Nutplates and inspection panels

[Bradrock]

Nut plates have received some attention on this and other forums. I understand that k1100-06 are dimpled for flush screws such as on the inspection panels.

I see Eric used K1000 nutplates - what does one do about the dimples on the backside if using K1000's? (I have 500 of them!). Is it ok for the nutplates legs to sit on top of the dimples or do they have to be flush? It looks a little messy when riveted on top of the dimples but my understanding is that the nutplate merely needs to be held in place so that the screws will align.

Some direction here would be appreciated.

[Battson]

Short answer - you are good. I used the K1000 too, for the whole plane (dimpled or not), apart from a few one-armed nutplates here and there.

If you have a dimple die set for your rivet squeezer, and a countersinking reamer, then you are set. It was easy.

You can dimple the rivet holes of the nutplate, for flush riveted ones like the wing inspection ports and tanks, or you can put a straight K1000 over a dimpled set of holes. Both work out fine.
For the main threaded receptacle of the K1000, you can ream the opening a little to allow it to sit lower on a dimpled hole, per the Bearhawk Manuals. Just don't over do it, or you might weaken the nutplate. Again you can also ignore the dimple under the main receptacle and just use a straight nutplate. But that is a little untidier and probably slightly weaker, because the larger diameter dimple creates a larger stand-off. I would relieve the main receptacle to allow the nutplate to sit flush, in structural applications like the wing covers.

[Bradrock]

Great. Thanks Jono.

[jaredyates]

I had to grind a little off the female 3/32 die to clear the threaded section of the nutplate, but they dimple just fine.

[nichzimmerman]

How much material have folks removed when countersinking k1000-6 nutplates? I feel like I'm removing too much material to get the nutplates legs to sit down on their dimpled holes. In the photo, the small countersinking on nutplate A does not allow the legs to touch as shown in the second photo. The large countersink on B allows it but I removed nearly half the threads to get there. Thanks in advance.

- Nic

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[jaredyates]

If the screw hole was dimpled, I always used the countersink version of the nutplate (k1100 or MS21049). military-standard-ms21049-series-two-lug-low-height-100-176-countersunk-nutplate-4.jpg
If the screw hole was countersunk in the substrate, then I would use the k1000 as pictured.

[Archer39J]

I haven't countersunk any #6 nutplates, they just sit on top of the 3 dimples like in your photo.

I find getting them to sit down flush is a pain, so I cleco both rivet holes and put in a screw to hold everything tight in place, then rivet. Seems to work well that way.

[nichzimmerman]

It's a bit hard to see, but in the photo there is a gap between the legs of the nutplate and the top of the dimples. You're saying that's ok?

[Archer39J]

It's a bit hard to see, but in the photo there is a gap between the legs of the nutplate and the top of the dimples. You're saying that's ok?

Prior to riveting I see a tiny gap like you notice, after everything cinches up nicely save for one or two nutplates I may or may not replace. These only need to keep the nutplate from rotating really. If you get a good shop head I wouldn't worry if it's stood off a couple thou...

Take some scrap and do some test nutplates to see if it's acceptable to you, that's what I did.

[Ray Strickland]

FWIW: I have found it very helpful to run a 6-32 tap into each nutplate after installation...greatly reduces the number of sheared-off screws that have to be drilled out. Also, using anodized instead of stainless screws seems to help.

[jaredyates]

This might negate the locking capability if you tap too much, something to be aware of.

[Collin Campbell]

Ray, I run a tap into the nutplates as well. Of course a little common sense is helpful here...you don't want to take away too much of the locking feature. I just run the tap in about half way or so. This is a tip I learned a long time ago from the RV guys. It sure makes the screws easier to install and remove! And yes, I even use a lot of stainless steel screws...I know.. the galling thing. Put a tiny drop of fuel lube in each nutplate. "Different strokes" as they say...

[Archer39J]

With most sincere respect to Ray I quite strongly disagree about running a tap through a nutplate. Doing so eliminates the self-locking feature of the crimped body and, strictly speaking, destroys your standard mil-spec hardware (though countersinking effectively does this as well).

Installing, removing, and re-installing in excess of several hundred or so #6 screws now I've had exactly 1 head snap off and that was my cross threading to begin with. One thing I don't like about the spec'd MS screws is how mangled the phillips head gets, so my ACS cart has a couple hundred NAS514s in queue. I would recommend that before trying to alter standard hardware.

[davzLSA]

I hate Philip head screw for that reason, they are so easy to strip out especially with the locking nut plates. I am going to use socket headed stainless screws, they come in flush and pan head. So I can use a an allen bit to insert and remove the screws.

[jim.mclaughlin924]

I would like to use socket head, but are they available with the 100degree taper to match the dimple dies and countersinks?

[Ray Strickland]

Of course, one has to use some judgment in how far the tap is run in.

[Collin Campbell]

Speaking of the locking feature on the screws... On the plans, Bob recommends using #6 screws (also aluminum pop rivets) for attaching the sheet metal to the doors and window frames. They are tapped into the 4130 tubing. Just good-n-tite...no locking feature! Could use loct-tite on the screws maybe. That works OK, I suppose and is what I have always done,

But what got me to thinking was Bob recommends using a similiar method to attach the skylite. #6 screws tapped into the 3/8" square tube formers at the wing root fairing. On the skylite attach, I have always felt that the screws should be slightly loose to allow expansion and contraction of the lexan. A big piece of glass like that REALLY does move. I tried putting some loct-tite on the screws that attach the glass on my first Beahawk build, and the glass didn't like that at all! Little star like cracks developed around each screw hole, lexan is not resistant to the lock-tite apparently. So I asked Bob what he did to provide some "locking feature" for the screws. He said when tapping for the screws, to run the tap only partially in, just when you feel it "break through". That way the screws will be tight and provide a locking feature.

Bob also told me he uses aluminum pop rivets to attach the glass in the windows. He doesn't pull them completely to break the stem, just enough to expand the rivet slightly and then cuts the mandrel off flush, touching it up a little with a file or dremel tool. That way the glass is not held too tight and is not crushed even though there is an aluminum back up strip.

[Archer39J]

A lot of RV guys will point to instructions in the RV-8 (I believe) that instruct the builder to run a tap through some seat pan nutplates. I've see this repeated as justification for tapping every nutplate they come across. Probably not a big deal on most things, cover plates and such, but man I really question the thinking behind intentionally destroying standard hardware in that manner.

If you feel you can judge where and when to do this, it's your experiment. It is not good practice.

[BravoGolf]

It is important for us all to understand where and why of any particular fastener system before it is used. I don't know anyone recommending tapping all nutplates. In a few applications it makes sense, but the installer needs to understand the where and why aspect before moving forward. The discussion on Vans was about seat pans and a specific area of the seat pans. Some took that to mean a recommendation for all nutplates. I don't believe that was the intent.