Drilling Fiberglass is Tricky Business
by Dick Zakrzewski
Drilling holes in fiberglass bodies and accessories can be very tricky business. If not done properly, you can chip off significant pieces of gel-coated surface. The bigger the drill bit, the greater the risk of chipping. This is particularly troublesome if you're drilling a hole in a finished body and the surface isn't covered afterwards! If you're like me, you don't like the chipping even if the surface is going to be covered.
Trying to cut through gel-coat with the shallow rake angle of a drill bit is what actually causes the chipping. The cutting edge quickly digs through the layer of gel-coat then lifts up. The obvious solution is to keep the drill's cutting edge away from the gel-coat. The following procedure will accomplish this objective.
- Step 1
- Make a small indent in the surface where the hole is to be made. Use a very sharp scribe or ice pick. This will prevent the drill from wandering and damaging surrounding surfaces.
- Step 2
- Drill a small pilot hole about 1/8 inch diameter. Maintain a relatively slow drill speed and advance the drill bit very slowly. Let the drill bit do all the work.
- Step 3
- Chamfer the pilot hole with about a 1/16 chamfer. See Photo
- Step 4
- Drill the hole again with a slightly larger drill making sure
the second drill is inside the diameter of the chamfer.
Again maintain a relatively slow drill speed and
let the drill bit do the work. See sketch #1.
- Step 5
- Repeat the steps 3 and 4 until the desired hole size is
achieved. See Photo #2.
I realize that this may seem like a lot of work just to drill a simple hole, but the results are definitely worth it - a perfect hole with no damage. See photo #3.