The workpiece emerges down the white ramp.
The adjusting crank is a casement-window replacement from the hardware store; the axle is a piece of 1/4
inch allthread, and spacing and tension is maintained with a stack of regular and coupling nuts and lockwashers jammed (locked) together.
There is a brass threaded insert in the ramped table.
The dial indicaror is bolted to the aluminum plate that serves as the adjusting handle bracket.
By now you've wondered about the motor. It's from a B&D electric lawnmower, it's a universal (brush)
motor and it's speed is controlled by the light dimmer in the conduit box. This thing is a very high speed motor similar
to a router, which is why the speed is reduced by the belt drive. Do not use one of these motors without this reduction as
the centrifugal force can fling the off the sandpaper no matter how well glued on.
The drive belt is a Browning 1/5" pitch synchronous drive gearbelt, and of course the pulleys match; there's
a 15 tooth on the 5/16" motor shaft and a 48 tooth on the 1/2" drum shaft. These items were found in the Grainger catalog,
along with the drum shaft bearings which are self-aligning ball bearings in inexpensive pressed steel housings.
The worktable is a stack of mdf wedges cut to 30-60-90 triangles and glued together. Seal
these with shellac or similar, so they won't change shape and size with humidity, and cap with formica for a wear surface.
When this table is adjusted toward the sanding drum by 0.002" according to the dial indicator, the gap changes
by only 0.001", due to the angle of the ramp. If the ramp were 45 degrees, the gap would close by 0.002".
Here is the sander with the table removed.The pillow block risers are set into shallow dadoes, which help
to keep the drum axis and the ramp square with each other.
Bearing removed from shaft to show stacked plywood assembly.
The shaft was cross-drilled so a pin (a nail, actually) could be buried in the ply glueup. A temporary
tool rest allowed the drum to be turned as if on a lathe, and the drum received a final truing with a sandpaper covered board
slid between it and the ramp.
All-birch plywood, strong, stiff, and relatively stable, is a good choice for this sort of construction.
A piece of Bolivian rosewood starts down the ramp against the drum's rotation.
Reach under with the other hand and continue to feed by pulling smoothly.
