Re: Helicoil/Stellings extension box
 

A KEENSERT uses two to four staking pins that are hammered in place after the insert is installed to prevent it from backing out. LOCKTITE is not needed.
I use these in my vibration test fixtures. The inserts (KEENSERTS) that are currently installed have endured as much as 1000 hours of 6+ G's vibration testing at 2000hz frequency. Along with repeated disassembly and reassembly.

Not sure what TIMESERT is, Don't think I've ever seen one.

Forget the RIVNUT idea. They are meant for low strength sheet metal applications. And if not installed correctly they spin when trying to tighten the fastener.

A HELICOIL will probably work as long as you get the type that has the locking adhesive on them. A special liquid primer is needed to activate the adhesive after assembly.

Re: Helicoil/Stellings extension box
 

Re: Helicoil/Stellings extension box
 

Mine are all 5/16 X 1" SS. No more issues. You can also thru bolt one side. When removal is necessary, you can access the nut from the other side. This can be good short term fix.

Re: Helicoil/Stellings extension box
 

Thanks for the link Scott.
That's one I haven't seen before. Looks like it requires a little maching for the top lip to seat at, or below, flush.
I have seen an insert that has, what looks like, a screwdriver slot across the top. That's what I thought this one was.

Thanks.

Re: Helicoil/Stellings extension box
 

Let's define "high vibration" in this fastening application. By high vibration, I do NOT mean that they aren't good to use on something that will vibrate as a unit. I mean they aren't good to use on something that the two pieces being fastened are prone to move against each other (like an outdrive application). As we all know, aircraft parts are OVER designed by a large factor. Fastener size, length, stretch, and fatigue life are all considered and are part of the sizing calculations they use. An outdrive can and WILL creep around a bit under hard usage.

Since a Helicoil is a stainless steel spring with a diamond shaped cross section, if installed in soft material and asked to support a high load under vibrating (creeping or moving) conditions, then the spring can "roll" in the supporting material and begin to self-loosen. As it twists even a small amount, it begins to deflect the fastening forces outwards, compounding the situation. Some applications are in thin webs that do not have enough base metal to allow a full insert (Helicoils require a smaller hole OD than an insert) and in those cases, Helicoils are the best option. Another thing that makes Helicoils "good" is that they self-align. This means that you or I or your wife can drill and tap a Helicoil hole with hand tools and it will still manage to align itself relatively well with the fastener when torqued. This "benefit" is a drawback in a max-strength application.

A Keensert DOES have hardened "tangs" that will lock it in place. I usually consider the application and if it requires max strength, I will remove the tangs and use the green Loctite unless it is in a very very hot area (heat softens Loctite).

Timeserts are sometimes hard to find. But I like them best. (and I still use Green Loctite on them).

Helicoils are BETTER than the original threads in an average everyday aluminum casting. They require less removal of the original material and preserve web strength in thin casting sections.

But I have a $3000 (that's what it would take to replace it) PWC cylinder on my workbench that has 4 helicoils pulled out of it by the head studs. It's having to get two chunks cut out of the original casting and chunks of aluminum welded back in because as the Helicoils twisted in the grooves, they exploded the sides out of the support posts in the casting.

It's getting TimeSerts when it goes back together.


And Green Loctite.

mc