A simple item, but I don't see it mentioned here so...
I find that a D.C. motor speed control is one of the tools I will never be without, now that I have owned one. I was given a very good one by our tool crib attendant because it had amphenol plugs that were damaged in shipping, and he had recieved another on warrantee. I changed out the amphenol plugs for long pigtails with standard 15 amp male and female plugs and now use it most of the time I use a high speed D.C. tool on the boat. For the router, reducing the speed by about 15% reduces the distance the chips are spread by about 70%, and reduces the cutter speed to something more practical for cutting fiberglass. For the 5 inch grinder with the soft pad and sanding disc when used to prep small areas for glass work, set it at about 50 - 60% of max. It makes a 5 inch grinder into a tool that can be used quite delicately. For the electric 1/4 inch die grinder and a carbide cutter you can reduce the speed and be much more gentle, even using a ball cutter to clean up fillets without gouging. I have a powerfull polisher but it only has 2 speeds, and niether is right. With the speed control it can be perfect.
Word of advice though, when using reduced speeds, always reduce the cutting force or pressure accordingly. The tool will have less torque (which is what you are trying to achieve) but also less cooling air passing the windings in the motor, and when the voltage goes down, the current must go up if the resistance remains the same, since no one has found a way to defeat Mr. Ohms law. If the current goes up, so does the heat in the windings. Use it to "soften" the tools slightly, and use them with feel and you will not overheat anything, but if you are into hard cutting than go the other way and use a heavier extention cord and put the speed control back on the shelf. It will only work on AC/DC motors, ie. motors with brushes and commutator, it will not work on induction motors, or resistance loads.
Feetup