Actually, the crucial thing is the effective linear speed at the edge of the polishing mop, the value of which is dependant on the material being polished, and the polishing compound in use. A secondary consideration is the cooling of the mop. A large mop spends less time in contact with the work piece, so remains cooler during the polishing, which is less likely to damage the work. A look in the catalogues of the materials firms should show a suitable polishing compound for thermo plastics, and the will often come in different grades - cutting for rough work, and finishing for final buffing. A good UK supplier is Cetelem. My polishing set-up is made from an old double-ended, floor standing drum sander, fitted with "false noses" - the tapered screws that hold the mops (remeber you need a left hand and a right hand one for a double ended machine!). It is run from a single phase 1/3 HP motor, with a three step pulley to allow for speed changes (I ought to fit a varible speed drive, but haven't found a cheap one yet). The floor standing base makes the unit nice and stable. If you start polishing, make sure you have suitable protective clothing (goggles or face shield, leather apron, leather gauntlets, and dust mask), as the mops have a habit of picking up any item you are holding, and throwing it back at you! In the case of hard plastics (e.g. Bakelite), beware of stress fractures in the material - I've had a radio case shatter into razor sharp splinters - it took me hours to get them out of my arm (hence the protective clothing...........). Jim.