90 Degree Elbow Orientation Problem

I spent some time to day attaching my brake lines to the master cylinders on the rudder pedals, and ran into a problem.

3 of the 90 degree elbows that screw into the master cylinders would not orient correctly (straight up). In fact, one of them would only orient straight down. Others would only hand-tighten at some angle that is sure to cause interference with the rudder pedals themselves.

What are my options here?

Basically, you should get approximately four tuns to hand tight. You then have two to three more turns with a wrench. Within that last turn, you should be able to 'clock' the fittings. Here's a source: http://www.mechanicsupport.com/articleFittingTight.html

Take one of the elbows to the hardware store and get the right size pipe thread die. Lubricate the die with some oil and thread it on to the fitting by hand until tight and then maybe 1/2 turn more. Rinse it off well before trying it in the master cylinder (you don't want any chips in the brake system!). It does not take much material removal, just barely scratching through the anodising in a couple of spots on the thread will give you all you need.

Stewart Willoughby
RV6, finishing.

Stress risers!

Aircraft threads are rolled, not cut. Don't use a die.

Try a different fitting or swap them to see if you can get the correct orientation. Sometimes it's just trial and error to get a fitting that will orient correctly for your application.

How do they do that?

szicree said:

Aircraft threads are rolled, not cut. Don't use a die.

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Steve,
I'm not a machinist, but I'd like to play one on TV! I know how male threads [like on an AN male fitting] are rolled. I can not envision any way to "roll" a female thread in a hole. What sort of special tooling is used to do that?
Charlie Kuss

Acme universal aircraft thread roller (deluxe model). Really...if those threads are rolled I'm Jimmy Doolittle.

sf3543 said:

Try a different fitting or swap them to see if you can get the correct orientation. Sometimes it's just trial and error to get a fitting that will orient correctly for your application.

Click to expand...

I agree with Steve, sometimes it takes 3 or 4 different fittings to find one that will orientate correctly.

I was told by someone who should know that scotchbriting the threads will allow enough extra turning to solve the problem.

V

Do I detect a little sarcasm?

aerhed said:

Acme universal aircraft thread roller (deluxe model). Really...if those threads are rolled I'm Jimmy Doolittle.

Click to expand...

All I know is that a guy who owns/runs a very well-equipped machine shop that specializes in the production of AN style fittings told me that there are very subtle differences between his stuff and the "real" stuff. Chief among these differences was that his stuff was cut rather than rolled. He also explained that the real stuff has a completely different thread profile with round peaks and valleys rather than sharp. Incidently, he also pointed out that the inner diameter on his are larger to flow more fluid, but that this does make them weaker. Finally, he showed me both through a magnifier and the cut one was quite jagged.

Regarding rolling inner threads, I think it is correctly referred to as "forming" when it's an inner thread. I once saw a device for doing it that sort of looked like a tapered tap. Beyond that I have no idea.

I apologize if anything I said is inaccurate, but I was only passing along what I was told face to face by a guy in a shop apron who seemed to be very knowledgeable in this one area.

Use lubricant, like Fuel Lube, tighten them like you are tapping a thread, tighten, back off 1/4 turn, tighten some more, back off, etc...
If that fails, try a new fitting. They are all a little different for some reason.

Say, Mr. Doolittle...

aerhed said:

Acme universal aircraft thread roller (deluxe model). Really...if those threads are rolled I'm Jimmy Doolittle.

Click to expand...

Here ya go: Female thread forming.



http://www.balax.com/catalog/thredfloer-taps/thread-forming-vs-cutting

Best,

Thanks Pierre, I've seen those before. I just didn't think the threads in that master cylinder were formed or rolled because sitting in that sharp counterbore under the anodizing they always looked real "crispy". Guess I over-jumped.