Reducing the diameter of dowel on a table saw is easy to do on wood as well as plastic pipes. The most important step is to clamp down your sledge or mitre fence the desired distance, so you are not likely to slip. I would also only shave less than 2mm off the dowel at any one time. Table saw blades are not designed to take sideward pressure, so if you want to keep your blade square don’t over work it.