Re: drilling into fiberglass
Fiberglass is remarkably strong and if any reasonable thickness at all, say 1/8 inch or more, will hold screws well. There are, however, several tricks to be used to get a quality job.
1. start with a smaller hole. then chamfer the hole with a countersink or a larger drill bit than the ultimate hole. Then drill the final sized hole and chamfer it. The reason for this is that Gelcote is brittle and tends to chip. The chamfer helps to prevent chipping.
2. If you are using self tapping or sheet metal screws, be sure to drill the hole to the proper size of the shank. It is natural to want a tight fit of the screw in the hole, but it is nearly impossible to force a self threading screw into an even slightly undersized hole---even in thin sections of fiberglass---to the point where you will damage thin sections. In thick sections it takes so much force that you will damage the screw slot and sometimes you can snap off the screw.
3. If you chamfer the final hole about 1/16 inch, then put a little RTV silicone seal around the screw, the seal will fill the chamfer and act like a gasket, keeping water from weeping down the screw and through the hole. Thread the screws into the holes before you mount the gimbal to cut the initial threads and it will be much easier to thread them the second time to mount the hardware.
Oh yes! it needs to be said: Please use stainless screws. Nothing looks as ratty as rusted fasteners on the dash. And measure twice and drill once---that way you should be able to mount hardware straight. Crooked fittings and hardware are a pet peeve of mine.
