AN525 screws: suggested drill bit?

[SP1]

I'm about to put the AN525-10R screw hole through the longeron and aft fuselage skin (SNXB). Was wondering what others have used to drill the hole? Instructions say to get a nice tight fit. Thanks

[lgsievila]

Hi Sam,
AN 525-10R screws are 3/16" (.187). To get a tight fit you consider an undersize drill bit ,#13 and then use a 3/16" straight reamer. Not sure of the exact location you are talking about but if the screws are in shear, you don't want any slop at all in the hole.

[SP1]

Thanks Loren,
I'm glad I asked! Still trying to wrap my head around the nomenclature, and I the hardware kit hasn't come in yet.
This is for the holding the front fuselage to the rear fuselage via some hefty plates (F25 page, part F26-06). Hardware kit hasn't come in yet but I've got everything lined up.

[Rynoth]

Hi Sam,
AN 525-10R screws are 3/16" (.187). To get a tight fit you consider an undersize drill bit ,#13 and then use a 3/16" straight reamer. Not sure of the exact location you are talking about but if the screws are in shear, you don't want any slop at all in the hole.

This is what I did as well. Don't go straight to it with a 3/16" drill bit, it will probably end up oversized.

Same goes for AN4 bolts, use a "D" bit, not a 1/4" bit.

[sonex892.]

Back in the old days before reaming was the new norm. A good correctly sized drill was the recommended way..With thick material I found 9 times out of 10 ten a 3/16 bolt would still be too tight to go into a well drilled 3/16 hole without further clearing.
I'm not saying dont ream, just saying its not absolutely necessary.
The main thing either way is to get the hole perpendicular. I guess a reamer may help save the with a crooked hole.
Steve

[lgsievila]

Hi all,
Ryan-you are correct, any time you want a body fit bolt/screw you should drill undersize and then ream to the correct diameter. Sonex 892, I would be concerned about the 1 in ten times your drill action is oversize. When you use a reamer the attachment hardware acts as a dowel and that is what you want in a shear application-you don't want anything to move. That is also why you never use a threaded fastener in a shear application-reference Service Bulletin SNX-SB-008.
EAA Tech Councilor

[sonex892.]

Hi all,
Ryan-you are correct, any time you want a body fit bolt/screw you should drill undersize and then ream to the correct diameter. Sonex 892, I would be concerned about the 1 in ten times your drill action is oversize. When you use a reamer the attachment hardware acts as a dowel and that is what you want in a shear application-you don't want anything to move. That is also why you never use a threaded fastener in a shear application-reference Service Bulletin SNX-SB-008.
EAA Tech Councilor

All due respect Loren. I didn't say I had 1 loose hole in ten. I said 9 were too tight to insert the bolt without further clearing. If a sonex build is your first rodeo it is probably advisable to use a reamer.

[Bryan Cotton]

For critical wing and tail attach bolts I definitely drill undersize and ream to a tight fit. For the fuselage gussets I just did many steps in drill size and finished at nominal for a snug fit and a round hole. I always drill in many steps for bolt holes, otherwise they end up triangular.

[SP1]

Thank you all for your thoughts. I'm hearing that I should drill with an 11/64, then finish off wiht a reamer.