Logan Lathe 11 Inch Tachometer Mount

This is a hall effect tachometer mount for the logan lathe.  My goals in this build were to have the tachometer holder be as visually and mechanically unobtrusive as possible.    This mounts completely inside the spindle housing, does not get in the way of any attachments or gears, and does not require any permanent modifications to the lathe.  Just need to swap two slightly longer screws that hold on the motor hanger.  

This fits a logan 1922.  It may fit on other 900 and 1900 series models but not sure.  Big key is if the motor mount bolt holes go all the way through from the backside into the spindle cavity.  The shape of the spindle chamber casting will matter as I snugged the holder in the back corner and it fits somewhat flush to the curve of my machine.  Not sure if the castings changed for different years or models of the 11".

This was created to fit a "DIGITEN 4 Digital LED Tachometer" found on amazon but any M12 sized tachometer sensor should work fine.

The magnet that came with the sensor was very wide so I used a different one.

This is only a sensor holder, and I did not include a housing for the display.

ACCESSORIES:

1 - 12mm hall effect tachometer

1 -  ½" x  1/8" round magnet (not the magnet that came with the sensor)

2 - M3 x 8mm Flat or Oval Head Screw

2 - M3 Nuts

2 - ¼" x 1 ¾" Socket Head Bolts (2" would work)

2 - ¼ Nuts

CA Glue (super glue or other appropriate glue)

Zip Ties to secure the cable

ASSEMBLY:

1 - Print all parts.  Mount is the only one that might need supports.

2 - Glue the ring flush to the front edge of the circular indent on the top of the mount.  The back side of the ring should register against a lip on the mount.  

3 - Replace the bolts on the left most motor mount with longer 1 ¾" bolts.  They should protrude through into the spindle cavity without getting anywhere near the spindle itself.   This is most easily done by replacing one bolt at a time so you always have one bolt holding the motor mount.  Probably would not be a bad idea to support the motor mount arm with some wood blocks.  The bolts should be protruding about 3/8" to ½" into the spindle cavity.  You do not put the ¼ nut on at this time.  It is not needed to support the motor only the tachometer holder.

4 - Place the tachometer holder into the back left corner of the spindle cavity in front of the two now protruding motor mount bolt ends.  Push the holder towards the back of the lathe and onto the two bolts.  This can be a bit fiddly because there is not much room to maneuver and see but you can use the top lip of the mount which should just fit on top of the back cavity wall just above the two mounts.  Push it all the way back as far as it can go so its fully seated against the cavity wall.  The bolts should protrude slightly from the front of the holder.

5 - Place the ¼" nuts on the bolts to secure the holder.  This only needs to be slightly tight.  Dont crack the holder.  I actually only put on one bolt because the holder was tight on the bolts already and it was hard to get to the bottom most bolt.

 6 - IMPORTANT Figure out which side of the magnet activates the hall sensor correctly.  The polarity matters, at least it did on mine.  You will probably need to get the electronics on your sensor setup fully to test.  Follow the instructions from the manufacturer.  Mark the correct side with a piece of tape or sharpie.

7 - Mount the magnet into the spindle magnet holder half that has the opening for the magnet.   Make sure the correct side (found in step 6) is facing outwards in the holder.

8 - Place the M3 nuts into the nut cavities on the back of both sides of the spindle magnet holder.

9 - Place the two halves of the spindle magnet holder over the spindle to the left of the very last gear.   The alignment needed between the two pieces should be obvious. Make sure that it's pushed up snug next to the gear.  This should give clearance on the left side, so it does not touch the housing.  Spin your spindle a few times to make sure there is no rubbing.

8 - Carefully thread in the two M3 bolts to the hole on each side of the spindle magnet holder.   They should engage with the nuts.  These only need to be slightly snug. 

9 - The hall sensor should be threaded along its length have two thin nuts that come with it.   Remove the front nut on the hall sensor if the nuts are on the sensor or place one of the nuts on the sensor if they came separate.  The nut that's on the sensor should be nearer to the back of the sensor but exact position does not matter as you adjust them in step 10.  Place the sensor through the ring on the mount from the back so the sensor end is facing the spindle.   Thread the remaining nut onto the front of the sensor until hit presses up against the front of the ring.  Just needs to be snug.  There should be one nut on each side of the holder ring keeping the sensor in place.

 10 - Adjust the two nuts on the sensor to put the sensor tip close enough to the magnet holder to register.   As you can see from my pictures it did not need to be super close.  I think mine has about 1/8" spacing.  This probably depends on the sensor itself if you used a different brand than I did but they are probably very similar.

11 - Route the cable over the motor mount.  The rest of the routing will depend on where you are trying to put the tachometer display.  I run mine down and out the left side.  It's important that you make sure you secure the wire around any of the moving parts of the lathe that you have it go by with zip ties so it does not drift and get caught in any moving parts. 

12 - Mount your display somewhere appropriate.  You may need to get a box for the display (I think they can be found to print).  I did not include mine in the print as my setup is very specific to my VFD enclosure.  

13 - Connect the sensor to the display and the display to power. Make sure you keep any dangling cords zip tied for safety.