Introduction: DIY Lathe Disc Sander
This is an indispensable tool (a disc sander) made from another indispensable tool (a lathe).
Does this require a lathe? Yes. Maybe no. Do you have a motor lying around? Do you want to use a drill instead? A drill will be underpowered, but if anyone can make it work, I'm sure it's you.
Do you need any special tools to make this? No, not really. Except that if you're using a lathe, you'll need a faceplate. But good news is, most lathes either come with one or have one readily available.
Step 1: Make the Parts
Cut the following parts with a table saw, a track saw, a circular saw or jigsaw with an edge guide, or even a hand saw:
-  14" x 14" disc blanks
-  15-5/8" x 9-1/8" table blanks
-  5-7/8" x 5-3/8" box sides
-  13" x 5-3/8" box front
-  13-1/2" x 8-7/8" box bottom
Note: you can absolutely make these parts on your own; the plans I have available on my website will show you how to nest these parts into a 4' x 2' with minimal waste.
Step 2: Cut the Notches in the Table Blanks
Make a long cut in the table blank, leaving just two inches in-tact at one end of the board. Crosscut a smaller notch in Table Parts B where the long cut ends to separate the waste piece. Repeat for both boards.
Note: If you're doing this with a tool with a circular blade blade, you may have to use another tool, such as a jigsaw or handsaw, to free the waste piece. This is because a small part of the wood will still be connected due to the blade's shape.
Step 3: Glue Up the Table and Disc
Laminate the two disc blank pieces together with wood glue, and clamp until dry. Alignment of all of the edges isn't critical, but it's good practice anyway.
Laminate the two table parts together just like you did with the disc blanks. Same rules apply, although take care to align these two a little more carefully than you need to with the disc blanks.
Step 4: Route the Disc With a Circle Cutting Jig
Mark the center of the laminated disc blank with a sharp implement like an awl, then drill that punched mark with a small drill bit (I used a 3/32" bit). Be sure to not drill through the entire disc.
Using a router, a straight-cut or spiral upcut router bit, and either a shop-made or commercially available circle-cutting jig, route a 12" diameter circle (6" radius) from that center point.
Note: in the video above, I show you how to make a simple circle cutting jig with one of the waste pieces from the 4' x 2' sheet.
Note 2: It pays to take this slow with the router, 1/4" at a time.
Step 5: Make the Shroud
If you followed the directions, you should have an in-tact waste piece from the disc blank that looks like a square with a big hole in it. Rip it at 5-1/4" to release a shroud.
Step 6: Prepare the Disc
Attach your lathe's faceplate to the center of the disc. The center hole you drilled earlier will come in handy as a reference point. Secure the faceplate with as many screws as it will accept. You can now attach sandpaper to the front of the disc.
Step 7: Assemble the Box
Mount the shroud to the side of the box bottom, then mount the sides and the front with screws. It's pretty important to pre-drill here so you don't split the edges of the plywood.
Step 8: Attach the Table
After the box is assembled, you can attach the table. You may need to shim it — masking tape, small wood shims, and even paper or cardstock are good methods for shimming the table. The end-result should be square to the disc when both are mounted on the lathe.
Step 9: Clamp Down the Box and Start Sanding
The easiest way to get started is to simply clamp the box down to the lathe. Now you're done — go make some wood dust!
Note: You can optionally add a lock to the bottom of the box to hold it down to the lathe bed. I did on mine, but I do have enough clearance on the underside of the lathe to reach a lock.
Note 2: You can also add a dust port to the bottom of the box if you have clearance for a vacuum hose. Otherwise, you can clean out the box with a vacuum manually, as most of the dust gets trapped inside anyway.