# PM932



## Plas62 (Sep 9, 2013)

In the manual (HaHa) on my new PM932 it indicates that the speeds shown on the face plate are RPM's. On the face plate itself it has a symbol that I believe means that they represent sfm. Does anyone know which it is. Has anyone used a handheld tachometer to measure the speed of each of the 6 gear settings, if so would you mind posting the results. Below is a pic of the face plate.


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## Ray C (Sep 9, 2013)

Yes, those are RPMs on the front plate... Something to keep in mind though.  AC motor RPM is impacted by line voltage and it's not very linear.  My house voltage usually varies between 117 and 123 volts throughout the day in normal weather in the summer heat when everyone's AC is running, it drops down to 112 sometimes.  Since the gears produce a ratio, small changes in motor RPM can make big changes at the spindle.  This true of all equipment -not just the 932.

I have a tach and will run out to the garage and check my PM45 mill.  


Ray


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## Ray C (Sep 9, 2013)

Here you go...  Actual line voltage during the test was 240.  Motor is rated for 220.  That's a 10% increase in voltage.

Actual reading vs label, %delta

119 vs 90, +32%   (note, below limit of electronic tachometer specification of 150 RPM).
212 vs 210, +1%
356 vs 345, +3%
689 vs 670, +3%
1219 vs 1180, +3%
2030 vs 1970, +3%

I'd say it's about dead on!  As soon as you apply a little load, it will drop a few percent no doubt...  

BTW, this is with a PM45 but they have exactly the same internal gearbox and gears.

Ray


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## R2.0 (Sep 9, 2013)

Ray I believe you are mistaken. AC motors typically run at a set speed, generally some multiple of the line frequency. Voltage will affect the effective horsepower of the motor, which may make the motor bog easier, but that isn't really speed as much as load.


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## Ray C (Sep 9, 2013)

In practice, I think you will notice a small variance in RPM with changes in line voltage.  At extremely low voltage the motor won't turn but once it starts, it will somewhat get up to speed but, slip will be very high.  With full voltage, there will be less tendency to slip and you'll see several percent variance (increase) in RPM.


Ray



R2.0 said:


> Ray I believe you are mistaken. AC motors typically run at a set speed, generally some multiple of the line frequency. Voltage will affect the effective horsepower of the motor, which may make the motor bog easier, but that isn't really speed as much as load.


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## Plas62 (Sep 9, 2013)

Thank you very much Ray for the quick response. That is what I needed.

Jim


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## 7HC (Sep 10, 2013)

Plas62 said:


> In the manual (HaHa) on my new PM932 it indicates that the speeds shown on the face plate are RPM's. On the face plate itself it has a symbol that I believe means that they represent sfm. Does anyone know which it is. Has anyone used a handheld tachometer to measure the speed of each of the 6 gear settings, if so would you mind posting the results. Below is a pic of the face plate.



It's a pity that the small DRO in the bottom left of the face plate only measures spindle position and not spindle RPM as well. 
Is anyone here smart enough to figure how to add that feature?

M


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## Ray C (Sep 10, 2013)

No easy way that I know of, unfortunately.  Somewhere you need something that generates a tach pulse based off actual spindle RPM.  On all my machines, I use those cheapo tachometers that work with a piece of reflective tape...





7HC said:


> It's a pity that the small DRO in the bottom left of the face plate only measures spindle position and not spindle RPM as well.
> Is anyone here smart enough to figure how to add that feature?
> 
> M


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## R2.0 (Sep 10, 2013)

Hmm. I learn something new every day.


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