12" Disk Sander

12" Disk Sander

How I made it.

The motor:

1/2 Horse power induction, 1725 RPM, reversible.

As you stand, facing the disk, it must turn counter clockwise.

The base:

I built a box to raise the motor shaft to 6.5" above the base of the sander. This allows for a 12" disk and some wiggle room. The table top is set at 6.5" as well. When mounted, the disk must be 90 degrees to the table vertically and parallel to the table on the horizontal.

The disk:

The disk must be true and balanced. I first cut out a 12.25" disk from MDF on the bandsaw using a circle cutting jig. With the motor bolted down and V pulley attached, I used the table as the tool rest and trued the V pulley using a scraper. I then mounted the MDF disk on the lathe and turned a shallow 1/8" mortise sized to accept the V pulley.

I then drilled mounting holes near the hub of the pulley, leaving the actual V portion intact for use with the brake. I epoxied and screwed the pulley to the disk and mounted the assembly to the motor. Then mounted the motor and disk 90 degrees to the table vertically and parallel to the table on the horizontal.

True the disk:

with the power off, turn the disk by hand while holding a sharp scraper against the disk using the table as the tool rest. Starting at the outside edge continue to turn the disk by hand, removing material until the scraper contacts the surface for a complete rotation. continue this until you have reached the center. At this point the disk will not be balance and you may want to use a clamp to keep the sander from moving around. Now turn on the sander and use the scraper to make the disk round, leaving at least 12" of disk. use a sanding stick to finish flattening the face of the disk. Use a strait edge to verify the disk face is flat.

Balance the disk:

Turn a piece of hardwood 6" long to the same diameter of the motor shaft.

Remove the disk from the motor and press onto the end of the wooden shaft. Use your chuck as a counter weight. Place a 3" x 3" x 6" piece of wood on the lathe bed. The wood must be flat. Shim the wood until perfectly level.

Now set the disk / chuck assembly on the wood and let the disk roll until the heavy side stops at the bottom.

mark the location and verify that it always stops at the bottom. Start drilling holes in the back of the disk using tape on the drill bit to mark depth to prevent boring all the way through. Recheck the balance and repeat until the disk will stop rolling at random positions.

This may require 20 holes or more. Seal the disk with Deft, or shellac on both sides

The brake:

The brake is just a lever with a piece of V belt brad nailed to a block that will drag on the V pulley. I made a spring out of a thin piece of maple to keep the brake disengaged until needed.

Dust collection:

I enclosed the back of the motor pedestal and installed a 4" dust port. The air pulls in from under the table, around the disk and out the back.

Disk guard:

I used a 1/4" hardboard with 3/4" plywood ring to cover the outside of the disk, leaving the disk proud by about 1/8".

Fence:

I use a drafting triangle to set the fence square. I relocate the fence as the abrasive wears, setting it square before clamping.

Hold down:

I turned a handle and mounted a nail in the end, bent to 90 degrees.

Use the sander to sharpen the point. Is great for removing small pieces from the disk while keeping skin on your knuckles.

Abrasive disk:

The sander uses adhesive backed disks, up to 12" in diameter, some of the pictures show the sander with a 10" disk mounted

Jigs:

Jigs are just used to sand pieces square or at an angle. I installed a stop in the jigs to make each piece the same dimension.