Z-bracket hole thread damage & cuttings

[spaceflightmeow]

After tightening the bolts on the right wing Z-brackets for the first time, I noticed some cuttings and residue on the bolt.

http://imgur.com/a/aUbmS

EDIT: airguy, good eye. The nutplate at the bottom of the image did have a bucking bar hit it on the threaded part.

After removing the bolt and cleaning it, a bunch of black gunk came off. Some of this is material from the nutplate.


Looking at the hole in the Z-bracket and spar web, it appears that the bolt threads have cut threads in the spar web (and also a little bit in the Z-bracket)


How bad is this? Can I repair it by reaming the holes smooth?

[wirejock]

I'll take a stab. Maybe an expert will comment as well.

I would drill out the nut plate rivets and remove it then ream the hole to clean it up.
Reinstall a new one with a bolt in the nutplate so it stays centered.
That's the part I would be concerned about. Why is the nutplate not centered on the hole and will the z-bracket align when the nutplate is correctly aligned in the hole.

[airguy]

Common problem, the hole in the nutplate was not accurately aligned with the hole in the workpiece, it happens. On non-critical fasteners locations you could drill the screw hole a size or two larger to help with any misalignment before riveting the nutplate, but they really should be accurately aligned. If you are using clecos with bent pins, this is a frequent result.

Drill out the nutplate, cleco a new one in place with a NEW bolt in it to center it, rivet, move on.

Throw away the old nutplate and bolt.

[BillL]

Originally Posted by airguy

Common problem, the hole in the nutplate was not accurately aligned with the hole in the workpiece, it happens. On non-critical fasteners locations you could drill the screw hole a size or two larger to help with any misalignment before riveting the nutplate, but they really should be accurately aligned. If you are using clecos with bent pins, this is a frequent result.

Drill out the nutplate, cleco a new one in place with a NEW bolt in it to center it, rivet, move on.

Throw away the old nutplate and bolt.

I hate when that happens, and without changing technique, it will happen a lot.

I have a worn nut plate and use a counter sunk screw in it to ensure it is centered, then drill the wings.

[spaceflightmeow]

OK, I will install a bolt in the nutplate before riveting it. Makes sense.

On the Z brackets, I bolted on a sacrificial nutplate to match drill the rivet holes. So at that point the rivet holes were nicely centered. It looked like this:


I did not have a bolt installed in the nutplate during riveting, I just clecoed one side. Maybe the nutplate got out of alignment during riveting.

[spaceflightmeow]

I should note, also, that a virgin nutplate and bolt lubed with Boelube paste #70307-12 still produces quite a few shavings:



EDIT: When I say "virgin", I mean the bolt threads are virgin. The rivet holes obviously have wear and tear from handling with pliers, etc, so don't look at that.
The shavings in the foreground on the wood came from the bolt or nutplate.

That's just an aside. Obviously, the big swirly cutting in my first photo is evidence that the bolt has cut a thread into the spar.

[airguy]

Another key to this puzzle is shown in your photo - the edge of the nutplate is damaged from compression on the end, where your pneumatic squeezer (or the bucking bar) contacted the nutplate first and then jumped off the nutplate and onto the rivet, when you were riveting the nutplate in place. I've done this myself too many times, and seen this result, it can easily make the nutplate unusable. In your case that damaged area is almost certainly what caused the thread damage on the bolt that is seen as well as the curlique of metal shaving, and the holes are also slightly misaligned which resulted in the bolt threads contacting the spar.

[RVDan]

I might also suggest that you buy a nutplate jig for the appropriate nutplates. They really make drilling the nutplate holes easier and keep things aligned.

[spaceflightmeow]

OK, will consider getting the nutplate jig.

One question about the re-installing new nutplates: If I were to bolt on a fresh nutplate and re-use the original rivet holes, but they don't line up with the nutplate, is it acceptable to slightly elongate the rivet holes rather than rotating the nutplate and making a fresh set of rivet holes?

Seems to me, it's OK, since the rivets are just holding the nutplate on. It seems better to do that than make a new set of holes.

[airguy]

I would prefer to see the nutplate rotated 90 degrees with fresh holes rather than elongating existing rivet holes, but that's a personal preference. The only purpose of the rivets here is to stop the nutplate from rotating, there is no real stress requirement on the rivets beyond that.