I needed to drill an 8-ft. long hole in the EPS core of a stress-skin panel in order to install a vent pipe for a kitchen sink. I don’t know of any off-the-shelf bits or hole saws that are designed for a task like this, so I made my own, using a piece of the same pipe that would end up in the hole. I used my coping saw to cut teeth in the end of a piece of ABS pipe. A coworker improved my design by using a Sureform plane to sharpen the teeth.
As shown in the drawing, I mounted the other end of the 2-in. pipe in a 2-5/8-in. dia. hole saw. It fit perfectly. Three drywall screws through the slots in the side of the hole saw secured the ABS. Presto! I had a hole saw 8 ft. long attached to my 1/2-in. Hole Hawg drill. It easily cut a hole in the foam that was the exact size I needed.
Jim Frandeen, Soquel, CA