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Z-bracket hole thread damage & cuttings

spaceflightmeow

spaceflightmeow

Active Member
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
XXTvFGX.jpg

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.
phh1831.jpg


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)
WY952N0.jpg


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

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.
 
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.
 
airguy said:
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.
Click to expand...

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.
 
Nutplate alignment with bolt

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:
8MksOZu.png


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.
 
Some of the shavings are from the bolt, nutplate

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

pYYiylu.jpg


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.
 
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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.
 
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.
 
Re-use old nutplate rivet holes with fresh nutplate?

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.
 
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.
 
airguy said:
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.
Click to expand...

You're right, there's no stress requirement on those rivets - that's why I ask if it's OK to elongate the holes. Doing so eliminates adding two fresh holes to the Z-brackets.

I suppose I could also put rivets in the old holes..
 
spaceflightmeow said:
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:
8MksOZu.png


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.
Click to expand...

You are using logic to defend the method that allowed this plate to be misaligned. This method still does not center the nut plate to the hole. That is what the countersunk screw will overcome. I tried this too, but there is enough variation you still get your off center result too often. I don't think all the nut plates are in line, and there is enough variation in hole sizes that the nut plate drill guide tool requires a specific hole size. Doing just a few is ok with the screw, but a drill guide is definitely the way to go if doing more than 5 or so nut plates.

On plates that are out of line (despite my best efforts), I have a stock of floating plates on hand and just install one of those quickly and move on. No more drilling, just too much additional aggravation, just remove rivets and install a floater in the same holes. Besides, the parent material will carry the shear loads.
 
Floating nutplate option

I really appreciate the continued advice. Let me try to understand a couple more things.

The Z bracket holes were reamed to #12 (0.189") to accept the AN3 bolts. The #10 size nutplate jig I found here has a 0.191" pilot. So I would have to drill/ream to #11 to use the nutplate. Is that too loose for the AN3 bolt? I need to ream out to remove the thread cut pattern anyway (or just remake them....sigh).

EDIT: Answered my own question while waiting. #10 seems way too loose for an AN3. So I can't use that nutplate jig. I can't even find one that exists for this size fastener.

I'm tempted to go the floating nutplate route here. Is F5000-3 or MS21059L3 the correct drop in replacement to K1000-3?
 
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spaceflightmeow said:
I really appreciate the continued advice. Let me try to understand a couple more things.

The Z bracket holes were reamed to #12 (0.189") to accept the AN3 bolts. The #10 size nutplate jig I found here has a 0.191" pilot. So I would have to drill/ream to #11 to use the nutplate. Is that too loose for the AN3 bolt? I need to ream out to remove the thread cut pattern anyway (or just remake them....sigh).

EDIT: Answered my own question while waiting. #10 seems way too loose for an AN3. So I can't use that nutplate jig. I can't even find one that exists for this size fastener.

I'm tempted to go the floating nutplate route here. Is F5000-3 or MS21059L3 the correct drop in replacement to K1000-3?
Click to expand...

Hi Dmitry,

Don't over think this. Get a #12 pilot nut plate jig to drill the rivet holes. While you're at it, get a full set for AN6, and AN8 screws as well. Use the jig for the rivet holes, then install a fastener into the nut plate, plus a cleco on the first side for riveting. Also, I use a bee's wax toilet gasket to dip the screws into before installing into a nut plate for the first time. This helps the faster thread in without galling...especially useful for #6 and #8 fasteners.

No need for floating nut plates. They are heavier and much more expensive!

Skylor
 
spaceflightmeow said:
I really appreciate the continued advice. Let me try to understand a couple more things.<snip>

I'm tempted to go the floating nutplate route here. Is F5000-3 or MS21059L3 the correct drop in replacement to K1000-3?
Click to expand...

10 floating nut plates of various sizes is way cheaper than a handful of nut plate drill guides! They also work where a part has multiple nut plates with tight holes in the mating parts and one is too tight to get the screw started straight. Like floor pans, and other such parts.

