Source for know RPM reading

[dbb-the-bruce]

Whats a good common source for a known RPM in the 100 - 5K RPM range. I only need one good well known source to check my point and shoot RPM meter. Not really looking for full calibration etc. just a sanity check.

 

[GeneT45]

200 rpm is common for a lot of gear motors and should be pretty accurate. Stepper motors with little/no load can be accurately driven to pretty arbitrary rpm.

GsT

 

[Jim F]

Optical Tachometer

 

[ChazzC]

Somewhere I have a 60Hz wheel thank can be used to check shaft speeds; give me a day or two to find it. Assuming you have a Fluorescent light you can attach a copy of the disk to a shaft (lathe or mill spindle?) and use that as a standard for your gun.


EDIT: You’re in luck, I was able to track it down (see attached).

 

[markba633csi]

If you have an old-timey record player you have 33 1/3, 45, and possibly 78 rpm
Not as accurate as the 60 cycle power though I'm sure

 

[mmcmdl]

Optical Tachometer

I know Starrett makes them .

 

[dbb-the-bruce]

Bingo on the disk thing - Was scratching my head to come up with something like it.

For all of those suggesting a digital tach - That's what I've got. It's probably fine but I want to make sure for this case.

The disk will give me a way to confirm the tach. I can put the disk on my variable speed mill spindle and use the disk for setting the speed. Then see just how much difference there is between the tach and the mills speed read out just for yucks. Hopefully proves that the tach is accurate.

I'm sure that the 60hz AC line is an accurate time base.

Thanks.

 

[ChazzC]

Probably close enough:

60 Hz AC Mains Frequency Accuracy Measurement

 

[dml66]

Something like this tach from Amazon might work: https://www.amazon.com/Tachometer-Icstation-Proximity-Conveyor-Inspection/dp/B0B63S2TSN

I've used these on my drill press and lathe, easy to implement. For the lathe, I've switched to a rotary encoder which is more accurate, but the spindle RPM difference between the two is a rounding error. Because the magnetic sensor samples only once per revolution, it's more accurate at higher speeds.

 

[Nutfarmer]

Any synchronized motor will be as accurate as the line frequency. Ie a clock motor. Line frequency is maintained to a high precision.