Split Lap Conversion

Convert a generic bench polishing motor into a split lap machine for polishing jewelry or watches. 

Additionally if you print the lapping plate and attach a flat top sanding disc to the arbor you can do some minor lapping. Being plastic and using set screws it is not equivalent to a dedicated lapping machine but can get the job done in a pinch. 

I've designed this conversion to work with a standard 16mm diameter arbor and 3 inch diameter wheels. You could probably get away with larger work wheels but they might get snug in the shield enclosure. 

I've also included the STEP files if you have a different motor and you need to update the location of mounting points, arbor holes etc. 

For this build you will need the following:

• Bench top polishing motor - I purchased this one - Amazon
  • If you have another model i've included the STEP files so you can modify to fit your machine. 
• 4 - M3 x 10mm bolts 
  • 2 fix the lapping plate shafts to the unit and 2 are used as set screws for the lapping plate
• 6 - M3 Heat set inserts 
  • 2 for lapping plate
  • 2 for lapping plate shafts on the main body
  • 2 to attach the shield/backsplash to the body
• 2 - M3 x 12mm bolts 
  • Attaches shield/backsplash to the main body
• 2 - M4 x 20mm bolts
  • Attaches motor to Split lap stand

 Build Instructions: 

1. Start by using a soldering iron or other suitable tool to add the M3 heat set inserts to the stand. To start you only need the two on top that are used to bolt the shield/backsplash to the main body. 
   • Note: while the this printed surface is on an angle take note that the bolts still go straight up and down
   • You can also add the other 4 for the lapping plate at this step but they are not necessary if you don't intend to use it. 
2. Flip your motor over and remove the two bolts holding the black plate. 
3. Remove the arbor on the left side (side closest to the power switch) this will be pointing down when mounted and will need to be removed for clearance. 
4. Place the motor in the conversion stand right arbor facing up so that the power switch is on closest to the bottom and secure using the 2 - M4 x 20mm bolts. You may need to wiggle the motor up or down 1mm or so to get the bolts to line up, however at rest it should be pretty close. 
5. Lower the shield onto the main body making sure to align the Arbor shaft to the hole in the shield and once aligned and set in place, secure to the main body with 2 M3 x 12mm bolts
6. Secure the Split lap to a bench or table using your preferred method
   1. I have added holes in the base so that you can secure with screws
   2. My preferred method as seen in the photos is to secure with clamps as this is less permanent and easier to move after you are done.  
7. Add desired polishing/sanding wheel to your arbor and enjoy! 

Optional (Lapping Plate): 

1. Place lapping plate shafts in holes on top outer edges of machine making sure to point the flat edge of the shaft outwards on either side of the machine. Using 1 M3 x 10mm bolt on each side secure the shafts in place. 
   • Note: Each shaft has a hole going through them. The holes are meant to go on the bottom side of the shaft as the bolts securing them in place run through them. If the bolt does not fully screw into the body the shaft could be turned and the bolt might not be running through this hole. 
2. Set the lapping plate on the shafts with the shafts running through the holes on the lapping plate
   • Note: The cutout in the lapping plate is offset to align with the arbor so you need to make sure you put the correct side facing down so that the cutout aligns with your grinding/polishing wheel
3. Move the plate up or down so that it aligns with the wheel and once aligned, lock in place using the M3 x 10mm set screws on the outer left and ride side of the lapping plate. When properly installed the bolts will bolt down to the flat face on the shafts