My approaches
In experimenting to find the fastest tip I have made quite a few of them. I use #8 screws and a lot of them (just under 50 per tip) so my sizes are different. My airplane is a RV-6A so even my stock tips may be different than yours.
I was starting to describe my process which is very methodical to assure no gaps anywhere especially at the front end. Ah there I go again...
I dimpled the skin holes and initially countersunk the fiberglass with a proper size countersink tool. I counter sunk the rivet holes with the 3/32" countersink tool. The countersink tool cut the fiberglass cleanly with no problem in both instances. From what I'm told the fiberglass cutting dulls the cutter faster than metal cutting but it hasn't affected my work yet. If it does some day I will buy a new cutter.
On my first set of tips I was concerned about the strength of the platenut installations and I decided to back up the fiberglass with 0.016" aluminum.
As I developed my racing tips I had the "already drilled and dimpled wing skins" to deal with so the relatively precise match drilling process with clecoes in every hole had to be modified. The precision is still pretty good but it is not "slam dunk" simple. Through this effort I learned a few things for my application:
- A 3/8" hole in the fiberglass, after the platenut mounting holes are precisely located, works just fine for accepting the wing skin dimple - no countersinking required.
- No aluminum backing strip is required even though I change my tips from short range racing, to long range cruising configuration several times each year.
- Floating platenuts can be installed in place of the fixed dimpled platenuts and they will compensate for locations where a screw can be installed but it binds against the edge of the dimpled wing skin hole. The mounting hole spacing is the same and if you drill a rivet out and damage the fiberglass rivet hole you can install a local aluminum backing strip as part of the platenut installation.
Bob Axsom
