Helicoil use

[cadman01]

I am designing a console to be use in an airplane. The frame of the console is being built using 6061 T6 1"x1" square tube with a .125 thick wall. I have to attach closeout panels and was going to use helicoil inserts. Is there another insert that is common to use or should I stick with the helicoil?

 

[SnTMan]

I doubt a helicoil will work well in 1/8" material, you need to look a a rivnut or similar.

Regards,

Mike

 

[cadman01]

Thanks Mike, That is what I had doubts about, the .125 wall thickness. I will look into using a rivnut

Regards,
Rusty

 

[hydtools]

Used quite a few Dzus captive fasteners in aircraft panels:

http://www.southco.com/landingpages/dzus/

Ted

 

[drawoh]

cadman01,

It might be a little tricky in tubing, but PEM nuts are very good.

JHG

 

[flash3780]

I think that Rivnuts or POPnuts would be appropriate. If you were attaching to a thicker piece of material, I'd suggest a Rosan insert or a Keensert.

Helicoils tend to come out with the screw in my experience.

 

[49again]

Also tricky, but depending on the structural requirements, maybe fish nutplates inside the tube with some wire and secure with CCR 3/32" flush pull rivets....

Steve R.

 

[drawoh]

...

Helicoils tend to come out with the screw in my experience.

That has never happened to me.

Way back a long time ago, I tapped a 1/4-20UNC hole in a piece of scrap aluminium, then I tapped it again and installed a 10-32UNF helicoil insert. I do not know if I achieved full strength, but I could apply lots of torque to my screw.

Are you using the self locking helicoils? I did this on a project, again quite a few years ago, and everyone hated me for it. I have learned my lesson.

JHG

 

[flash3780]

Yes, self-locking helicoils. In a vibratory environment like an aircraft, whatever he uses should probably be self-locking.

I don't mean that they pull out, but rather come out with the screw when it is removed...

 

[KENAT]

We used to use helicoils a lot on aircraft stores and I don't remember helicoils backign out being a frequent problem.

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[flash3780]

Ping one of your mechanics; it's a common problem. Helicoils aren't terrible, mind you, but Keenserts and Rosan inserts are superior threaded inserts. Everything costs, though... so it depends what's in the budget.

 

[drawoh]

flash3780,

Most of my stuff winds up on aircraft, and I do not use self locking stuff. I specify screw torques. I specify lubricating threadlocker whenever I can. I am as confident about my clamping forces as I can be by specifying screw torques.

I have looked into specifying tighening angles, but this requires the systematic scrapping of screws, and I have to persuade everyone else to go along with it.

With self locking fasteners, I have no idea what my final clamping forces are, even if my thread inserts do not fail.

JHG

 

[flash3780]

I did turbine engine design and secondary retention was required for all fasteners (safety wire, threaded inserts, etc.). The OEM had torque/tension data, though I'm sure that it changes as the inserts wear. We were told by the OEM to design for a +/-25% torque tolerance (if I remember right).

I assumed that elsewhere on the airframe vibration was also a concern, though I suppose that the consequences of failure might not be so terrifically bad if, say, the access panel on a console shakes loose (unless you're in fighter jet world).

 

[KENAT]

Pretty much all our stuff had to have secondary retention, we even had a RAE or similar report on what were aceptable.

As to pinging mechanics, we had a lot of ex ordanance guys working there and I don't recall them moaning about helicoils that much.

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[CoryPad]

Secondary retention methods are for physical fastener retention, not for preload retention. If the joint loosens, the fasteners and clamped parts do not spontaneously disassemble.

As to the OP, helical wire thread inserts would be one method, as would key-locked inserts. Rivnuts are definitely a good solution for this particular joint type.

 

[ornerynorsk]

In thinwall tubing, rivnuts will give you superior and long lasting results. Helicoils are not intended for this application.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[cadman01]

Thanks all,

I think I will go with rivnuts.

 

[KENAT]

Sorry, yeah I was a bit off track, for the application I'd doubt helicoils are a good choice, rivnuts or some variation sound better.

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[Tmoose]

When the dimensions are reversed ( 1.5 - 2.0 diameters deep, but with minimal wall thickness ) Helicoils are tough to beat. Much "stronger" than the threads that tore/wore out.

 

[racookpe1978]

Watch your weight: Though this is a small application of only a few added rivnuts, every ounce eventually adds up to that "fatal" 10% loss of range or payload or altitude. 8<)

Even so, it sounds like the best solution. Can you trim the excess 1/8 plate behind the panel where it is not needed for strength near the screws?