I can't use a 1/4" bit with my Dremel, so here's a quick and dirty method which works. Find a nail that will fit in your Dremel chuck and cut off the head. Or use a drill bit as shown below. Cut a strip of sandpaper about 3 to 4 inches long and 1 to 1 1/4 inches wide. Duct tape the strip to the bit. Wrap the strip around the bit counterclockwise, covering the tip of the bit. (Dremel turns clockwise). This works for cylinders and is especially good for exhaust ports. Remember to keep the bit just off the surface you are working on, letting the flapping of the strip do the work. When used this way, it will not harm the surfaces. As you work, the end of the strip will shred. Cut off the shredded part and continue. To get the small radiused corners of the exhaust ports, find an appropriate size bit and wrap sandpaper around it, then use it to sand manually (use fine sandpaper when sanding manually). When using the flapping technique you can start as coarse as 150 grit and work up to 400+.
