Drill bit size for a #10 screw

[aarvig]

I am at the point of dimpling and countersinking the Rudder counterbalance rib and lead weight. I borrowed a #10 dimple die from a friend but all I have is a #12 drill bit and #12 countersink. Is it acceptable to drill with a #12 for a #10 screw, then dimple the rib for a #10 and countersink the #12 hole with a #12 countersink?

[Walt]

#10 screw = 3/16" = .1875
#12 bit = .1890

For your particular application you should be fine. I like to use proseal when installing CB weights, helps fill the voids and makes the attachment bulletproof.

[az_gila]

Originally Posted by Walt

#10 = 3/16" = .1875
#12 = .1890

For your particular application you should be fine. I like to use proseal when installing CB weights, helps fill the voids and makes the attachment bulletproof.

No, an AN3 is not 3/16, it is 10-32 threaded, almost 3/16 but not quite.

The shank diameter of an AN3 bolt is 0.186 to 0.189 inches.

You #12 drill is just the correct size at the high end of the tolerance range....

added

Just for clarification, a #10 bit is 0.1935 inches, a pretty loose fit for an AN3 bolt.

[Phil]

Earlier on I was using the 3/16" bit for #10 holes but was experiencing cracks quite often. I think the stretching required for a dimple that large was the culprit.

So I moved up to a #12 bit (reamer actually) and the slightly larger hole kept the aluminum from having to stretch so much while shaping the dimple. I haven't had a single crack since moving to the #12 bits.

Phil