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HomeAircraftHelicopterMain Discussion › repairing stripped holes?
11-02-2004 05:22 AM  13 years agoPost 1
shykmaster

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New York

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Hey guys,
anyone know if its possible to repair stripped holes in aluminum.
I just bought a used heli and noticed that the holes in my TDG aluminum seesaw (the center holes) are stripped. Anyway, the seesaw diameter is made to accomadate a 4mm flybar and I don't know if anyone other than TDG makes a replacement. Is this REPAIRABLE?
Thanks
Josh

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11-02-2004 06:05 AM  13 years agoPost 2
YSRRider

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usa

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thats a good question! how much is a new one? im not sure that you could find a HELI-COIL that small so you can rule that out...... a machine shop may be able to weld the hole and re-tap it but that would probably cost you the same as a new one. is it possible you could tap it to then next size screw? i would not trust JB-WELD or a thread repair kit on that.... i would say those are your options.

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11-02-2004 06:50 AM  13 years agoPost 3
heli_headcase

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Hovering around Atlanta

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HeliCoils for Heli's...
I have Helicoils far smaller than 4mm and use M3x.5 Helicoils all the time (for repair of *other* peoples' heli's, not mine ) when threads are damaged. The trick is to be sure the metal is thick enough so the entire lenght of the Helicoil insert can be used with nothing hanging out of either end of the repaired hole. Sometimes I have to carefully trim the insert coil for the correct installed length.

A picture of the damaged part would be very helpful in determining whether it's practical to repair the hole.

Good luck


HHC

So many heli's - too little time...

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11-02-2004 06:51 AM  13 years agoPost 4
TMoore

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Cookeville, TN

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3 and 4mm helicoils are available. I use both in my shop.

TM

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11-02-2004 08:00 AM  13 years agoPost 5
YSRRider

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usa

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really...... im glad i know that now! i think i have some things that i could fix with them!

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11-02-2004 08:02 AM  13 years agoPost 6
Heliscat

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Dublin, CA

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That's nice "others" not mine comment. Don't trust your own work?

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11-02-2004 02:24 PM  13 years agoPost 7
shykmaster

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New York

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cool....What are heli coils and where can I get them?
thanks for all the replies! I'll get some pictures up later today.

josh

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11-02-2004 05:05 PM  13 years agoPost 8
HelicopterJohn

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Seffner, Florida (Just East of Tampa, Florida)

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Cost
I could be wrong but I believe the heli-coil kits are pretty expensive. About $60.00 plus for each size you need.

Let's hear from others on the cost for say an installation tool kit with say a dozen 3mm inserts.

Unless you have a bunch of repairs to make on a particular thread size it is probably not worth the effort. However, if you have a very expensive part to repair it may be worth the effort.

Just something you might want to consider prior to purchasing a Heli-Coil tool thread repair kit.

OC Bob's Gathering #2 was a Premiere Event. Pictures in my Gallery

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11-02-2004 05:19 PM  13 years agoPost 9
z11355

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New England

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yea, the actual repair kit w/ special tap & winder
can run some $$. I think around $70.

All depends on how much stress and extra
material you have.

There are 'Re-Nu' inserts that install w/o special
tools and I know that Loctite (or was it Devcon
or Permatex) make metallic epoxy paste
especially designed to act as an insert.

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11-02-2004 05:39 PM  13 years agoPost 10
Salty

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St. Augustine

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call up a aircraft repair facility at one of your municipal airports...they might be willing to help you out, i know we carry helicoils that small.

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11-02-2004 06:17 PM  13 years agoPost 11
ZIGZAG

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CTRL FL

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Hi
I have used JB Weld with great sucess in alum clean the part verry well
than JB it & let set 24 hours drill & tap
Just a thought
ZIGZAG

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11-02-2004 11:12 PM  13 years agoPost 12
TMoore

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Cookeville, TN

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Actually, there are 2mm helicoils as well.

In industry, helicoils are commonly used when steel bolts are going to be used and high torque specs are called for with aluminum/magnesium/zinc as the base material. You will see this in hydraulic actuators and other assorted parts.

Once an aluminum or plastic part has reached the point of stripping I will helicoil it if there is a considerable cost in the part. Swashplates and washout bases as well as bearing blocks all come to mind.

TM

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11-03-2004 12:54 AM  13 years agoPost 13
heli_headcase

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Hovering around Atlanta

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Heliscat:

> That's nice "others" not mine comment.
> Don't trust your own work?

