[g29cc]

Well I bought a photo tach this weekend and just checked a few of my machines.

NM200 series 1

1000 rpm on Mach3 was 1029 rpm on tach , 1049 on the VFD behind the machine

2000 rpm on Mach3 was 2036 rpm on Tach, 2040 on VFD

3000 rpm on Mach 3 was 3019 rpm on tach, 3035 on VFD

4000 rpm on Mach 3 was 4029 on tach , 4049 on VFD

So it seems that I got mine dialed pretty close to what it actually is on the vfd/mach3.

Just thought I would add that incase anyone else is curious.

[doorknob]

I am curious about the photo tach - which model and mfg. tach did you get, and did you put a reflective tape onto the spindle or on a tool or somewhere else? How repeatable is the reading?

[g29cc]

It was made by Cen Tech. I don't have the box in front of me for model #. But it was from Harbor Freight.

The rpm varies by a few rpm. Say +/- 5 rpm maybe. Way more accurate then you need really for a machine like this. I took a couple readings and some of them where the same each time. So I believe it was quite accurate for how much it cost and what it was measuring.