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prkaye

Well Known Member
What drill bit do I use to drill a hole for an AN509 screw?

Can suitable drill bits be bought at a hardware store, or do they also need to be of "aircraft quality" ?
 
What does the Standard Aircraft Handbook say?

I'd look it up in the Standard Aircraft Handbook. If the correct drill size for that screw is one of the very few that you can get a hardware store, buy it. If it's a "Number" or "letter" size, then you'll probably have to get it at a specialty store.

Not necessarily an aircraft tool supply store, mind you...a place that sells to machinists and machine shops will do.
 
Not sure if I have that handbook...been looking in the circular but can't seem to find the information there...
 
prkaye said:
What drill bit do I use to drill a hole for an AN509 screw?

Can suitable drill bits be bought at a hardware store, or do they also need to be of "aircraft quality" ?
Click to expand...
The easiest way to determine what drill bit to use in any situation is to measure the fastener diameter with a micrometer and then refer that measurement to a drill index chart for the proper drill bit.

Yes, common hardware store quality drill bits are satisfactory but like anything else, you get what you pay for. Generally speaking "high speed" drill bits wear out the quickest.
 
AN509 screws come in several different diameters. You need the full part number to know the diameter, or you can simply measure it, as others suggested. If the part number ends in something like 8R10, the 8 means it is a #8 diameter, and the 10 means it is 10/16 long.

#6 diameter needs a #28 drill, generally speaking.
#8 diameter needs a #19 drill, generally speaking.
#10 diameter (same as AN3 bolt) needs a #10 drill, generally speaking.

Note - the above drill sizes leave a bit of clearance between the screw and the hole, which is what you want in most cases to ease assembly. But, there are a few special cases where you might want a smaller hole to get a tighter fit with less slop - e.g. flight control system related holes.
 
so AN509-10R16 takes a #10 drill bit? A number 10 drill bit is larger than a #12 drill bit, correct? Seems strange because the #12 drill bit is a bit bigger than the pre-drilled holes in the counterweight (this is the bolt that holds the rudder counterweight to the top rib). So a #10 would be larger still...
 
Useful tables:

Nominal screw sizes
Nominal drill sizes

A 10-32 screw has a nominal thread diameter of 0.190". A #12 drill has a diameter of 0.189". If you use a high speed drill, the hole will end up a bit larger than the nominal drill size, so a #12 drill might work. But it won't leave much room for any primer. A # 11 drill is 0.191", and a #10 is 0.1935".

Phil - Valley Hardware at 65 Bentley Ave. is a good local source for number sized drill bits.
 
#6 diameter needs a #28 drill, generally speaking.
#8 diameter needs a #19 drill, generally speaking.
#10 diameter (same as AN3 bolt) needs a #10 drill, generally speaking.
Click to expand...

Ken Scott from Vans said in an email "it's a #10 screw --
3/16" diameter -- so a #19 drill (or a 3/16" if you don't have number
drills that big)". That doesn't jive with the table you posted the link to, Kevin. Is it possible Ken has made a mistake here??

I find this very confusing... so for a #10 screw you need a #19 drill??? Why don't they number things consistently so that for a #10 screw you use a #10 drill bit?? Or maybe for a bit of extra space a #11 or #12 (which would be slgihtly bigger than #10)... but #19??

Does anyone else also find it inconsistent and irrating that AN4 rivets use a #30 drill, and AN3 rivets use a #40 drill (seems backwards... why not number things so that AN3 uses #30 and AN4 uses #40 ??)
 
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