New Build, PM2700 lathe with Acorn, Videos and Photos <upgraded to AC servos>

[Aurelien]

Great thanks for the information.
Is it the same ratio as you had with the nema24 stepper motor?

[suntravel]

yes, this works for the steppers also. Higher resolution, more torque and fast enough.

I prefer this reduction over direct drive.

Uwe

[Aurelien]

It's interesting, instinctively I would have done the opposite with a stepper. As these engines have their maximum torque very low in the turns. Currently I have my nema34 4.6nm from Z axis which loses steps when working in mm/rev and trying to figure it out.

[Aurelien]

Hello Uwe. At what maximum speed does your spindle spin? Do you have a link to buy the same servo as you for the spindle? Thanks a lot

[Aurelien]

Please I would really like a response from you thank you.

[suntravel]

I get my JMC servos here:

https://shop.cnc-technics.de/Servomotor ... en/?page=3

Spindle is limited to 3000rpm, because of the chuck.

Uwe

[Muzzer]

It's interesting, instinctively I would have done the opposite with a stepper. As these engines have their maximum torque very low in the turns. Currently I have my nema34 4.6nm from Z axis which loses steps when working in mm/rev and trying to figure it out.

Yes, in some cases, the torque falls off inversely with speed, so a reduction ratio may simply make the motor spin faster with proportionately lower torque. The result may be little or no net increase in torque at the ballscrew at speed. On the other hand, the stall torque will be increased, which could damage the installation if you run into the hard stops. Adding microsteps increases the resolution but the max step frequency limit at the controller may limit the resulting motor speed.

With servos, the torque characteristic is generally flat against speed. As Uwe points out, the maximum rapids need to be limited to avoid overspeeding the ballscrews, so a reduction ratio is likely to be sensible. That in turn allows for a smaller servo to achieve a given ballscrew torque.

To my mind, steppers generally make best sense when directly coupled, while servos would tend to drive through a reduction in the range 2 or 3:1

[suntravel]

https://www.omc-stepperonline.com/de/ts ... l-1-clts40

Torque with these steppers is for the useful range making chips higher with 2:1 reduction and you have a finer resolution for smoother cuts and better precision.

Uwe

[Muzzer]

Check the torque curve for that motor. https://www.omc-stepperonline.com/downl ... _Curve.pdf

The torque at 500rpm is around 1.75Nm. At 1000rpm, it's fallen to around 0.8Nm (almost exactly half the torque). So with a 2:1 reduction, you gain additional resolution but the torque at the ballscrew remains the same.

With the stated 1600 microsteps, 2:1 reduction and a 5mm pitch ballscrew, you'd get a resolution of 1.6um/step. With a max step frequency of 200kHz (limited by the driver), you'd have a theoretical max speed of 180m/min - but the torque would have gone long before that, due to the motor's characteristics. With a more realistic max speed of 1500rpm (750rpm / 0.1Nm at the ballscrew), you'd perhaps see unloaded rapid moves of under 4m/min.

Closed loop is definitely the way to go if you choose steppers but given the cost of servo motor/drives these days, I have always gone with servos, either used Yaskawa or new LiChuan.

[suntravel]

Jep with fast rapids no gain, but they work up to 5m/min with 5mm pitch ball screw, 2:1 reduction ok.

At 1500mm/min cutting 220 Ncm 1:1 and 300 Ncm with 2:1 reduction

500mm/min 270 Ncm versus 480 Ncm with reduction.

CL57T V4 drivers are limited to 500 khz, they are running on my lathe for Y and C axis with 400 khz reliable.

https://www.omc-stepperonline.com/downl ... T_V4.0.pdf

Uwe