Bit for Drilling Fiberglass

[Steve Carpman11081]

We would like to add another vent for our holding tank. This will require drilling a 1" hole in the hull. What type of drill bit should I use to minimize damage to the fiberglass? For example, will a 1" plumber's bit work?

 

[Frank Walker]

Above the Water LIne

A small hole saw would probably be your best bet. One device that I have found handy is a small rasp that fits in a 1/4" drill. If you can get a 3/4" hole in the hull then the rasp will enlarge it to 1 to 1/1/2" quite easily.

 

[Kevin13713]

I'm no fiberglass expert but...

I have done this myself with good result and I can tell you what I used...a 1" cup saw drill bit that I bought at Sears. It mounts on something that looks like a conventional bit that drills a pilot hole before the cup bit hits the fiberglass. Before I drilled I covered the fiberglass area with a good masking tape to prevent as much cracking or splintering as I could. I drilled it slowly and once the pilot bit came through the other side I drilled from the other side just a bit and to the point where the cup bit evenly cut the inside fiberglass (also taped). I did this to prevent splinterintg the fiberglass on the inside when the drill bit came completely through the new hole. Then I finished drilling the hole from my starting position. It worked great for me...no cracking, splintering...just a nice clean hole. Best of luck.

 

[Hal]

Use a bit that cuts the edges first!

I work on aviation composite parts frequently and the best way to drill is to use a bit that cuts the edge with a cutter slightly before it cuts the main part of the hole... Any woodworker would recognize this as a Forstner bit. They cut a very clean round hole and are available in 1/8" sizes to over 2". Since they cut/slice the fibers before they cut the main body of the hole you will get a very clean cut. Make sure you seal the fibers exposed in the hole after drilling with resin or epoxy. This will prevent water from wicking into the hull over time if it ever leaks. (This is a good idea anytime you cut and expose the glass fibers when working with composites)Forstner bits drill an almost flat bottomed hole so they also work well for drilling plug holes or drilling out teak plugs. I bought my set at the local Home Depot. 1/4" to 2 1/4"in 1/8" increments for $50. Good luck!