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PM-935 Spindle Speed Sensor Location

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kb58

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I bought a Tachulator and needed a way to pick up speed on my PM-935. The Tachulator can also figure out cutter speed in inches per second once you input cutter diameter, which is a perk. There were several promising pick-off points, but all but one would pick up a speed signal that didn't match the spindle. That is, the sensor could be mounted to pick off the pulleys, or the reverse gear, but they'd all give wrong readings. The only place that looked promising was at the top of the spindle, adjacent to the hex end. A wrench (or power drawbar) needs access of course, so it can't crowd that area.

Turning the spindle by hand showed that in addition to the drawbar, an inner race also turns, so that was promising. Better yet, around the outer edge is a large bearing/bushing with two small threaded holes. They're the locking screws for the back gear lever collar. Moving that lever lifts the upper spindle assembly up and down, so whatever goes there has to ride on that to maintain a constant gap.

The pictures show what I came up with. Not shown are the mounting holes, and still to do is mill a slot to run the wires to the rear, and adding a cover for the top, all to keep the wiring and sensor clear of wayward wrenches. Of course, someone's going to say, "why didn't you mount the sensor here instead and save all that bother?"
 

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Z2V

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Looks good there @kb58. Glad to see there is another tach option out there no that MachTach has stopped shipping.
What triggers the sensor on this setup?
 

kb58

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For the moment, half the spinning end flange is painted flat black. If it doesn't pick that up, the supplied paper pattern will be glued on. The detector is infrared, so there shouldn't be any issue with stray light.
 
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mksj

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One other option is the bottom of the spindle attached to the RAM. I have been using both inexpensive Chinese RPM meters with an 8 mm sensor or the now discontinued MachTach with a small hall sensor. Could also use an optical instead of the 8 mm sensor. I integrate these into a LED light ring. My two major gripes with the Tachulator is the size of the housing and the only option is an optical pickup which I have had some issues with in the past. Below is a 935 system with tach/led light ring that slides up on the spindle. As far as SFM, I find it more useful on the lathe as opposed to the mill. I have an ongoing lathe system, and I debeting as to adding the Tachulator (I used MachTachs in the past). Just can't get past the size of the enclosure for a simple tach. system. On the lathe some of the manufactures offer a feature in their VFD systems that provide constant SFM while turning.

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Cadillac STS

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For the moment, half the spinning end flange is painted flat black. If it doesn't pick that up, the supplied paper pattern will be glued on. The detector is infrared, so there shouldn't be any issue with stray light.
Does the Tachulator allow a choice of how many pickups around the spindle? Mach Tach does and mentions that instead of one pickup per revolution 4 or 6 equally spaced sensor spots would be more accurate. Would be in the directions of the Tachulator setup because you would need to tell the chip what you are doing.
 

kb58

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It allows for 1-16 black/white transitions per rotation and has one sensor input. I don't think multiple inputs will work since if they're in parallel, only the first transition will be counted by the sensor.
 
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kb58

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One other option is the bottom of the spindle attached to the RAM. I have been using both inexpensive Chinese RPM meters with an 8 mm sensor or the now discontinued MachTach with a small hall sensor. Could also use an optical instead of the 8 mm sensor. I integrate these into a LED light ring.
Yes, I looked there but for some reason didn't think it would work—it obviously can, and since I also plan to add a light ring, I'll revisit the idea. A Hall effect sensor makes a lot more sense than an optical setup, given the dust and chips. But I also realize that flying steel chips could end up stuck to the magnet, though probably unlikely if it's embedded as you've shown.

[edit] Your attached figures on your post above are extremely helpful, thank you very much!
 
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kb58

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While the tachulator unit works fine with its optical pickup, I want to try a Hall sensor like you (mksj) are using. It just seems like a more reliable way to trigger the sensor. I asked the tachulator seller—twice—whether a Hall sensor would work, but no answer. That sort of bugged me because it takes about 5 seconds to reply with "yes" or "no." Maybe his thinking is, "I don't support that so you're on your own." Okay, I'm an EE and will try it anyway.

Hmm, I just realized something, that at high speed, the unit counts transitions, but at low speed, the unit calculates RPM by measuring the time between edges. Depending which edges it's using, an optical sensor may not work at low speed. Guess I'll find out. If for some reason it's a bust, the inner ring can always be painted black/white.
 

Cadillac STS

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Here is the manual for the Mach Tach.

It shows that there is a jumper to place to use the Hall Effect sensor. I think it lets Mach Tach board send 5 volts to the sensor. Since you are an EE you might be able to trace the circuit back and see how they do it to adapt to your application with Tachulator. And let us know how to do it in case someone else wants to know.
 

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mksj

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I also sent an email to the company that makes the tachulator regarding use a hall type sensor in addition to a few other questions, and never heard back from them. Probably will loose my business. The design of the PC board is also a waste of space if you mount it in a panel. At the end of the day I will probably use one of the generic tachs, I would love to put in a MachTach on my current lathe but alas they are no more. :cold:

On my last system build that I used a MachTach on, I substituted a generic 10 mm NPN hall sensor (NJK-5002C or NJK-5001C which is the 8 mm body) and it worked fine instead of the hall sensor he provided. The jumper on the MachTach used with the IR sensor was for the current limited 5V. The NJK-5002C worked without the jumper despite having a working voltage of 6-36VDC. I am disappointed with the tachulator that there is essentially no manual or Q&A on issues like use of hall sensors or anything else. At the price they charge for the units you would think there would be some technical support.
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