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Author Topic: Spindle Speed Control  (Read 2996 times)

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Spindle Speed Control
« on: March 22, 2009, 11:43:21 PM »
Hello All,

I am trying to get program speed control for a Chinese mill. The mill presently uses a potentiometer. I have a CNC4pc Speed control board and have it working on PWM. Here's my problem. I cannot find the right settings to give me good speed control. I can get it tuned from 500 to 2000 rpm and then from 2000-4000 is way off. If I get it tuned from 2000-4000 then the 500-2000 is way off. Also, I am not sure what function the "Increment" setting plays and I can't find anything in the manual that explains it. But, it does effect the speeds.

Can anyone help me with this? I am beginning to get frustrated after a week of "cut and try".

Thanks for your help in advance.

Bob Keyes
Kentucky
Re: Spindle Speed Control
« Reply #1 on: March 23, 2009, 01:00:59 AM »
Hello All,

I am trying to get program speed control for a Chinese mill. The mill presently uses a potentiometer. I have a CNC4pc Speed control board and have it working on PWM. Here's my problem. I cannot find the right settings to give me good speed control. I can get it tuned from 500 to 2000 rpm and then from 2000-4000 is way off. If I get it tuned from 2000-4000 then the 500-2000 is way off. Also, I am not sure what function the "Increment" setting plays and I can't find anything in the manual that explains it. But, it does effect the speeds.

Can anyone help me with this? I am beginning to get frustrated after a week of "cut and try".

Thanks for your help in advance.

Bob Keyes
Kentucky

Bob,

    It may be the nature of the beast.  The CNC4PC board will put out a linearly scaled voltage (voltage directly proportional to PWM duty cycle), while the motor controller may have a non-linear control voltage to RPM relationship.  Have you checked the voltage required to achieve specific speeds?  If it's not linear, then you're kinda stuck.

Regards,
Ray L.
Regards,
Ray L.
Re: Spindle Speed Control
« Reply #2 on: March 23, 2009, 09:15:20 AM »
Ray,

Thanks for your response. I checked it and it is linear from 1000 up. It is also linear from 200 to 1000. Looks like I will have to pick a range.

Thanks again.
Re: Spindle Speed Control
« Reply #3 on: March 23, 2009, 11:43:34 AM »
Bob,

    Or, do what I did - customize the post for your CAM software.  I wrote a post-processor to manage the spindle on mine.  The CAM program spits out G-code, with spindle RPM in the S words.  My post-processor parses the G-code, finds the S words, and figures out the best motor speed (I have a 2-speed motor) and pulleys to use to minimize the number of pulley changes, then adds code to prompt me to change pulleys/motor speeds when necessary, and changes the S words to the proper values to make the VFD run at the correct speed.  Doing that would allow you to have a linear command value in the S words in your CMA program, but generate non-linear S words in the actual G-code you run on the machine, so it works the way you want it to.  With a simple relationship like you seem to have, you could easily do the translation directly in the CAM post processor.

Regards,
Ray L.
Regards,
Ray L.
Re: Spindle Speed Control
« Reply #4 on: March 23, 2009, 05:13:50 PM »
Gosh, I think that might be over my head right now. I still don't know what the "increment" does on the speed control panel?? When you increase or decrease it what does it change??
Re: Spindle Speed Control
« Reply #5 on: March 23, 2009, 05:40:27 PM »
Gosh, I think that might be over my head right now. I still don't know what the "increment" does on the speed control panel?? When you increase or decrease it what does it change??

I think when you click on the up and down arrows, that DRO defines how much the S word changes.

Regards,
Ray L.
Regards,
Ray L.