I started a thread where I am going to build an edge sander from plans bought online. The plans call for a 3/4 HP electric motor at 3450 rpm but in the instructions they state that 3450 is too fast for sanding so they use a 4.5 inch pulley and 3 inch pulley to slow the speed to half. I am looking at motors online (I admit, this is not in my knowledge base) and found that there are 3/4 hp motors with 3450 rpm and then there are 1.5 hp at 1750 rpm.
I don't understand the relationship of HP to RPM. I also question, if the ultimate goal is to get the speed of the sander (belt moving across the wood presented) is considered best at 1750 RPM, why not use a motor rated at this speed and do away with the pulleys and belt.
I hope this makes sense. Any help is appreciated.