Hole Diameters

[geraldmorrissey]

I'm getting ready to install the strut attach bars on the main spar. It will require several 3/16' holes and one 1/4" hole. I miked several AN-3 bolts and found them to be between .1879 and .1882. Both too large for a 3/16" drill. I did not measure 1/4" bolts. A #10 hole which is an industry standard is .1935 or about .005 clearance or so. I have other options, I live in Seattle and have enormous resources. I can get a cutter ground to any diameter. A #11 is closer with about .003 or so. Is anybody reaming these holes? Just wondering what size others are drilling these holes too. The factory strut bars are drilled with clearance but I do not have the instruments to accurately determine the hole diameter. If the 1/4" bolts are oversize then it looks like a letter F drill is the only choice. Surely this has come up before.
Cheers
Gerry
Patrol #30 Wings

[dedgemon]

gerald, typically people use a #12 drill for 3/16 bolt holes (its 0.189), but I find that often a hole with a 3/16 bit will fit just fine if perhaps a bit tight. They tend to drill out a little bit larger than the shank diameter due to wobble of the hand drill.

[JohnS]

Isn't this what reamers are for.......finishing the bore accurately.

[alaskabearhawk]

I've always used a chucking piloted reamer for all my holes. Drill undersize and finish with the reamer...always a perfect hole (if you hold the drill straight). http://www.panamericantool.com/high-...g-reamers.html