RPM sensor for Logan 400. Any bright ideas?

mjhenks

Active User
Registered
Joined
Feb 5, 2014
Messages
198
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
 
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.
 
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.)
 
Last edited:
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
 
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)
 
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
 
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.jpgGear Tooth Proximity Sensor and Cable Kit.JPG
 
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!
 
Last edited by a moderator:
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
 
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.

headstock.96760

headstock.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.



3. The readouts mentioned above (ebay and Machtach) should adapt into by VFD box easily.



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
 
Back
Top