Paul - Ditto on the safety aspects. After all your work, it would be a shame if you blew a bit due to vibration and possibly injured yourself. A shattered bit at 20k rpm could send pieces flying like bullets. Another consideration is, high speed steel bits are hard, and your file would likely wear out before you accomplished your goal. Just some advice - you are about to invest a significant amount of time and $ in a boat project. Why not invest another $20 or so and buy a set of real carbide bead and cove cutters? Their cost is negligible compared to the total cost involved, and they would last for several boats. There are enough variables in setting up and using them - don't look for trouble in trying to make do and save a buck. Eliminate as many variables as possible in your project, and reap the satisfaction of a job well done, and done safely.