I was trying to say, tongue-in-cheek, that nothing of mine ever needs HeliCoil repair. You didn't catch that intent. I trust my repairs not to fail.

shykmaster:

HeliCoils are coils wound of a high-strength stainless steel wire. The wire is unique in its cross-section as it's not round but more diamond shaped. The outer wall of the coil perfectly locks into new, oversize threads cut into the damaged part. The inside of the coil accepts the threads of the original size fastener.

Cost of the coil kit can be a factor in suitability of repair vs replacement of the damaged item. I've purchased Australian versions of the HeliCoil repair kit called "Recoil" from Indy RC a few years ago. Cost was close to $35US for sets that included the special tap, install winder, 6 inserts and the tang punch all in a metal box.

As TMoore suggested (and personal experience proved), there's a MIL SPEC requirement that requires a stainless HeliCoil be present in any threaded hole that may see regular "action" in materials that are soft or subject to galling and wear, aluminum in particular.

I will admit to experiencing a major repair failure and maybe I'll post a picture in my gallery of the damage. An OS 32SX-H cylinder head bolt stripped in a friend's engine crankcase. Unfortunately the enlargement of the original hole reduced the strength of the case and it cracked under tension. These were 2.5mm coils.


HHC

So many heli's - too little time...

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11-03-2004 02:01 AM  13 years agoPost 14
rcnuts

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Millersville, Penna

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Ever hear of "Alumaloy"? Its a special alloy of aluminum, available in rod form. It's designed for the average repair person in mind, and can be used to weld aluminum with a propane or mapp gas torch. I must admit I never used it to weld a hole shut and re-tap, but have used it on aluminum castings and sheet metal with total success. Once the repair is made, the fill metal is stronger than the parent metal. PM me if you want more info, or try doing a search on the web. Obviously, if there is any plastic on the piece, this would never work.
Harris,

Hooligan, at large

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11-03-2004 03:47 AM  13 years agoPost 15
shykmaster

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New York

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here is a link to the pics
Thanks for all the replies people. Here is a link to a few photos of the head. If you look closely at the first picture you can see that the screw isn't tightened down. in the other photos you can see the other stuff.

Do you think that they make a heli coil for this size screw. I think it's a #3?
thanks agian,
Josh


Here's the Link: TDG METAL HEAD

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11-03-2004 05:09 AM  13 years agoPost 16
TurboStew

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Ft Collins, CO

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Mid-Grip HeliCoil
There is also a "Mid-Grip" HeliCoil. They have an interrupted (bent) thread about halfway down the heli-coil. They provide a positive lock on the bolt. These are the cat's meow for bolting an MP2 to the header. I put these in high-temp, high-vibration locations straight away.

8.5 pound 90 birds Rock!

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11-03-2004 05:23 AM  13 years agoPost 17
Dr.Ben

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Richmond, VA, USA

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11 pm.

Three day weekend ahead.

Perfect weather forecast for all three days.

You just stripped a critical part. No chance for getting a part shipped in.

You have a helicoil kit on the shelf.

Is it worth the price? YOU BET.

Been there, done this many times.

Ben Minor

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11-03-2004 09:21 AM  13 years agoPost 18
heli_headcase

rrKey Veteran

Hovering around Atlanta

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Are they Pink?
Turbostew:

The anti-shake Helicoils I worked with were a pink or red color to make identification easy. The ones I installed (a few thousand!) were all 2-56 or 3-48 size. They would be a good idea in heli's.

shykmaster:

> Do you think that they make a heli coil for this size screw. I think it's a #3?

I think you mean M3 (3x0.5mm). Didn't you read the thread? You have a very repairable part. The depth of the hole will be very shallow so you would have to modify an existing coil for the correct installed depth. The ends of the coil must be 1/2 to 3/4 of a turn below the surface of the hole after insertion. Not a job for a beginner.

rcnuts:

I'm very familiar with the aluminum alloy repair rod. There are two problems with it when used for fixing small, damaged threads -
1) You can't get down inside a small hole and be sure of a correct bond with the base material.
2) The new material is quite a bit harder than any 'normal' aluminum alloy and this causes any drill to wander away from the repair and into the softer surrounding base metal unless a sharp and short drill is used in a drill press or milling machine. Talking from experience here. You'd be better off going a couple of sizes larger with a tap and gluing (JB Weld, red Loctite) a correctly sized section of threaded aluminum rod into the hole and then drilling it for the original size thread.

Dr.Ben:

Hi!


HHC

So many heli's - too little time...

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