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Helicoil use

Helicoil use

Helicoil use

(OP)
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?

RE: Helicoil use

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

Regards,

Mike

RE: Helicoil use

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

Regards,
Rusty

RE: Helicoil use

cadman01,

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

               JHG

RE: Helicoil use

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.

RE: Helicoil use

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.

RE: Helicoil use

Quote (flash3780):

...

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

RE: Helicoil use

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...

RE: Helicoil use

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.

RE: Helicoil use

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

RE: Helicoil use

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).

RE: Helicoil use

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.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Helicoil use

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.

RE: Helicoil use

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.

RE: Helicoil use

(OP)
Thanks all,

I think I will go with rivnuts.

RE: Helicoil use

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.

RE: Helicoil use

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?

RE: Helicoil use

You might want to take a look at "Flowdrill".
The device creates a boss the can be form threaded.
They sell the thread forming tools too.

RE: Helicoil use

without knowing anything at all about what you are trying to do.  Can you glue (bond if you don't like the word glue) them together, or glue piece on that allow for much better threaded connection?

RE: Helicoil use

Glue (bonding) makes a difficult field/hanger replacement problem.

More time in the hanger = More expensive repair.    

RE: Helicoil use

But you can glue pieces to one or the other that allow a proper bolting is what I'm getting at.  Glue bracket to the tubing and thru bolt the plate as an example.
And since you don't know the configuration any more than I do Its really hard to comment on the idea.  I'm more trying to push past the problem and make sure the question is the right one.  

RE: Helicoil use

i think heli-coils in 1/8" thk wall won't work well.

you Could use an anchor nut strip.  it might be a real Fuss to get single a/nuts into a 1" sq tube, but i'm sure you could ... you might start by telling the mechanics that they can't do it !

A suggestion ... now (having designed the structure as tube) isn't the time to ask "how are we going to do ...?".  it's a design detail that should've been understood at the time of the tube decision.  yes, tube looks nice, but a channel would have given you access.

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