New (Second) Builder Questions - Inspection

[BobDz]

Here are a few tips for drilling high strength materials like stainless steel.

A "standard" drill bit is 118 degrees.
Resharpen the bit to 135 degrees.

Cobalt drills work much better on stainless steel than high speed steel bits.

Sharpen a cobalt bit to 135 degrees and you have the best of both worlds.

I haven't thrown away a drill bit in many years.

[sonex892.]

While the normal way to drill stainless steel is, more feed, less speed, always using sharp bits and cutting fluid. When drilling these damned stainless rivets there is still a need to follow this rule, but just a bit less feed. If I tried to drill out a stainless rivet with as much force as I use when drilling stainless material, the rivet will spin nearly every time.

Years ago a friend rebuilt his sonex after he'd flipped it on its back during a forced landing. To dismantle he used larger diameter bits, 5/32 or 3/16. The smaller #30 bits tended to grab and spin the rivet as soon as the outer edge of the drill enters, whereas the larger diameter bits would cut the rivet head off before the outer cutting edge entered the hole. With the head off the drill bit automatically stops cutting. Then just knock the rivet tail out with a pin punch.

I use his method myself. While it isnt 100% successful in stopping absolutely every rivet spinning, I have a much higher success rate. Also tiny pair of vise grips to grab whatever rivet tails you can before drilling helps.

[BobDz]

For what it's worth...

I recently found 135 degree cobalt bits at Fastenere.
I too use a 5/32" bit to drill out 1/8" rivets.
Restocked my drill bits, free shipping.