This is part 2 of our three part series about building a Lathe Disc Sander. Here's a link to Lathe Disc Sander, Part 1, if you missed it.

The lathe provides the motor and frame for our disc sander, so all we really need to build is a platen to hold the sanding disc and a table to support the parts being sanded. The key to an effective disc sander is the platen spinning true with no wobble or shake. Using 3/4" thick MDF makes this pretty easy to accomplish. A circle was marked out on the MDF a little larger than the sanding disc, and then cut out on the band saw. The lathe shown here has a 6 inch “swing” over the bed, so I am using 12 inch sanding discs. But 2Sand.com has discs available from 8 inches to 24 inches in diameter, so you can get the right size to fit your lathe.

A face plate is screwed onto the MDF disc, carefully aligned to the center point of the circle. I had an extra 4” face plate that I used. I have never had problems with this, but if you are buying a dedicated plate, getting a larger one won’t hurt. The mounting screws should be as long as possible but also of a large enough gauge to fill the holes in the face plate. This will help eliminate any movement. Most face plates use #10 or #12 screws.

Mount the assembly to the lathe and set up the tool rest to cut the edge of the stock. Start at a low speed, we know that this assembly is out of balance. Cut the edge of the platen until is it smooth all the way around with no flat spots, and is no bigger than your sanding disc. It may well end up slightly smaller than the disc, mine did. This is fine; the discs can always be trimmed to fit.

The tool rest is then repositioned and the face of the platen is flattened. MDF is usually pretty flat, but any variations in the material or the face plate need to be removed for best results. Carefully true the face so that it is as flat as possible. Setting the tool rest close to, and parallel with the platen helps guide your work. Use a good straight edge to check across the face as you work, mark any high spots, and then shave those down. When properly prepared, the platen should spin smoothly with no vibration and no oscillation at the face.

The sanding discs are attached with pressure sensitive adhesive (PSA), so I took the time to laminate the face of this platen to make changing discs easier and keep the MDF from being damaged. Alternatively, several coats of varnish can be applied to the platen or a separate MDF disc can be made for each grit. The best part about making your own tools is that you get to choose the best options for your needs. Watch for the next blog post where I will be sizing and building the work table for the disc sander and adding a miter slot.