet but I think that the spindle actually starting to spin may be a different item than the reverse relay engaging. I'm hoping I can do a little editing with delays there to make things work. The problem I have is the reverse relay must be on before the motor starts spinning and off after the motor coasts to a stop so 2 different parameters.

suntravel wrote: ↑Sat Nov 26, 2022 3:44 pm You need reverse for tapping, but no prob to just switch polarity, that worked on old production machines for years...

Uwe

My current spindle setup is a 180 VDC permanent magnet motor fitted with an encoder and a 1 way drive. Polarity can only be switched with the motor stopped. Can I do rigid tapping with this or do I need a servo spindle?

tblough wrote: ↑Sat Nov 26, 2022 12:57 pm Threading to a shoulder, back-side part-off, rigid tapping off the top of my head. Some people prefer left-hand boring tools so you can see the cut without leaning over the work.

You are better off going with a 3-phase motor and a VFD. You get "instant" reverse without damaging the motor, spindle braking, and, of course, variable speeds.

Unfortunately I'm past the point where putting in a 3 phase motor with a VFD is feasible. That is what I have as a setup on my other machines though. Good point about the left hand boring tool.

Sure this works, Z-axis is following the pulses from the encoder.

You can add a time delay in M3/4 macros, or code to make sure the spindle speed is 0.

Uwe