Power supply question

[jhowelb]

Ok, here is the existing set up. Two Geckos connected to two Kelling 495 oz in steppers rated at 3.6vdc operating a 9x20 lathe.


Heard it suggested that power supply voltage should be 20 to 25 times motor voltage. (72 to 90) Currently running on a 40vdc transformer.

Mach 3 turn tells me I can't thread at 2000 rpm on the spindle and sure enough when I try a "dry run" the motors squeal and lose power and move not.

The question. Can I expect better performance if I swap the transformer out for say 72vdc?

[neilw20]

Look closely at the specifications for your stepper driver modules. Do you intend to find the thermal limits.
It's easy to get the smoke out. Hard to get it back in again!
The setup of these and setting the Mach3 configuration is most important.
I have had a stepper platform move at 25000mm/min which is 16"/second.
My normal operations rapid at 2500mm/min which is 10% of the above.
I have observed other machines at 5'/second.
It is all in the setup and careful design of the control system.
As you increase your resolution/step your maximum feed rate reduces.
To thread at 2000RPM the tool has to be able to accelerate to the correct feed rate before starting the cut, and has to be able to stop at the end of the cut.
Get your feed rate limits and tuning setup before you try doing fancy things.

[LeeWay]

I have these motors and that size PS, both from Keling. You motors will run faster and have more torque with the higher PS. I ran these using a 48VDC ps initially.
You can also set your frequency higher if your computer can handle it. That may also give you a higher speed range. Don't forget to tune those Gecko's either. They will just purr for you.
Switcher is right. You need to optimize all your settings and tuning in order to see just what they can do.

Why do you need 2000 RPM on the steppers for threading?
I might could see that on a high speed lathe, but all the threading I have done on my little 7/12 has been relatively slow. I am installing my motors on this today BTW. Thats why I ask.
It is only running with that 48 VDC PS and 201's on some 269 oz motors.
There is a high step count on these though. 52,000 I think on my tailstock.

[neilw20]

Hi LeeWay,
I think he means 2000RPM spindle, not stepper, and my names is:
Neil.

[jhowelb]

2000 rpm spindle is correct, and the need is to produce a smoother cut and smoother thread. At slower speeds the thread looks ragged as if it were ripped out.

Steps per rev are fixed to the pitch (0.200 inch) of the ball screw, no tuning possible there. Increases in acceleration start the squeal sooner. Slower velocity would be counter productive and faster results in squealing on rapids.

Will I smoke something at 72 volts?

The only resolution I can see is to improve the stepper performance at higher speeds Ergo: higher voltage.

[neilw20]

Originally Posted by jhowelb 2000 rpm spindle is correct, and the need is to produce a smoother cut and smoother thread. At slower speeds the thread looks ragged as if it were ripped out. (Instead of going faster, put a small z increment for each threading pass so the tool cuts on 1 edge. Z step = 1/4-1/2 X step for each pass.) Steps per rev are fixed to the pitch (0.200 inch) of the ball screw, no tuning possible there. (Leave more room in Z. Start further away from job to alow more space to accelerate. Maybe a G1 Z move followed by threading The Z axis has to be synced to the spindle and cannot accelerate instantly.) Increases in acceleration start the squeal sooner. Slower velocity would be counter productive and faster results in squealing on rapids. Will I smoke something at 72 volts? (LOOK AT DRIVER SPECS, or MAKE some SMOKE. Trial may lead to error) The only resolution I can see is to improve the stepper performance at higher speeds Ergo: higher voltage.

Make more chips, less smoke.

[LeeWay]

Originally Posted by neilw20 Hi LeeWay, I think he means 2000RPM spindle, not stepper, and my names is: Neil.

Opps. My apologies Neil.
Thanks for the clarification.
You will get better speed and performance @ higher voltage on these motors. Whether that is good enough, I am not sure.
I am using this setup on a mill with 203's. I can't rapid but 200 IPM on my Z. It weighs about 70 pounds or so. 30 to 35 Kg. I can run them @ 350 IPM on X and Y, but this is linear ways and ground ball screws. No real way to tell if they are going to thread for you like you want.