G

gstone

Well Known Member
I have to thread aluminum for a few #6 screws to hold fairings on my Rocket. Any tricks for this and is AN better than stainless for corrosion?

Thanks for any help!
Greg
 
Use something like Rapid Tap for cutting fluid and go slow. Make sure you use the correct pilot drill size.
 
When you tap them....

Try rubbing alcohol to keep the chips clean and cutting smoothly! ;)
 
gstone said:
I have to thread aluminum for a few #6 screws to hold fairings on my Rocket. Any tricks for this and is AN better than stainless for corrosion?

Thanks for any help!
Greg
Click to expand...

Yes, Cad plated steel hardware [AN] will not cause corrosion of your skins. The plating is a sacrificial material. If you are into boating, it's like the zinc bolted to the outboard motor or the out drive to protect the aluminum from corrosion. Over years or decades, it will get used up. At that point, you will need to replace the fasteners. See

http://www.eaa1000.av.org/technicl/corrosion/galvanic.htm

2024-T4 [not sure if that's a misprint] is #24 on the list. Any metal below #24 placed against it, will cause corrosion of the 2024. Any metal higher on the list, will corrode first.

Charlie
 
SAE/USS

Thread inserts are a good way to go. Commonly used AN fasteners are SAE threads, 10/32 for example, and are generally not good for use on aluminum or even cast iron. USS threaded AN fasteners are available but hard to find. Inserts installed from the git go may eliminate future problems.
Tim
 
One important thing to keep in mind is that 6-32 is the very weakest tap size. That is because the minor diameter at the thread root is a greater percentage of outside diameter than for any other common combination of shank diameter and thread pitch. Use a good quality tap, and work slowly and carefully so you don't break the tap off inside a longeron and have to go in and dig it out.

Thanks, Bob K.
 
More great info...

Thanks Stoo, I'll order a couple in the morning! Bob, I've had trouble with the very thing you are talking about but really trying to minumize the hole size of the hole, might look at going up to a #8???

Thanks again all!!
 
WD-40

Greg,

If you are only doing a few holes, as others have mentioned (right pilot drill, good tap,etc) but just use some WD-40 to lube while tapping the hole. It will work great....no need to buy any special tapping fluids....it will give you a nice new set of "threads"! :D
 
how thick?

How thick is the aluminum? I would avoid doing it if you could install nut plates or clipnuts instead. There is also a device called a rivnut that may be better. The tapped aluminum will eventually deteriorate,as well as not having any retention or self locking quality. Steel screws into aluminum will eventually lead to corrosion, no mater what coating it has...I specialize in corrosion prevention on heavy aircraft overhaul.
 
Guessing...

I think about .25 inches. Will try to look at it closer today. It's in the lower corner and need to put the fairings on the bottom. I don't want to drill this area any larger than needed and won't have to hold much... ?????

Thanks!!
 
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taps

There is a kind of tap that forms instead of cutting. I believe it's a little stronger than a cut thread. It does take more torque to turn but no chips. Never used dry. Has a different size drill than a cut tap it a fraction bigger than a cut tap drill. Great to used in a hand drill if you have a lot of holes to tap at one time.
found this on line.
THREAD FORMING TAP*These taps are fluteless except as optionally designed with one or more lubrication grooves. The thread form is lobed so there is a finite number of points contacting the work. This tap does not cut, so it is 'chipless', and consequently will not cause a chip problem. The tool forms the thread by extrusion, thus thread size can be closely maintained. The fluteless design allows high quality threads, faster tapping speeds, higher production, and generates no chips which simplifies tapping of blind bottoming holes (threads can be formed the full depth of the hole).
Bill J
 
I'm not sure what you are drilling into, but there isn't anything that fairings attach to in an RV made from aluminum or steel that thick....maybe you need to post a picture.
 
It's been a while since I looked at this.... Just had planned on tapping the holes and the material was pretty thick but even with a heavy longeron and the skin it wouldn't be that thick... More like .125-.150 buy will come up with that tomorrow for sure! It's a Rocket but not that much difference probably.... Edited previous!

Thanks!
 
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Skykingbob said:
...just use some WD-40 to lube while tapping the hole. It will work great....no need to buy any special tapping fluids....it will give you a nice new set of "threads"! :D
Click to expand...

WD-40 is not a lubricant and has no place around an airplane. IMNSOHO

I used TAP Magic because the store where I bought my taps gave me a can to try. As long as you use some kind of cutting oil, you will be OK.

Just remember to turn the tap a little bit, back it off until you feel it break the chip off and then turn it some more, back it off, turn some more, back it off, etc.

Go slow and use the proper drill, as others have said.

BTW, I used SS screws with no issues.
 
Just finished today, easy job with the hoz off

Did that today myself. No issue using some oil and a clean tap. Just use the proper drill size and keep the tap in line.
Don't sweat it too much. If you are worried about corrosion or screw it up you should be able to use a click bond fastener on the inside.
 
As a general rule, you should never use cut threads in any load bearing structure that is subject to cyclic loading (an airplane). Has to do with durability and damage tolerance analysis, i.e. how cracks grow out of stress raisers, in this case the cut threads.
 
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