[Jack21]

Which is why I like a tool operating speed of between 8,000 - 16,000 RPM, not 26,000 RPM. If it the hot steel chips pit glass, imagine what they'd do to your arm.

Safety glasses are a must. If you're getting into head porting on iron heads, a respirator is a god idea too. Respirator not necessary for little clearancing jobs. A shop vac usually gets the chips off the floor and workbench.

Air die grinders are reasonably inexpensive, but the carbide files you need are not carried by Sears, Home Depot, or True Value. Found most recent vendor by doing a search on Tools & Abrasives. Summit also sells a few of these. Look in the engine section under porting tools.