INSERTS, KEY-LOCKED per MS51830E 1

[Aero1207]

We're using a dash size -202 insert in 7050 aluminum. We have the thread in the
aluminum block designed with an undercut at the bottom and the inserts
appear to be threading in and bottoming out past the undercut. We are seeing evidence that
after we drive in the two locking keys, which are being hammered in by hand with the
standard, factory tool that the ID threads are distorting slightly because
the mating part does not thread in easily as it once did. We're not sure if thread distortion is
normal for this type of MS insert but if anyone has had a similar experience please
share. Note, we are getting a press to push the keys instead of hammering.

Another issue we think may be happening is
the locking keys may be generating FOD when being driven home and the build up
of the FOD may be the mechanism that is causing the distortion of the threads. It looks like
by design, this MS type of insert is supposed the chisel off the mating threads
of the part that it's locking into and all of the FOD is supposed to be contained
in the keyway channel. Our biggest fear is that if the insert does not get to a home position
and the keyway channel on the bottom is open, then all of the FOD will freely fall below the insert
and into the manifold. If anyone can shed light on this topic we'd appreciate it.

 

[goodguy1405]

Have you thought about using helicoils?

 

[3DDave]

A couple of suggestions:
1) Are the holes prepped per MS51835?
2) You could use MS51831 inserts to decrease installation distortion
3) Broaching the slots for the keys would give you FOD control. Usually suggested for hard materials, this would help with both distortion and FOD. Fairchild/Tridair makes this tool.

 

[tbuelna]

Did you check to see if you are using a self-locking type insert (MS51830-202L)? The internal locking feature on this insert is a deformed section of thread located about mid-body.

Also, as 3DDave noted above, did you use the correct size tap drill (.332" dia) for the hole threads? The tapped hole for these inserts requires an enlarged minor diameter.

I've installed hundreds of this exact insert in high-strength aluminum and never experienced the problem you describe. The key length on this p/n is .19" which is only 50% of the .375" body length, so the keys should never come close to bottoming out. All of the different MS51830 body materials (303, A286 & 4140) use a common 302 cres material for the keys. While 302 cres is not a high-strength material I have never had a problem with the 302 keys not driving cleanly into an aluminum substrate when using the correct installation tool and a hammer. In the aerospace industry there is a basic requirement for every fastener to employ some form of locking feature, so the self-locking type of this insert is commonly installed in hard materials like titanium or stainless steel. But with hard materials the keyways must be broached with the special tool 3DDave described.

Since the key length is only about half the insert body length, most of the substrate metal displaced when the keys are driven usually remains trapped. However if your application is debris/contamination sensitive, the surest way to eliminate the presence of any loose metallic debris is to broach the keyways and thoroughly deburr/clean the hole prior to installing the insert.

Lastly, in the aerospace industry, due to galvanic corrosion concerns cres inserts are typically installed "wet" into an aluminum substrate using some type of primer or sealant. I imagine the primer/sealant is fairly effective at trapping any metallic debris produced from driving the keys.

Hope that helps.
Terry