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06-25-2011, 09:17 PM
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Join Date: May 2006
Location: Rochester, MN
Posts: 420
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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?
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Rich and Cindy Macrafic
Rochester, MN
Flying
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06-25-2011, 09:40 PM
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Join Date: Dec 2007
Location: Flagstaff, AZ
Posts: 2,653
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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
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Patrick Kelley - Flagstaff, AZ
RV-6A N156PK - Flying too much to paint
RV-10 14MX(reserved) - Fuselage on gear
http://www.mykitlog.com/flion/
EAA Technical Counselor #5357
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06-26-2011, 01:31 AM
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Join Date: May 2006
Location: LL10, Naperville, IL.
Posts: 68
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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.
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06-26-2011, 12:17 PM
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Join Date: Jan 2005
Location: SoCal
Posts: 2,061
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Stress risers!
Aircraft threads are rolled, not cut. Don't use a die.
__________________
Steve Zicree
Fullerton, Ca. w/beautiful 2.5 year old son 
RV-4 99% built  and sold 
Rag and tube project well under way
paid =VAF= dues through June 2013
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06-26-2011, 01:03 PM
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Join Date: Jan 2005
Location: San Antonio, TX
Posts: 1,024
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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.
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Steve Formhals
A&P, Tech Counselor & Flight Advisor
RV3B
RV8
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06-26-2011, 02:00 PM
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Join Date: Mar 2005
Location: SE Florida
Posts: 1,499
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How do they do that?
Quote:
Originally Posted by szicree
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
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06-26-2011, 03:05 PM
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Join Date: Dec 2008
Location: Big Sandy, WY
Posts: 2,567
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Acme universal aircraft thread roller (deluxe model). Really...if those threads are rolled I'm Jimmy Doolittle.
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Actual repeat offender.
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06-26-2011, 03:18 PM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,686
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Quote:
Originally Posted by sf3543
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.
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I agree with Steve, sometimes it takes 3 or 4 different fittings to find one that will orientate correctly.
__________________
Walt Aronow, DFW, TX (52F)
EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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06-26-2011, 06:50 PM
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Join Date: Jan 2005
Location: Victoria, Canada
Posts: 2,251
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I was told by someone who should know that scotchbriting the threads will allow enough extra turning to solve the problem.
V
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V e r n. ====
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RV-9A complete
Harmon Rocket complete
S-21 wings complete
Victoria, BC (Summer)
Chandler, Az (Winter)
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06-26-2011, 10:00 PM
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Join Date: Jan 2005
Location: SoCal
Posts: 2,061
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Do I detect a little sarcasm?
Quote:
Originally Posted by aerhed
Acme universal aircraft thread roller (deluxe model). Really...if those threads are rolled I'm Jimmy Doolittle.
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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.
__________________
Steve Zicree
Fullerton, Ca. w/beautiful 2.5 year old son 
RV-4 99% built  and sold 
Rag and tube project well under way
paid =VAF= dues through June 2013
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