Flat lap for rock polishing

These parts will assemble a working flat lap for rock polishing. The assembled parts drop onto a standard 5 gallon bucket to hold the drip water. It uses inexpensive 6” or 8” diamond disks and is driven by a 12 volt DC motor, all of which can be purchased from Amazon. It is assembled with eight 3-1/4” stainless steel machine screws and nuts.

The longest part is 10” which will have to fit diagonally on your bed.

The slots in the side supports were made to fit a bucket rim that measures 11-1/8” ID and 11-3/4” OD.

One critical part is the disk support that fits on the motor shaft. This has to be a snug fit to prevent wobble. The motor shaft is 8mm, which is just about 5/16". But the exact size of a printed hole is uncertain and may depend on the material you print with. I used carbon infused PLA which tends to make a smaller hole. The same part printed in straight PLA is likely to be looser. So your first print should maybe be this part and fit it to your motor to verify you can get smooth rotation at speed. I used a 5/16" drill bit to clean the hole and it was still a very snug fit. 

The disk support is held to the motor shaft with a 6-32 machine screw. You may need a 6-32 tap to clean the printed threads. 

The printed nut that holds the diamond disk to the disk support has a 1/2-13 printed thread. Depending on the material you use, this may be hard to turn. One trick you may use is to coat the threads with automotive polishing compound to burnish the surfaces and make a better fit. Or you may scale the X and Y (but not the Z) dimensions of the nut in your slicer to 102% to loosen the fit.

If you wish to print the water bottle you’ll need a valve for it. I used a 1/8” pipe thread needle valve. The cup STL has threads for 1/8" pipe, but they may need to be cleaned up with a tap to use them.

The bottle shelf is held to the bucket with a 1/4-20 hex bolt, and you may need a 1/4-20 tap to refine the printed threads. The small knob is to fit over the head of the 1/4” hex bolt.

You’ll need a 12 volt power supply of at least a couple of amps to run the motor. I don’t use variable speed. The full speed of about 3,000 RPM seems fine.

Motor
https://www.amazon.com/dp/B0B221MQLC?th=1

8” disk
https://www.amazon.com/dp/B08TB9KX25

6” disk
https://www.amazon.com/dp/B08BF8MZC1

Needle valve
https://www.amazon.com/LASCO-17-1901-8-Inch-Female-Straight/dp/B008E33AIO/

You’ll also need a 12 volt power supply of at least a couple of amps to run the motor. I don’t use variable speed. The full speed of about 3,000 RPM seems fine.