RPM sensor for Logan 400. Any bright ideas?

The MachTach is compact, works well, and you can program the teeth very easily. I would not know how to modify the $20 ones for the number of teeth, and you might get into limitations of maximum number of pulses per counting period, as the default is 1 pulse (range per counting interval). There are counters with scalers, but at the end of the day probably be close to the MachTach price. I rarely use the SFM on my lathe, but the MachTach would be plug and play. Like the use of a gear tooth pickup on this type of lathe.
 
Matthew:

I don't have a model 400, but wondering if you might have the same sort of spacer on the spindle that the model 200 uses to locate the rear bearing. On the model 200, there's almost 3/4 inch gap along the axis of the spindle between the headstock casting and the inside edge of the gear driving the reverse tumblers. The spacer on the spindle itself could be swapped out to add magnets, reflective tape or maybe even a disc for a slotted IR pickup.

If you don't want to drill holes, consider a split ring to replace the rear dust cap and use a setscrew to push it open and lock it in place.

Not sure if these are really practical ideas as I know almost nothing about the sensors themselves, but please keep us posted on your progress. I'd sure like to have a tachometer, and would like to see how yours works out.

TomKro
 
A quick update.

I went with the inexpensive readout and mounted the sensor as shown. IT was harder than i ever imagined to get the wire to the sensor in a way that would not leave it exposed. Worked that out and fired it up but the sensor did not read. Not sure why yet. Just get flat lines on the read-out. Anyways. Not looking for help yet as i have not really tried hard to figure it out but moving forward VERY slowly.
 
So a few comments that might help. To use this type of sensor you need to incorporate what is called a pull up resistor that connects between the 12VDC power (Red) wire VCC (pin 1) and the sense Vout (pin 2), usually something on the order of 1K ohm 1/4W is used for a 12VDC supply. In addition they require a small 0.1 uF capacitor (film like 50 or 100V) between VCC (pin 1) and the black GND/negative power supply Vout (pin 4). They also show a small capacitor CL between lead 4 and 2, this is specified as 4.7nF. See Pg3 and Pg11 of the spec sheet. The head of the IC has to be in the correct orientation relative to the tooth, this is shown on Pg5 of the spec. sheet.

ATS667.jpg

The other issue that the inexpensive tachs do not have the ability to do is set the number of teeth or poles per revolution, as such they will only work if you have a gear with 1 tooth per revolution or they sense one magnetic pulse per revolution. The MachTach you can set the number poles/teeth per revolution up to 90, which is a requirement for a gear tooth sensor.
 

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I ended up with a MachTech unit. They have several sensor options and are easy to set up and use. Good guys to do business with.
I've used the SFM reading a few times, but...... I wouldn't buy the tach for that feature alone.
 
I guess i should update the group with my final solution.

After buying two cheap hall sensor units from ebay i finally gave up and went with the Machtech using the gear tooth sensor. This in and of itself was an adventure and i want to give a public and huge shout out to Henry at Machtech for the assistance in troubleshooting to get it to work. Henry is awesome and stands behind his kit above and beyond what most vendors do.

I am running my lathe off of a VHD and had 12V available. The easiest gear to get at was teh bull gear which has 80 teeth. I added the heat sink to the unit so i could run at 12V instead of 9V. That worked great. The biggest trouble i had ended up being interference on the power line from the VHD which did not manifest itself at first in the normal way.

The symptom was proper RPM readings up to about 900 RPM and then the system would flip out. The thought was that this was partially due to the large number of teeth i was using for the gear tooth sensor. To eliminate the VFD as the source I tested with a remote 9v power source but the problem persisted. Again thinking it was the large tooth count we clipped the "C9" cap on the board. I will not pretend to know the details of why though as at this point i was following directions. Doing this allowed the PRM to increase to about 1000RPM before flipping out. No amount of adjustment at the sensor would correct this.

At this point, i re-tried running on the remote 9V power and that was the breakthrough. That cured the problem indicating that the VFD was in fact originally causing interfearance. I installed the recomended filter and wala. RPM's through all ranges.

Again thank you Henry. Machtech all the way. Machtech for all.

Now if anyone wants to repeat this pain i have two slightly used hall efect sensor set-ups available... cheap. :)

Matthew
 
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