As to over thinking - you got the picture now about the guide pin diameters.

As to the nut plate number, that looks like the correct floater for this instance (MS21059-LX) - 1" spacing for the rivet pattern. I always look to General Aviation Hardware tech information for this. They have excellent reference materials.
 
Nutplates

BillL said:
10 floating nut plates of various sizes is way cheaper than a handful of nut plate drill guides! They also work where a part has multiple nut plates with tight holes in the mating parts and one is too tight to get the screw started straight. Like floor pans, and other such parts.

As to over thinking - you got the picture now about the guide pin diameters.

As to the nut plate number, that looks like the correct floater for this instance (MS21059-LX) - 1" spacing for the rivet pattern. I always look to General Aviation Hardware tech information for this. They have excellent reference materials.
Click to expand...

There are a total of 42 nut plates for the Z brackets. At $0.60 a piece (pretty cheap, actually) that's approximately $30 to buy 50. But you still need to drill the rivet holes...

Brown tool sells the nut plate jigs for $29.95 each....

And the weight difference may seem negligible, but it all adds up!

Skylor
 
Oops - we need alignment

skylor said:
There are a total of 42 nut plates for the Z brackets. At $0.60 a piece (pretty cheap, actually) that's approximately $30 to buy 50. But you still need to drill the rivet holes...

Brown tool sells the nut plate jigs for $29.95 each....

And the weight difference may seem negligible, but it all adds up!

Skylor
Click to expand...

I am sorry - we are not on the same page :eek:. You are absolutely correct ( I agree . . ) for moving forward on a new task. I am talking about the "production defects" like the OP. Just use the floater as a repair procedure. No problematic realignment, or new set of nut plate rivet holes. Just remove and replace with the floater and move on. NOT for all nut plates.
 
BillL said:
I am sorry - we are not on the same page :eek:. You are absolutely correct ( I agree . . ) for moving forward on a new task. I am talking about the "production defects" like the OP. Just use the floater as a repair procedure. No problematic realignment, or new set of nut plate rivet holes. Just remove and replace with the floater and move on. NOT for all nut plates.
Click to expand...

You're absolutely right Bill...

For limited usage the floaters are fine. I'm just advocating against the use of all floating nut plates in lieu of accurately drilled and attached non-floating nut plates.

Skylor
 
Over on this AN3 bolt discussion thread, there seems to be no concern about using a #11 hole for an AN3 bolt. It's a tension fastener, not a shear fastener, so the slop is acceptable.

This is good news, since that means I can ream to #11 to clean up the thread cut areas on the existing Z-brackets. I can even replace the nutplates with new non-floating ones, grab some fresh bolts, and it should all go together fine.

Also, a #11 hole will just accept the 0.191" pilot nutplate jig I linked earlier.
 
The thread marks on the z-bracket and spar web holes indicate that the hole on the z-bracket is slightly misaligned with the one in the spar web. This is very common when Vans' instructions are followed to the letter. The instructions say that it is acceptable to elongate the z-bracket holes as required to compensate.

A better solution, IMHO, is the alternative z-bracket location method, popularly known (and searchable ;)) in these forums as the Checkoway method. Jason Beaver details it nicely on his build log.
 
The Checkoway method helps you locate the baffle rivet holes on the Z-bracket flange, after the bolt holes are drilled on the other flange. I executed the steps the same way as Jason Beaver, by match drilling the bracket bolt holes using the spar as a guide. The problem is, the spar is thin so it's not much of a guide. The holes were drilled and reamed to #12 by hand (without a drill bushing).

I called Van's. They said it's OK to enlarge the holes up to #10 if needed, with the caveat that "they haven't done the analysis".

I can re-do the brackets and be more precise - use a drill block when match drilling, and bolt the nutplates down before riveting. That should help. I'm still not sure if it's necessary, given that these are not close tolerance bolts to begin with. The intent seems to be to use these as tension fasteners, not shear pins.
 
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