electronic lead screw

RJSakowski said:
...The concern is that the stepper motor has a relatively flat torque x rpm curve so very little is gained by using pulleys...
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No, whatever torque the motor develops will be multiplied by the gear ratio, regardless of rpm.
 
Qtron said:
A while back Briney Eye was quoting huge forces on the saddle, 700 lb plus, for 8 tpi threads in harder steels,, He had received a torque gauge but dunno the outcome of measurements.
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Pulleys would provide torque below 300 revs on graph?
 
kb58 said:
No, whatever torque the motor develops will be multiplied by the gear ratio, regardless of rpm.
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Right, but a 2:1 increase in torque by virtie of gearing is accompanied by a halving of the motor torque by virtue if the soubling of motor speed to provide the same output rpm.
 
RJSakowski said:
I received my encoder belt on Monday; the last item on my BOM. However, I also had carpal tunnel surgery that day and had to delay the mounting of the encoder. I managed to get the encoder mounted and connected everything together for a test run. I was disappointed in the available torque. I expected more from a 600 oz.-in stepper. Running the spindle at 175 rpm and the 12 tpi lead screw at .125"/rev. (8 tpi) , the stepper was turning at 262 rpm. I could make the motor lose steps with 40 lbs. of force applied to the carriage. I tried cutting a 7/16 -14 tpi thread and was able to cut the thread although the motor encoder kicked in to make up lost steps.

One obvious improvement would be to increase the supply voltage. I am running a 36 volt supply and the drive is capable of handling 48 volts. From the torque curve, this would give me about 20 - 30% more torque. A simple experiment would be to use the 602 gear box to do a 2:1 reduction, doubling the torque. This would be similar to Clough42's 3:1 motor pulley ratio. The concern is that the stepper motor has a relatively flat torque x rpm curve so very little is gained by using pulleys.
View attachment 307253
Here is that curve for my motor, running at 36 volts, derived from the published specs.

Another possible issue is driver tuning. Supposedly, the driver has an autotune feature but this may be making compromises for torque for the sake of other features. StepperOnline is secretive about the tuning software but others have suggested that Leadshine's tuning software is the one to use. I'll have to make up the serial cable. It's been a long time since I've done any work with RS232 cables but as I recall, only RX, TX, and GND are needed and the RX and TX lines are crossed. (Someone please correct me if I'm wrong.)

I am using a setting of 1600 steps/rev on the driver and 200 steps and 8 microsteps in the Clough42 software. This gives me the correct spindle to lead screw ratio. However, other have used the motor encoder resolution of 1000 pulses in setting the driver and in the controller software. Is there possibly an impact on torque there?

As I recall, a stepper has its best torque output at full step positions. Would there be an advantage to decreasing the number of microsteps? So many questions to answer.:rolleyes:
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Full steps = Max torque, but far more prone to 'mid band resonance'. (Bench tested!).
 
Qtron said:
Full steps = Max torque, but far more prone to 'mid band resonance'. (Bench tested!).
Click to expand...
A while back Briney Eye was quoting huge forces on the saddle, 700 lb plus, for 8 tpi threads in harder steels,, He had received a torque gauge but dunno the outcome of measurements.
 
Qtron said:
A while back Briney Eye was quoting huge forces on the saddle, 700 lb plus, for 8 tpi threads in harder steels,, He had received a torque gauge but dunno the outcome of measurements.
Click to expand...
Sorry but still figuring out forum 'syntax' behaviour
 
Qtron said:
Pulleys would provide torque below 300 revs on graph?
Click to expand...
That can be misleading as the low RPM is pulling down the product. A theoretical stepper motor would have infinte torque at 0 RPM but in reality, it is limited by electrical characteristics. Looking at the torque vs. RPM curve, the torque is relatively constant at low rpm. At .001"/rev power feed @ 625 RPM spindle, the lead screw is only turning at about 8 RPM
Qtron said:
Full steps = Max torque, but far more prone to 'mid band resonance'. (Bench tested!).
Click to expand...
That's what I rememberas well. I am thinking that the lost steps I am seeing are the happening during the microsteps and the motor feedback corrects for them.
 
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