Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: bobkeyes on March 22, 2009, 11:43:21 PM

Title: Spindle Speed Control
Post by: bobkeyes 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

Title: Re: Spindle Speed Control
Post by: HimyKabibble on March 23, 2009, 01:00:59 AM

Quote from: bobkeyes 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

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.

Title: Re: Spindle Speed Control
Post by: bobkeyes 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.

Title: Re: Spindle Speed Control
Post by: HimyKabibble 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.

Title: Re: Spindle Speed Control
Post by: bobkeyes 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??

Title: Re: Spindle Speed Control
Post by: HimyKabibble on March 23, 2009, 05:40:27 PM

Quote from: bobkeyes 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??

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

Regards,
Ray L.