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  #11  
Old 10-19-2018, 06:39 AM
Deweyclawson Deweyclawson is offline
 
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Quote:
Originally Posted by Aluminum View Post
A better way to accomplish the same is with loctite, for instance on the spinner and other highly cycled places.

It is safe to run a tap through almost all nutplates.
I am certainly not an expert on any of this but I would just like to pass on my experience.

Over the last 3 years the screws on the spinner have gotten worse about being loose after every flight. At first it was just one or two. Lately almost every screw in the forward ring were loose after every flt. I tried loctite to no avail. It did help at first but then they still came loose. We just did the annual insp and I replaced all 12 nut plates in that ring. 12 hours and five flights later and they are all still tight.

Some of the screws in the seat pan were very tight so I tried the Boelube trick. That worked for most of them but some were still tight. I ran a tap thru them and that made it much easier. None of the seat pan screws come loose from one year to the next.

I would have to say that this statement is correct:

"Defeating the locking feature of the nutplates by running a tap through them defeats the designer’s purpose in putting a locking nutplate there. In some cases, this is OK - but only in some cases. If you do it indiscriminately, without understanding how aircraft are designed, you’re really butchering the project." - Ironflight

Remember that you are going to be the experimental test pilot every time you fly.
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  #12  
Old 10-19-2018, 08:00 AM
Jimd Jimd is offline
 
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Don't know if it helps, but about two weeks ago I made a video of how I install nut plates. What helps me (my tip) is cutting off a screw that is used to install the nutplate. This helps insure that it is in line with the parts once riveted which helps avoid binding from mis alignment. I also use boelube on the new full length screw at final assembly.

https://youtu.be/X6mvsGOSICU

Jim
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  #13  
Old 10-19-2018, 09:47 AM
Tom Martin Tom Martin is offline
 
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There is a lot of talk about nutplate hole misalignment . I built my first two planes using the nutplate itself as a hole template. It certainly does work but takes a bit of extra time to get all the holes done. Most of the nutplate holes are already drilled on the RV14. On my third and subsequent planes I used a nutplate jig. It is the bomb. Much faster and very accurate.
As for the tapping vs not tapping, there is not a real hard and fast rule. Yes of course it would be nice if all the nutplates were perfect but there are differences. Sometimes just half a turn with a tap will make the screw fit easily in and maintain the locking feature. Yes you should use some sort of lubricant, Bloelube is a good product.
There are some locations where the screws are never going to back out, for example inspection plates in floorboards. It is really nice to not have struggle with tight screws on inspection plates. However this is not a hard and fast rule. I certainly do not want external inspection plates to come loose.
Stainless steel screws have a machined thread and they tend to go in a lot easier. Again in structural areas this might not be advisable. I use quite a few stainless screws on the cowlings, internal inspection plates and to fasten floor boards down etc. Bloelube is still a good idea when using stainless but it is not typically necessary on subsequent insertions.
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  #14  
Old 10-19-2018, 10:08 AM
Aluminum Aluminum is offline
 
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Quote:
Originally Posted by Deweyclawson View Post
Over the last 3 years the screws on the spinner have gotten worse about being loose after every flight. At first it was just one or two. Lately almost every screw in the forward ring were loose after every flt. I tried loctite to no avail. It did help at first but then they still came loose.
Spinner is indeed a special case, as those are the most highly stressed nutplated joints on the entire airplane!

Keep in mind that methacrylate-based threadlockers such as Loctite 242 do need contact with bare metal to cure properly. There are two simple ways to ensure this:

1. Do not reuse the bolt!

2. Run a tap through the nutplate to remove old Loctite and expose the metal.

I must have replaced my spinner at least eight times so far and never had a loose screw--every one gives a satisfying pop when first cracked loose.

Paradoxically, if you must reuse the fastener it is better to simply leave old Loctite on there. Re-applying fresh Loctite when there is no contact with metal results in it not curing properly, and might even act as lubricant to hasten the undoing of the joint. Lots of good info from the experts.

