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Author Topic: How to understand Spindle readings? I am confused..  (Read 284 times)

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How to understand Spindle readings? I am confused..
« on: April 23, 2019, 04:13:21 PM »
Help I am confused and cannot find detailed references (in the manuals)

I am setting up a CNC Lathe with a PoKeys57CNC. 
My goal is to have a CNC based threading capability on my Sherline Lathe.  Hence.
I am using a Dyn4 servo controller and 400W motor to run the "spindle".

The servo is setup in Speed mode and I have it working with MACH4 I can increase / decrease the rpms etc.  This is done thru the Analog 0-10v pins.  The manuals got me this far. :)

My questions:
1) The "True RPM" is accurate, I tested with a Tachometer on the chuck.
  • How do I interpret the other numbers; Spindle RPM, Spindle Motor etc?  They do not seem the accurately align with true.
  • If enter PGM RPM the spindle speed changes BUT it is about 30% lower than the "true RPM".  How do I get what I enter to equal "true RPM", it seems there should be a correction factor somewhere to offset the 30%

Is there a "manual" or "chapter" that covers the spindle in more detail and covers the above?  I have not been able to find it.  Since my goal is threading I would really like to understand the spindle parameters much better.

Thanks in advance
Re: How to understand Spindle readings? I am confused..
« Reply #1 on: April 24, 2019, 09:38:33 AM »
I'll do some research and try to get back to you, but if you go to the diagnostics tab in the top right corner, it shows the full calculation of spindle RPM with DRO's for each piece of data and the math operators between them. This should be the easiest way to understand what it is doing.
Re: How to understand Spindle readings? I am confused..
« Reply #2 on: April 24, 2019, 09:43:54 AM »
According to the Mach 4 API:

- TrueRPM is the measured RPM from the motor index pulse multiplied by the feedback ratio (this is the speed of your tool)
- MotorRPM This is not the spindle RPM!!! It is the motor RPM without any ratios for ranges (pulleys), etc...
- CommandRPM is the current value set by the S code (will be non-zero even after M05)
- SensorRPM is the RPM of the spindle at the spindle sensor and does not include any feedback ratio.
Re: How to understand Spindle readings? I am confused..
« Reply #3 on: April 24, 2019, 09:44:16 AM »
Thank you I will look into that too, I did not know that was there.

Was able to get the PGM RPM to match True RPM this morning by manually adjusting a range max value.  But, I need to readjust the range for each new PGM I enter.





« Last Edit: April 24, 2019, 09:49:58 AM by irakandjii »
Re: How to understand Spindle readings? I am confused..
« Reply #4 on: April 24, 2019, 09:49:00 AM »
Thank you

It would seem that the problem is a calibration issue with the Analog Voltage supplied by the PoKeys and the response from the servo motor.

Not sure what to do about that.
Re: How to understand Spindle readings? I am confused..
« Reply #5 on: April 24, 2019, 09:57:07 AM »
Analog calibration is required across industry, most hardware will have some way of adjusting this. Haven't used PoKeys so I cannot comment directly there. I don't think the DMM DYN2 has software configuration for that. Alternatively you can adjust the Mach 4 gear ratios to accommodate this.
Re: How to understand Spindle readings? I am confused..
« Reply #6 on: April 24, 2019, 10:05:40 AM »
Thanks again, It would seem I am on the right track then.

I can pick an "informed" value for max range for each speed range I want and then select that each time.  Just seems a bit of a hack.

It looks like the "slope" of the actual Analog signal is different than Mach4's expected curve.   I get negative (-) errors at the high end and positive (+) errors at the low end.  Almost like Mach4 could use a "look-up" table rather than a formula.

I am using the DYN4 controller, I will look into it more.  I saw dead zones but nothing about slope.
Re: How to understand Spindle readings? I am confused..
« Reply #7 on: April 24, 2019, 10:23:08 AM »
I just received an update from the Mach4 team.   It seems this is normal behavior for the PoKeys57CNC.

Maybe I should consider changing that out...
Re: How to understand Spindle readings? I am confused..
« Reply #8 on: April 24, 2019, 04:03:34 PM »
Love my ethernet smoothstepper, no affiliation other than a happy customer. Great support from them.

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Re: How to understand Spindle readings? I am confused..
« Reply #9 on: April 25, 2019, 01:39:06 AM »

I am setting up a CNC Lathe with a PoKeys57CNC. 
My goal is to have a CNC based threading capability on my Sherline Lathe.  Hence.
I am using a Dyn4 servo controller and 400W motor to run the "spindle".

The servo is setup in Speed mode and I have it working with MACH4 I can increase / decrease the rpms etc.  This is done thru the Analog 0-10v pins.  .

1. To get a more linear relationship, you need to increase the PWM base frequency to about 120Hz
2. 10V may not be exactly 10V. You need to have one "ferrite sleeves" (chokes) each for the 10V cable and the analog ground. Put the wires though ferrite sleeve or core a few turns.
3. After that, measure the highest voltage you can get with a good multimeter. e.g. it may be 9.7V or 8.5V. Now try to adjust until you can get  exactly 10V. Without the ferrite sleeves or chokes, it is no point calibrating as the readings will be all over the place due to noise.
4. In my VFD, I can just set the top freq to 382Hz instead of 400Hz to get true rpm from my spindle using  M3 or M4 because my BOB cannot give me exactly 10V but only 9.55V.
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