My 6" Disk Sander
I made this disk sander out of a 1/4 HP motor that I had sitting around and a 2' square sheet of 5/16" plywood. (I picked up an whole stack of 2' squares for free at a garage sale.)
Step one was to slice the plywood into 8" wide sections. Two were cut down to 16" long and glued together, with the 8" square cut pieces in between them, to form an 8" x 16" x 7/8" board. (It should have been 15/16ths thick, but it wasn't.) Lots of C-clamps, binder clips, and lead weights were used to press them together.
To this I bolted the motor, a 1/4 HP General Electric motor built in the 4th century BC, with four 5/16" bolts. The heads of the bolts are recessed into the bottom of the board. Using a square, I carefully shimmed the base of the motor until the motor shaft was parallel to the wood base.
Next, I cut the remaining 24" x 8" piece of plywood into three 8" squares and glued them together to form an 8" square 7/8" thick. This was cut in half, to form a pair of 8" x 4" pieces. One of these became the table, and the other was cut into the supports.
I carefully measured the height of the center of the motor shaft above the base - it came out to 3-½". From this I subtracted the thickness of the table (7/8"), to get the required height of the supports: 2-5/8".
Since this was more than half of the 4" width available, the pieces were laid out so:
Cutting a 4" piece into two 2-5/8" pieces
This made two identical pieces. To make them even more identical (?) I clamped them together and sanded the top and bottom surfaces flat and even. Then two pieces were then screwed to the table, leaving a ½" overhang on each end. I made sure that the screws holding the table to the supports were accessible, as removing the table is the only way to change the sandpaper!
I put a 1/2" arbor on the motor - this is the metal contraption that fit on the shaft and provided a 1/2-20 UNF thread. I think it was originally a piece of a grinder. I cut two disks of 1/2" plywood, glued them together (this probably wasn't necessary), and carefully drilled them 1/2" to fit on arbor. After tightening the bolt securely, I carefully traced the outline of the arbor on the table and cut it out. This let me recess the arbor halfway into the table and put the table on the exact centerline of the disk.
The last step was to screw the table to the base and true the disk with a chisel. As I did, I found that the sander wanted to wander all over the work bench because of the vibration. To hold it in place, I glued a layer of 1" grey open-cell foam to the bottom. The foam flexes enough to absorb the vibration before it can move the sander.
Sandpaper disks to fit the disk were cut from an 8½"x11" sheet of sandpaper using a box cutter, and glued to the disk with rubber cement. Rubber cement will allow the sandpaper to be pulled off when it's worn, whereas a stronger glue would not.
I haven't done this yet, but I plan on reversing the disk and truing the back with a chisel too. This should not only help reduce the vibration by better balancing the disk, but also provide a second surface for another sandpaper disk of a different grit.
I will probably redesign and rebuild this sander someday. I would prefer an 8" sander without the protruding arbor.
© 2003 W. E. Johns