Then, there are different sizes of taps. If you are worried about loss of locking action it is best to buy a "close fit" tap from a proper machinist supply. These are 3-6 thou tighter than hardware-store variety. See here for example.


Good advice from BillL mentioning ACR Ribbed phillips inserts. I've had good luck with these from Brown Tool. They only work for removal though.
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Last edited by Aluminum : 10-19-2018 at 10:13 AM.
  #15  
Old 10-19-2018, 10:16 AM
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Toobuilder Toobuilder is offline
 
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Quote:
Nutplates are not normally used for joints that require the full bolt strength. They do not perform as well as a regular nut whose threads come up to the material. An easy way to tell is if the bolt isn't torqued to spec, as is the case with all phillips head screws holding panels and such. These are what the OP was having trouble with, if I understood well.

It's not the locking of the nutplate that keeps the bolt from turning, that's normally only a small part of the total friction. The locking action can slow down nuisance unscrewing if the assembly wants to vibrate loose, and only after the nominal clamping friction has been defeated. A better way to accomplish the same is with loctite, for instance on the spinner and other highly cycled places.

Lubrication doesn't help if there is physical interference between the misaligned hole and the bolt. A thou of misalignment is practically impossible to see, but will greatly increase friction and cause galling and stripping. Running a tap takes care of this and doesn't damage the nutplate.

It is safe to run a tap through almost all nutplates.
The above is contrary to the process specifications of the large aerospace company I work for.

There are many, many varieties of self locking nutplates and many of them share the properties of, and are direct replacements for nuts in both tension and shear applications.

The free running torque is the "locking feature" of the fastener. Once that running torque is no longer meeting specification the nutplate is junk. Most nutplates are expected to last 5 cycles and still meet spec. There are also "long life" nutplates that can go longer in field service. Of course we are not held to this standard with E-AB, but aircraft OEM's take this stuff seriously. We replace low running torque nutplates by the hundreds when our airplanes return to the depot.

If one has physical interference due to misallignment, the nutplate is installed wrong. Simple as that.

Running a tap through a nutplate removes material from the mechanically distorted portion and eliminates the self locking function as well as weakening the fastener itself. There are circumstances where this is acceptable, but saying this situation is categorically "safe" for almost all nutplates is incorrect.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

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Last edited by Toobuilder : 10-19-2018 at 10:28 AM.
  #16  
Old 10-19-2018, 10:34 AM
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Mel Mel is offline
 
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Quote:
Originally Posted by Toobuilder View Post
The above is contrary to the process specifications of the large aerospace company I work for.
There are many, many varieties of self locking nutplates and many of them share the properties of, and are direct replacements for nuts in both tension and shear applications.
The free running torque is the "locking feature" of the fastener. Once that running torque is no longer meeting specification the nutplate is junk. Most nutplates are expected to last 5 cycles and still meet spec. There are also "long life" nutplates that can go longer in field service. Of course we are not held to this standard with E-AB, but aircraft OEM's take this stuff seriously. We replace low running torque nutplates by the hundreds when our airplanes return to the depot.
If one has physical interference due to misallignment, the nutplate is installed wrong. Simple as that.
Running a tap through a nutplate removes material from the mechanically distorted portion and eliminates the self locking function as well as weakening the fastener itself. There are circumstances where this is acceptable, but saying this situation is categorically "safe" for almost all nutplates is incorrect.
Very well stated. Please listen to what Michael says. Platenuts are designed the way they are on purpose. Don't destroy that purpose.
Personally I use the "wax" lube method for initial threading into a new platenut. A toilet bowl wax seal ring is cheap, works great, and lasts a long time.
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  #17  
Old 10-19-2018, 10:34 AM
jask jask is offline
 
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Default screw

you can buy allen head screws from McMaster-Carr
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  #18  
Old 10-19-2018, 11:10 AM
Aluminum Aluminum is offline
 
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Quote:
Originally Posted by Toobuilder View Post
There are many, many varieties of self locking nutplates and many of them share the properties of, and are direct replacements for nuts in both tension and shear applications.
I don't doubt that this is true, but our run-of-the-mill K1000-08 nutplates almost certainly don't fall into this category. It's good that you called me on it as I went to find the tensile/shear spec for these and can't seem to dig up an authoritative source. Perhaps someone can link if you know of one? Some vendor sites list 700 lbs yield spec for the -3 size, which is significantly lower than ~2000 lbs for a regular AN3 assembly, as I would expect just from looking at the fragile little thing.

