Originally Posted by Ed Cregger
I haven't found many sheet metal screws that are worth bothering with when using an epoxy engine mount. Goldberg had some (rounded shiny head) that worked perfectly for a while.
What I have discovered is that if you use the appropriately sized (small) body drill, you can drill through the epoxy glass engine mount and then tap the mount with threads for an appropriately sized machine screw (6-32 on the smaller sized engines). I have been doing this since the seventies and I have yet to have a mount strip its threads or for a bolt to come loose once properly tightened. Yes, I was skeptical when I first heard of it too, but you can't argue with positive/no failure results. I have built and flown many, many models since the late sixties and seventies.
If your threads are stripping out in your epoxy glass mount, your body drill is too large. Unfortunately, I don't remember the number of the body drill for 6-32 thread cutting.
After you drill the appropriately sized through hole, are you using a tap to thread the hole, or are you able to cut the threads just by screwing in the machine screw itself.