So some of the guys in the shop have had a rough time installing helicoils properly and we've had a lot to do lately. I was wondering if there was any tribal knowledge out there for installing thread repair inserts of any kind.
Do you have a trick?
Special prayer?
Custom tool?
Make sure you mention if you're talking about helicoils, timeserts or whatever your favorite flavor of thread repair is
If you can't just be lazy and over-tap to the next size: I prefer helicoil style products. I buy cheapo kits in the red-boxes, and "real" helicoil brand stuff. First, I find the cheapo kits to have preferable inserts, usually having easier breaks on the locking tabs, and being MUCH easier to start and remove if need be. Throw away the cheapo bits, obviously junk.
Big issues is having the correct bit, a quality one. 21/64 is the m8x1.25 insert bit for instance, have 2 if you use that size, US made is the best I've found, and I'm no fanboy. I like high moly and any fanciness I can get. You're drilling at mediocre angles, with a hand drill. Feeds and Speeds need not apply.
If you're dealing with a through hole (debris can escape the other side), tapping is gravy. As a general rule, I prefer not to use cutting oil for inserts, as I am paranoid it could effect grip via the locking tab. Tap it straight obviously. For blind holes, compressed air will often not remove all chips, and the bolt can bottom and snap. Use grease on the tap to help prevent chips from falling into the bottom. Clean afterwards, again, my paranoia. A big mistake I see is guys backing the tap out too early. You don't need to really start clearing chips until that first full thread starts sinking in. Constantly backing up when starting the tap can lead to wallowed out holes on soft material.
If it is holding a fluid behind the helicoil, use RTV on the outside of the insert. YMMV, I usually don't recommend doing so unless a large sealing washer can also be used. Helicoil brands **** with their insertion tools. Use the "?" mark shaped tool from the cheapo kit. Don't let the insert skip threads going in. Helicoil brand stuff is way harder to pick out if this happens, and can tear up threads in soft materials. Mild down pressure is required, it's a balancing act with not having it skip threads. Going through the threads thoroughly with the tap helps a clean start.
Break the tab off, expecting you will not be able to retrieve it. I usually drill a bit deeper if I can, to allow a small debris chamber to exist. You're not likely to even vacuum 100% of it out, so prepare for this. Another big one is test fitting the bolt before tightening. Sometimes you cannot drill deeper, nor extract all debris. Thus, the hole is now shallower, adding a washer usually fixes that up.
