Servo & spindle pulley question

[xbartx]

Looking for advise on my Boxford lathe, I have it retro fitted it with new electronics and have a servo ordered for motor drive. My question is about the servo and spindle pulleys. I need to obtain a new pulley for the servo anyway and my question is if I should try to go with 1:1 ratio to be able to use the encoder on the servo. If I go that route should I get a toothed pulleys? The spindle has a huge bore and would need to enlarge anything I bought. The easier option would to buy a off the self fully for the new servo and forgive the use of the encoder.

-Brad

 

[Eddyde]

IMHO, Toothed "Timing" belts are the only way to go for servo/stepper motors controlling motion. I'm not sure of the hardware, software you are using or what you are trying to achieve, but you should be able to program the ratio between different sized pulleys.

 

[JimDawson]

Is that a geared head lathe? Your pulley sizing really depends on the torque of the servo, I would pretty much match the original motor specs and pulley sizes. If you want finer resolution on the spindle position, replace the encoder. I have a 1024 PPR encoder on my lathe.

I really need a bit more information about the original configuration of your lathe.

 

[xbartx]

Is that a geared head lathe? Your pulley sizing really depends on the torque of the servo, I would pretty much match the original motor specs and pulley sizes. If you want finer resolution on the spindle position, replace the encoder. I have a 1024 PPR encoder on my lathe.

I really need a bit more information about the original configuration of your lathe.

Sorry for the delayed response ( our internet was down for several days)
The lathe I'm retrofitting is an small, older Boxford TCL 160 lathe. The original motor was a 500W 180 DC permanent magnet rated at 4000 rpm, not sure of the torque it put out. It used belts and stepped pulleys along with motor speed to run the spindle. The servo I have on order is 1000W 3000rpm 3.18Nm. My thought was to get 1:1 ratio on the servo and spindle to be able to use the servo encoder. The hardware/software I'm using for CNC is Centroid Acorn & CNC12.
-Brad

 

[den-den]

You don't need 1 - 1 ratio to use the encoder. You do need cog belts and pulleys. Size the pulleys to get the torque and spindle speeds that you need and use the software to deal with the encoder pulses / spindle turn ratio.

 

[JimDawson]

I did some research on the original motor, best I can come up with is it's about equivalent to my axis motors on my mill. And that's a small lathe. So the 1kW motor you chose should work OK for what you want to do.

Now tell me what the encoder is going to be used for. Just RPM control, tapping, indexing? You have that perfectly good encoder wheel on the back of the spindle that is 1:1 already. As @den-den says, you don't need a 1:1 ratio, the software can sort that out.

I don't have a timing belt on my lathe, just a triple band V-belt at ~1:1, the encoder I use is on the spindle. 7.5kW servo motor. In this application, a timing belt might be better, but with the encoder on the spindle you can go either way. Doesn't matter if the motor/spindle connection is not rigid.