ETLB Squawk Forums — Archive

I never have a problem with drilling holes and reaming except when dealing with AN3 bolts or directions indicating to drill a 3/16" hole. For AN3, it seems I need a #11 drill bit. I'm wondering if I should just use #11 anywhere I see a AN3 bolt. Maybe my bolts or drill bit are defective?

John

I've been using a 3/16" bit for the AN3 bolts.  It works but it is a very tight fit.

Yes, and what happens with me is the cadmium rubs off it's so tight. Every other size is a nice snug fit, but AN3 whether metal or wood really won't fit in the 3/16" hole I drill, even if it's undersize and then reamed. #11 gives a fit just like other sizes. I think I'll use 3/16" first and if it's not working, I'll run #11 through.

John

There was a lengthy discussion of this subject on homebuiltairplanes this week.  Here's the link:  https://www.homebuiltairplanes.com/forums/threads/an3-bolt-with-3-16-or-11-bit.41198/

Thanks! That was me. The discussion left my head spinning. I think I'll continue using #11 bit.

I used a 3/16 bit for drilling AN-3 bolt holes.
With this, the bolt used to be bit of a tight fit, so
I had to ream the hole very gently to make it
a snug fit. Used a chain saw sharpening file
for reaming the hole. This file was long enough
and of perfect size for reaming the 3/16 hole.

For AN-4 bolts I think I used a 1/4 bit.

Thanks Ace. I'm probably a bit over the top. For metal, I like a nice tight round hole, not the triangle shape a drill bit gives. So, I typically use a D bit for AN4 then ream. There's also the fact AN bolts are a bit undersized on purpose. My AN3's are .1870 for example, not .1875 (so still can't figure out why they are so tight). Long story short, I'm drilling with undersized bits and now reaming to a size that more closely matches my bolts, not automatically using .250 or .1875 reamers. For AN4, I just ordered a .2480 which is closer to what I have. Oh, I saw at McMaster-Carr, they have a special "Precise" 3/16" bit in addition to regular 3/16". I picked up two of those also (3021A26 Drill Bit for Precise Holes, 3/16" Size).

Thanks!

John