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Originally Posted by Viking
One of the successful drum sanders I've seen runs at around 1000 RPMS.
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RPM=Revolutions per Minute. It is plural. No need to pluralize a plural. RPMS (RPM's, RPMs, etc.) is incorrect. Semantics, I know.
What is more important than drum speed is surface speed in feet per minute. That is, how many feet of sanding surface pass a given point in a given time. That varies with drum diameter and rotational speed (RPM). For the same rotational speed, a larger drum will have a higher surface speed than a smaller drum.
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A dimmer switch could bring that level down to a more reasonable (and safe, I don't want the drum to fly apart) speed...
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If the motor is air cooled, reducing the speed of the motor will reduce the speed of the cooling fan. You run the risk of frying the motor. A better solution is probably to use a more appropriate pulley ratio, one that gives you the speed you want.
You'll need a means of securing the drum to its shaft so that the drum doesn't spin on the shaft. The drum will need to be concentric on the shaft for a) accuracy/repeatability and b) for dynamic balance of the rotating mass (drum). You'll need a means of attaching the sandpaper to the drum.
I'm guessing from the photo that your finished drum will be about 5" or so in diameter and 20" or so long. The combination of drum diameter and shaft diameter needs to be sufficiently stiff to prevent flexing mid-span under load.
Ideally, you'll want about 400 CFM of air flow for dust collection. You'll also want some sort of dust shroud to keep the dust "in". Alternatively, use it outside.
Grit Laskin wrote an article about his home-made drum sander in an early issue of Fine Woodworking. The article provides fairly complete working drawings. You might want to read what he did. Or not. Another author gave full plans for a home-made wide-belt sander in a different issue of the magazine.
I literally jumped for joy the day I disassembled my home-made sander in favour of a commercially made one with a variable speed feed and drum speed, quick-change sandpaper, accurate depth gauge... Back in the day, sanders started at over $20k: now one can be had for as little as $600.