ADDING THREADS TO BOLT 9

[AIRFRAMER]

I HAVE 8 BOLTS FOR A MAIN LANDING FULCRUM THAT ARE TO LONG IN GRIP LENGTH, THE PN# IS MS21250-08-76 AND I NEED A MS21250-08-74, I HAVE LOOKED WORLD WIDE AND NOTHING CAME UP, THE ONLY ONE CAME UP WAS THE -76 AND I ALOSE INSTALLED SHIMS AND THE MAX WASHERS STILL THE NUT BOTTOMS OUT, WILL THERE BE ANY PROBLEM ADDING 2 THREADS. OR DOES ANYONE KNOW OF A ALTERNATE PN#, I ALSO LOOKED AT NAS628-74, NO JOY. THIS IS FOR P3C ORION A/C THANKS

 

[wes616]

Can you not shim with another (thicker) washer(s)? What is your complete fastener stack? I would advise against adding additional threads; in lieu of machining additional threads, consider a custom spacer(bushing). Also, are you using this ms21250 due to the tensil 180 to 200 ksi?

Wes C.
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No trees were killed in the sending of this message, but a large number of electrons were terribly inconvenienced.

 

[Rob130]

I would also caution against adding threads. The specs for your bolt most likely are UNJF threads, which means they are rolled threads, not cut. If you use a die (UNF) to add threads you will not only reduce the tensile strength of the bolt but also remove the cadmium plating from the shank.

Using a UNF die will change the geometry of the thread root to a point \/ and not have the smooth radius of the UNJF thread. Stress riser + reduced corrosion resistance = Trouble in the future.

 

[Rob130]

I forgot to add the TO 1-1A-8 is incorrect when it shows UNF threads for all aircraft bolts. The specification for the bolts will state rolled threads. Try this. Take one of the old bolts and run a die down the threads. When you are done you will have metal filings result. That is because the UNF die cut into the radius of the UNJF threads.

 

[rb1957]

like rob above, i'd advocate extreme caution. i'm assuming you're dealing with the main landing GEAR.

your -76 screws are 1/8" longer than the -74 (i'm surprised that the world support of P3 hardware is zero ... but then maybe it's more that you need something NOW). i'd add 1/16" washers under the head and under the nut, in addition to the B/P washers ... this is only a single size change in hardware which is usually acceptable, these are BIG screws (5+") so this is a small change to the bolt.

if you pack an extra 1/8" and the nut still bottoms out, then maybe something else is amiss ...

 

[plasgears]

Never generate new threads on a rolled thread fastener. You will cause grief and gnashing of teeth.

In specific terms, failure will occur at the new threads and at a lower strength than expected.

 

[Stache]

You can contact the Technology Transition Office and they can find the bolts you need. If you have the part number or national stock number it will greatly help them. This office is a wealth of information.

Tech Connect
Technology Transition Office
AFMC TTO/TTR Bldg. 22N
2690 C St STE 5
Wright-Patterson AFB, OH 45433-7412

1-800-203-6451

Stache

 

[AIRFRAMER]

HEY THANK YOU GUYS FOR THE INFO, BUT I STILL CAN'T FIND THESE DARN BOLTS, AND ARE THE NAS628-74, AND THE MS21250-08-074 THE SAME BOLT, I HAVE LOOKED ALL OVER, AND THIS A/C HAS BEEN DOWN NOW 38 DAYS, STILL NO BOLTS, OUR SUPPLY LOOKED ALSO AND THEY FOUND A COMPANY BUT NOW THEY SEEM NOT TO HAVE ANY, I AM REALLY NEED OF SOME HELP ON THIS SITUATION. THANK YOU

 

[Fabrico]

Have you tried Coast Fabrication? They carry lots of aerospace fasteners and do aircraft quality bolt thread rolling.

http://www.coastfab.com/product sevices.html

 

[WKTaylor]

Airframer... DO NOT DO THIS UNLESS YOU ARE A CERTIFIED FASTENER EXPERT.

Manufacturing aerospace fasteners is NOT a trivial operation. Every fastener is fabricated to a procurement specification, which includes extensive testing for EVERY production run of parts. Altering an existing fastener immediately cancels the certification of the fastener, since it no longer conforms to the “as fabricated state”. The reasons for this critical accounting for “standard fasteners”, exists due to the documented in-flight failures of standard parts that were fabricated and/or altered improperly and “sold” as genuine-to-the-spec parts.

Altering threads implies affects on the thread metallurgy, thread-form/tolerance and thread coating-system… just to name a few of the critical aspects involved. These factors in-turn affect not just static strength, but also fatigue durability, corrosion resistance, installation preload [minor thread thread-form differences will affect torque/pre-load], etc.

Minor modifications, such as drilling locking-holes thru the thread or head to match the part specification MAY be acceptable, since these are minor operations that could be accomplished before or after the basic part has been fabricated [including application of protective coatings]. However, such actions, do require engineering authority to accomplish, IE: liaison signature, a note on an engineering drawing, or a unique drawing dedicated to the altered part. We can also do more radical alterations to parts, such as shaving heads or shortening threads, etc [typically for structural clearance or weight savings] … however the parts NO LONGER conform to the original type certification: hence it is usually given a unique drawing number [x-xxxxx-x] that has been certified by [signed-off by] engineers with design, materials and stress authority and includes detailed instructions for this work.

I direct Your attention to NAS4002, NAS4003, NAS4004 and NAS4007, as an example of fabrication requirements for a typical series of moderate strength external threaded fasteners. There are several related Boeing specs for bolts made per Boeing specs… and related NASMs for much higher strength parts. Also, MIL-HDBK-1599A, Requirement 107, has a fairly complete/compact discussion relative to altering standard parts.

Note: for every production run of standard threaded fasteners, there are destructive testing requirements. The minimum production run is typically 10 fasteners: (9) randomly selected for destructive testing/evaluation… and (1) for actual sale [use].

If this were a war-critical requirement (battle-damage recovery, etc) I would not hesitate to recommend altering fasteners for specific short-term use. However, these deviations from accepted practices in routine maintenance operations have a bad habit of proliferating to become standard practice … and the parts often become “lost” [untraceable], very quickly. [Untraceable = Danger]



Regards, Wil Taylor