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Machine screws seem longer than necessary

AeroDog

Well Known Member
Friend
Throughout the build it seems that there are machine screws which are longer than necessary. For example, in the tailcone fiberglass fairing there are 20 AN526C632R8 screws which are 1/2 inch long. Using an AN526C632R6 which is 3/8 inch long leaves 4 threads showing after being screwed into the nutplate. Is there some reason for the extra length?

Jerre
 
I bought some MS35206-228 from Aircraft Spruce for the instrument panel. Not only are they shorter,
but the Philips heads do not strip out easily like the original screws.
 
if you are going to the trouble of ordering screws i went to mc master carr for torx head for the panel. i don't think phillips would strip but originally i used allen heads. i can tell you they are a problem and i had several strip the head while attempting to remove. torx head were ok.
 
Just a question here: for the RV 12 LSA, are you allowed to use shorter screws that work vs the longer screws that are called out?
 
if you are going to the trouble of ordering screws i went to mc master carr for torx head for the panel. i don't think phillips would strip but originally i used allen heads. i can tell you they are a problem and i had several strip the head while attempting to remove. torx head were ok.

I just looked at McMaster-Carr and all the torx flat heads they have are 82 deg. All the phillips flat heads supplied by Van's are 100 deg, and that's also the angle of dimple dies. If you want to use those 82 deg torx, that's great, but realize you can only use them where you have enough thickness to use a countersink (which for an 8-32 with undercut head, is min .070). I've never seen an 82 deg dimple die.
 
i never dimpled [ or countersunk]my panel when i made it from scratch. never thought of that when i posted.
 
I just looked at McMaster-Carr and all the torx flat heads they have are 82 deg. All the phillips flat heads supplied by Van's are 100 deg, and that's also the angle of dimple dies. If you want to use those 82 deg torx, that's great, but realize you can only use them where you have enough thickness to use a countersink (which for an 8-32 with undercut head, is min .070). I've never seen an 82 deg dimple die.

You can get 100 deg flat head Torx here.
https://www.microfasteners.com/home.php?cat=620
 
In order to register an RV-12 as an E-LSA, it must be built exactly per the plans using only parts supplied by Van's.
 
I think Joe makes a good point. The regs make it pretty clear, but from an engineering standpoint the threaded shank that extends beyond the nutplate doesn?t do anything for you. License it and then use good judgement for any minor deviations that make sense.
 
I think VANs pretty much tries to keep the different part type counts down so you may see some screws a little long for some applications. (Just a guess.)
Using a machine screw is different than an AN bolt where the one to three threads showing rule of thumb is used in order to keep from tightening a nut down onto the grip of the bolt but leaving the bolt loose in the assembly.
Since the machine screws are usually threaded all the way to the head, it doesn't really matter if they are too long as long as you have a thread showing on the nut.
I don't remember where, but it is discussed in the 43.13-1B Acceptable Methods Guidelines publication.
 
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