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RPM sensor for Logan 400. Any bright ideas?

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mjhenks

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#1
I recently built a VFD set-up for my logan 400. It has provisions for a RPM read-out but i am struggling to find a suitable location for the pick-up on the lathe without drilling a hole in the housing. I am trying to use one of the sensors that requires mounting a magnet to the machine

I have looked at:

Bull gear. No room to mount sensor.
Gear Train. No easy way to mount sensor and keep things safe. (close the door)
Drive pulleys. No place to mount sensor.

Any bright ideas?
What have you guys done who own 9b's, 1400's or 400's?

Thank you.

Matthew
 

wa5cab

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#2
I don't have a Logan 400 or a manual on it but do have the Logan specs booklet with photos (see in DOWNLOADS). You would undoubtedly have to drill two mounting screw holes but from the photo of the machine with belt cover lifted, it appears that there should be plenty of room under the cover and behind the bull gear for mounting a fair sized sensor. It of course wouldn't work with cover lifted but you certainly won't be cutting metal with the cover lifted.

Also, I would recommend a sensor with built-in magnet. This type will work with any steel or cast iron bull gear. And to figure out how much space there is under the cover, use a rectangular metal cup filled with modeling clay sorta as a dentist would take an impression. Maybe use double-sided tape to stick the cup to the inside of the cover, and then close the cover.
 

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#3
How about on the back side of the chuck? I've been thinking about that for my lathe . (I have a plain back chuck, so the magnet would go on the adapter.)
 
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AGCB97

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#4
Shoe-Goo, Goop, various other names is a secure, permanent way to attach things w/o drilling holes. It has become my adhesive of choice. Most kitchen cabinets nowadays are put together with something like this. Sticks to anything except the greasy feeling plastics
 

British Steel

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#5
Hi Matthew,

If the bull gear has space around the teeth, the ATS667 "gear tooth sensor" from Allegro is pretty cheap on EvilBay, has the magnet and some clever circuitry built in; it's about the size of a pea (other than the leads) and is pretty easy to mount (it needs about 2 - 4 mm spacing from the gear teeth and the leads need to stick out at 90* from them, parallel with the spindle axis - but you can bend 'em to suit the space as long as that's where they *would* point).
If you have a 60-tooth bull gear use an LED frequency counter rather than a tacho' (a few Local Currency Units from a nice gent' in China) it'll read directly in RPM and update faster than a tacho' module, if not 60 tooth you'll need to swap the crystal on the frequency counter board (scale the marked crystal frequency by the same proportion as the number of gear teeth Vs 60 to get the new frequency) - not a hard job and crystals are so cheap (from similar sources) that I bought a bag of 25 for less than the price of one locally...
Fitting it wasn't so difficult, but meant drilling and tapping a hole for 1/4 BSP to put a piece of tube through, the leads were brought to the outside world via a 4-pole headphone socket (so I could run 12v, 0v and two sensor outputs in quadrature, future planning!), and a piece of PTFE was push fit over the tube and milled to take the sensor and follow the curve of the gear. If the headstock wasn't buttoned up I'd add a pic... I'll attempt a sketch when I get a few minutes :)

Dave H. (the other one)
 

mjhenks

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#6
Thank you for these ideas.

I think the idea by Robert and Dave are similar. I am looking into that but would appreciate a sketch Dave if you can. FWIW the Bull gear on a Logan 400, 1400 and 9B is the LP-1221 and has 78 teeth so sounds like some changes to the AST667.

Anyways, these ideas sound like they have a chance to fit over the other one i was trying.

Matthew
 

mksj

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#7
I would suggest you look into the MachTach, they also sell the AST667. You can set the slots/pulses on the MacTach for the number of teeth, it will also give you SFM and a few other functions. You could tap a small bracket off of the bearing cap or mount it off of the headstock, depending on what you use it will determine the location or just clean the surface and use some metal JB weld. A gear tooth counter would work well also, but you could also mount a small magnet to the shaft with some JB weld epoxy. If the latter, you could use any of the inexpensive evil bay tachs. I built the 1/2 sized MachTach and put it in a diecast Hammond box. Have not seen a VFD that has a separate input for a external sensor RPM, usually there is a scaler that gives the motor RPM based on Hz x scaler factor.

http://www.machtach.com/Docs.html
http://www.ebay.com/itm/4-Digital-R...all-Proximity-Switch-NPN-Sensor-/252701087303

Sensor pickup points for magnet or Gear Tooth Sensor. MachTach AST667 Gear Tooth Proximity Sensor and Cable Kit
Logan 400.jpg Gear Tooth Proximity Sensor and Cable Kit.JPG
 

British Steel

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#8
A very simplified sketch of the pickup "follower" I knocked up in about 10 minutes*, the 1/4 BSP fitting had to be drilled out a little to take the 10mm OD tube, the olive in the compression half of it was slit and locks the tube in place.
The recesses for the ATS667s were milled a little deep to ensure that they were held *just* clear of the gear teeth when the follower was pressed against the gear and the hole for the tube was left a touch undersize (3/8" drill, pressed in) so the tube and follower rotate nicely and lock in place by nipping up the compression fitting (that in turn is threaded into the rear bearing housing).
Spindle tacho pickup.PNG
I hope that helps someone :)

Oh, the use of two sensors, aligned to tooth and space gives 90* quadrature outputs, so as well as speed you can get direction - and the ATS667 is a "zero-speed" sensor so gives a count from stationary up to several thousand RPM and relative rotation, I'm thinking about indexing and possibly electronic leadscrew in the far, far future!

Dave H. (the other one)

* The follower, not the sketch!
 
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mjhenks

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#9
MKSJ.

The product in your second link is exactly the sensor and reader i have in hand.

http://www.ebay.com/itm/4-Digital-R...all-Proximity-Switch-NPN-Sensor-/252701087303

The read head is so large i am finding trouble mounting it anywhere safe as well as mounting the magnet. The best thing i have found is to mount the magnet to the chuck and bring the unit up from the rear. I am too thrilled with this idea.

I am liking the tooth counter idea best right now and will look tonight for a suitable place on the 400.

Matthew
 

mjhenks

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#10
Looked over the lathe last night and learned a few things.

1. Bull gear is the only place to put the ATS667 style sensor. If i used the gears towards the tail end of the head stock then when you engage the back gear you no longer know the spindle RPM.

View media item 96760



2. The bracket i made for the "other style" hall sensor when turned around just happens to align with the back side of the bull gear. Good for me.

View media item 96757
View media item 96756
3. The readouts mentioned above (ebay and Machtach) should adapt into by VFD box easily.

View media item 96758
View media item 96759
Sounds like i just need to decide which one.

Is it worth the extra money (about $25) to get the readout options that the Machtach offers? Same sensor, same form factor but allows switching from RPM to SFM.

http://www.machtach.com/Gallery.html#

Matthew
 

mksj

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#11
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.
 

TomKro

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#12
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
 

mjhenks

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#13
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.
 

mksj

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#14
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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ch2co

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#15
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.
 

mjhenks

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#16
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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