Quote:
Originally Posted by Toobuilder View Post
The free running torque is the "locking feature" of the fastener. Once that running torque is no longer meeting specification the nutplate is junk. Most nutplates are expected to last 5 cycles and still meet spec. There are also "long life" nutplates that can go longer in field service. Of course we are not held to this standard with E-AB, but aircraft OEM's take this stuff seriously. We replace low running torque nutplates by the hundreds when our airplanes return to the depot.
I hear ya. The reality is that keeping to that spec would make almost every E-AB in existence non-airworthy, at least among the ones I've been around so far!

Quote:
Originally Posted by Toobuilder View Post
If one has physical interference due to misallignment, the nutplate is installed wrong. Simple as that.
Agreed. Again, this is a fairly common occurrence in amateur hands.

Quote:
Originally Posted by Toobuilder View Post
Running a tap through a nutplate removes material from the mechanically distorted portion and eliminates the self locking function as well as weakening the fastener itself. There are circumstances where this is acceptable, but saying this situation is categorically "safe" for almost all nutplates is incorrect.
Well, the only categorically true statement is that any advice you read on teh internetz is worth exactly what you paid for it.

I see that our little "run a tap through it" camp has polarized the discussion, but the result has been very educational so let's leave the discussion here for posterity.

FWIW, I posit that lubricating the fastener also reduces the locking function, perhaps in an even worse way than mild re-cutting, as the re-cutting won't remove all locking--the nut will expand around the tap.
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  #19  
Old 10-19-2018, 11:10 AM
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az_gila az_gila is offline
 
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Quote:
Originally Posted by BillL View Post
So the running-a-tap-though debate aside, if you are stripping the drive heads, that is another long running issue. Just use drive bits, preferably an ACR bit. I found (finally) screw drivers typically are highly inferior to the driver bits (except the $$$$ ones). I only use the bits now and seldom strip a head, and never on the first use. Do a search on VAF and several threads will come up.

......
I found that replacing the usual AN515 screws that are rated at 60K psi tensile with more structural screws, such as these at 125K psi - I like the washer head look inside the cockpit for floor/bulkhead attach -

https://www.aircraftspruce.com/catal...ages/an525.php

Or these at 160K psi tensile - normal head shape -

https://www.aircraftspruce.com/catal...ges/nas600.php

Or even these if the hex head helps access, at 160k psi - really helped in a few spots on the -6A on the floor stiffeners and firewall -

https://www.aircraftspruce.com/catal...es/nas1801.php

Or these at 125K psi, but you have to allow for grip length -

https://www.aircraftspruce.com/catal...es/ms27039.php

All of the above are made from a stronger steel and seem to last longer and get less bugg**ed up with philips head screwdrivers.

PS also use Boelube for the first insertion and I have never run a tap through a nutplate.
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Last edited by az_gila : 10-19-2018 at 11:13 AM.
  #20  
Old 10-19-2018, 11:38 AM
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rzbill rzbill is offline
 
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Quote:
Originally Posted by Aluminum View Post
I hear ya. The reality is that keeping to that spec would make almost every E-AB in existence non-airworthy, at least among the ones I've been around so far!
So..... that is an indication to me that entirely too many nut-plates are being tapped.

During my build, I tapped exactly...zero. It is not needed. Use of good installation technique and proper tools address most. A little whale oil (Boelube) or wax fixes the few tight ones.
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