Proxxon Spindle Speed

[justgary]

All -

OK, I take it all back. The Proxxon is much faster than it sounds.

Zephyr9900 (Randy) and I had a discussion about a week ago regarding the spindle speed of the Proxxon die grinder that Tormach sells as a high-speed spindle.

I rigged up a simple optical circuit using five volts, two resistors, and a QRB1113 optical sensor. By marking a stripe on the shaft with a silver Sharpie, I could get a good frequency reading on an oscilloscope when I held the sensor up near the spinning spindle.

The attached photos show the marks I made on both the Proxxon and a TTS holder. You can also verify my math by looking at the oscilloscope screen shots. Don't forget to multiply the frequency by 60 seconds per minute to get RPM.

The range of my Proxxon is roughly 7,500 to 22,000 RPM. Randy and I both agreed that it sure doesn't sound near that fast. It is also very RF noisy (as you would expect for an AC motor with brushes), and caused quite a bit of hash in my unshielded circuit.

The Tormach (Series II) is dead on at 1000 RPM (after doing the calibration outlined in the manual), but a bit over speed at the top end. I set the spindle for 5,000 RPM and measured a little over 5,200. That's less than 5%, and plenty good enough for me.

Regards,

- Just Gary

P.S. I hope that the specks I see at the very top in my main spindle photo are sawdust from the recent plaque project, but I'm not holding my breath. The things you can see when you take a photo...

[zephyr9900]

Great research, Just Gary! Thank you for doing it.

Your sensor is very similar to the QRB1134 that I use with my Tachulator digital tach, though unfortunately the Tachulator only goes to 10krpm.

I don't know what I was thinking though--I had in my mind that 20krpm was the same as 20khz. Idiot... Seeing your scope screen with the 367.6Hz gave me a That's almost exactly the F# above middle C.

So I just took my Proxxon in by our Yamaha keyboard. I have (or at least used to, when I studied piano) perfect relative pitch, so it was quick work to associate the Proxxon dial settings with musical notes, from which I calculated RPM.

Here's what I got (no-load speed):

"5k" setting - G#2 - ~104Hz - ~6200rpm
"6k" setting - A#2 - ~117Hz - ~7000rpm
"8k" setting - C3+ - call it 135Hz - ~8100rpm
"9k" setting - D#3 - ~156Hz - ~9300rpm
"11k" setting - G3 - ~196Hz - ~11800rpm
"16k" setting - C#4 - ~277Hz - ~16600rpm
"20k" setting - E4 - ~330Hz - ~19800rpm

My Proxxon isn't quite as enthuiastic as yours, Just Gary. I have replaced the nose bearing with a hybrid ceramic, which feels a little tighter than the original all-steel bearing. It would have been interesting to have done this with the stock bearing in place, if only I had thought of it then.

Randy

[justgary]

Randy -

When I first hooked up the scope, I set the sweep to .1 ms per division so I could measure the 1000 RPM main spindle as a sanity check. After I found the signal way out at 10 ms sweep, the sanity part of the sanity check clicked in... A 60 ms period *is* 1000 RPM! After that, everything got pretty easy. Good thing I had a calibrated standard so handy.

I like the piano method of calibrating your spindle. Now you know that your dial is close enough, and that it really does go as fast as advertised. Your problem now is that you have to hum a few bars before you start cutting.

The sound of the Proxxon has bugged me since the first time I plugged it in. It just doesn't sound that fast, but now I know better. I'm starting to trust it.

Now for my main spindle... it doesn't really even get warm at 5140 RPM, so I'm thinking about calibrating it up closer to 7000 to see how much warmer it gets. It's a cinch to change the value in the file.

Regards,

- Just Gary

P.S. What's the difference between a piano and a fish? I warn you, it's a groaner.

[zephyr9900]

Originally Posted by justgary Now for my main spindle... it doesn't really even get warm at 5140 RPM, so I'm thinking about calibrating it up closer to 7000 to see how much warmer it gets. It's a cinch to change the value in the file.

If you pull that off, Just Gary, it will pretty much push me over the top in buying a new VFD (though overall I'm not disappointed with my Old Skool VFD--I've backed off on the braking setting a little and getting much more consistent braking). 6krpm is the proper speed for a .250" cutter in brass, and would allow a decent depth of cut.

Originally Posted by justgary What's the difference between a piano and a fish? I warn you, it's a groaner.

Why, a 1978 REO Speedwagon album, of course!

Randy (aaaah, college days...)

[justgary]

Originally Posted by zephyr9900 Why, a 1978 REO Speedwagon album, of course!

Excellent. I had forgotten about that album, and I graduated from High School in 1978. I guess I'll move on to pirate jokes...

I think that 6K RPM would not be any problem at all. When I did the calibration by the book, I ended up slowing the spindle down a little bit. I'll play around a little tonight to see what's available in the calibration range. A 20% increase will get me over 6100 RPM.

You mentioned before about the brake not working with E-Stop. Mine has only done that one time, and I was surprised when it happened. It may depend on what Mach is doing at the time, because it should know when you hit E-Stop. Every other time I have hit E-Stop, the spindle brake worked like normal, and the spindle stopped in seconds. I don't remember what was different about that one time, but I remember that it was more of an E than the other times (I think it was when the set screw loosened and the endmill was diving deeper and deeper and about to hit the vise).

Regards,

- Just Gary

[justgary]

Well, as I thought, the values are simple to change. Unfortunately, the upper RPM is programmed as a maximum in the VFD controller (an Emerson Commander SK, which is an interesting little box). I didn't take too long snooping around it, but it looked to me like the maximum frequency programmed is 170 Hz, but the controller only hits 144.2 Hz tops (on its little display) wide open. It does that before you get to 5140 on the Mach display, by the way. It's more like 4900 to Mach, but I measured it again at an actual 5260 RPM or so. I think I'll calibrate that out, now that I know more about the calibration parameters.

Anyway, I'm not really interested in voiding my warranty, so I put it all back how I found it. The difference between 144.2 and that "maximum" 170 Hz is curious, however. Had it actually gone to 170 Hz, it would have peaked right at 6200 RPM...

Regards,

- Just Gary