Drill bits to drill main spar attach holes.

[Sonex1243]

So for those of you who have drilled out the attach blocks with 3/8 bit and used AN6 bolt or trailer hitch pin – have you been happy with the fit? I’ve heard comments about having to lightly “tap” the bolt or pin into place after drilling.

I used the Fastenal bit I linked to earlier in this thread (sounds like the same one you are using). Unfortunately, I don't remember the diameter I measured for the AN6 bolt. My experience was the same as Corby202--only had to tap the bolts in when installing on the airplane.

I occasionally shake the airplane by the wingtip to see if there's any looseness and I haven't noticed any.

Chris,

Do you still have the Fastenal bit and would you be willing to loan it out? At the rigging stage now and getting everything set up for drilling. Thanks.

[Zack]

I used standard drill bits and reamers create the 3/8" holes in the spars before mounting them to the fuselage and ovaled the holes this way. This is how I corrected the ovaled holes. On the B model the final size is 0.5000, and I determined I needed a little more that that to clean up the holes, so I selected 0.5625 as the new target. I updrilled the fuselage attach points to 0.5000". Then I created guides made on a lathe from 0.5000" steel tubing to updrill the spar first 3/8", then 7/16". This got me a true hole of 7/16". I then used piloting reamers through the entire stack until I reached the 0.5625" final size. The tooling expense was high, but I saved the spars. The hardest part was sourcing an upsized bolt, this is what I used:

https://military-fasteners.com/bolts/sh ... nas6209-64

If I were to do it again, I'd use double margin drill bits to a smaller than final size, then work to final size with piloting reamers. I always drill undersize and finish ream, but a standard reamer can cut sideways if you don't have a solid jig/fixture. I purchased my piloting reamers from Pan American Tool.

[yx0020]

Hello.

I am getting ready to attach the wings and trying to see what my options are if attach holes get messed up. Unfortunately, the wings are already assembled so the drill guide method is not an option.

I bought this drill bit https://www.yardstore.com/drilling-and-cutting/aircraft-sheet-metal-drill-bits/double-margin-with-pilot/cobalt-double-margin-jobber-3-8-x-1-4-pilot-usa and after testing it on a scrap piece of aluminum, found out like a few other people on this thread that the resulting hole is a bit too large. If I still go ahead with drilling and the play while lifting wing tips is very noticeable, will turning AN7 bolt down to 0.375 or slightly larger be an option? Will it even be possible to do in an average machine shop and would it possibly change metal properties of the bolt aside from removing the coating?

The reason I am entertaining this idea is due to other poster's concern about sheer strength of other potential substitutes for the bolt.

Any suggestions on making perfect holes will be appreciated.

[Bryan Cotton]

Can you get a buddy with a lathe to turn down the drill? Would probably need to grind it down a little.

[yx0020]

Can you get a buddy with a lathe to turn down the drill? Would probably need to grind it down a little.

I do not have a buddy like that but I can try holding a sanding block against the side of a bit rotating in a drill press...

[Area 51%]

Have you considered an under-sized drill bit then using a reamer to get the fit you need?

Worked for me.

[yx0020]

Have you considered an under-sized drill bit then using a reamer to get the fit you need?

It sounds like pretty much everybody recommends using piloted drill bit while drilling assembled wings. I do not think I will be able to find an under-sized bit like that.

[Bryan Cotton]

Can you get a buddy with a lathe to turn down the drill? Would probably need to grind it down a little.

I do not have a buddy like that but I can try holding a sanding block against the side of a bit rotating in a drill press...

That seems like a stretch. I drilled my spars up to size on a drill press, then built the wings. Any chance you can set up your wings on the drill press? That would allow the last pass with the right size reamer and then use my drill bushings to rig to the fuselage.

[Area 51%]

Have you considered an under-sized drill bit then using a reamer to get the fit you need?

It sounds like pretty much everybody recommends using piloted drill bit while drilling assembled wings. I do not think I will be able to find an under-sized bit like that.

Of course you can........it's called a 23/64" bit. Then ream it up from there.