Inspection of STI or helicoil threaded holes. QA concerns

[bob8907]

We are making some parts that require some 6-32 STI holes and we install the inserts. We are inspecting our STI holes and our nogo side runs in about 1-2 turns. Problem is when the inserts are installed, a standard 6-32 nogo gage will go in. I realize it is usually not standard practice to accept/decline parts based on that test but have heard of problems in other situations with inspectors. Obviously coils have their own tolerance so I think the idea is bunk but if my parts get kicked, I stand to lose a BUNCH of time and money. These are EXPENSIVE parts.

Main problem here is our immediate customer will surely accept them but I am more concerned about their customer who may have other inspection "ideas". My question is, do inspectors in aerospace typically drive a nogo gage in a helicoil hole and if it goes, is that really an issue? Would seem this should be spelled out to the letter if so because standard practice is to build the threaded holes to tolerance, then install the coils and use them. I am vry concerned that once they go removing the inserts, they may fail because we have already messed with them while driving inserts in and out of them. Would I have a case here? We may be able to add some build to our chem film coating in the threads to help tighten them if this will be a real issue.

 

[mfgenggear]

Inspection criteria Depends on the specified customers specification.

normal standard practice is to gage the tapped holes prior to installation of the heli coils.

the hole must accept the STI go gage
and not accept the STI no go gage.
these STI Gages are not standard thread gages.
After installation the theads are not gaged.

see link

http://www.helicoil.com.sg/HeliCoil-Gauges-Extracting-Tools.htm

 

[bob8907]

Yes, we gage with an STI gage but we also install the inserts so there is no way to gage the hole after. I was just very surprised to see the standard nogo 6-32 go in the hole.