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heli coil install

Posted by rbigg (My Page) on
Mon, Jul 19, 10 at 1:02

I've read several articles on heli coil installation. I have a 1/4" x 28 that has broken off. I'm thinking about heli coiling it. Got some questions for the machinist in this group:

a. The kit I think is for that says I should use a 17/64 drill. This, of course, is bigger than the 1/4" hole. Does this size sound right? If this is right, then it drills out the thread, plus a little material.

b. So, what is the threading device I should use? Sounds to me like it would be slightly bigger than the 1/4" tap I'd normally use for a whole of 1/4".

Is this the way I'd get 1/4" bolt to fit in?

The reason I'm asking is that my 1/4" hole has a broken pice of bolt all the way in there. Let's say my shaft length on it is 6/8", and the broken piece all the way in there is 3/8".

The problem I would have had was how to get the broken part out. One way is to use a drill slightly below 1/4" threads, and drill it. That still would leave a little in the threads.

I might get an easy-out, but not sure if they make one that small or not.

With drilling the full thing out, I would feel much better about it getting everything, and being ready for the heli coil, all in one smooth operation.

Follow-Up Postings:

RE: heli coil install

Can you post a picture of the matter or link? loger

RE: heli coil install

I ideal situation would be to drill small hole in the center of the broken bolt. then set up to just under 1/4. The tap the threads cleaning out the old shank without heili-coiling it. The problem with it being broken of down inside the hole you can grind it flush and get square flat surface to find the center. If not flat usually the drill bit will go off center. Either way try to drill the piece out first and use a pencil grinder to remove any off center metal so you can try to tap the little bit of remaining threads. What ever you do don't break the tap off. If you do it will be twice as hard to get that out. Use plenty of lub. and go slow clockwise then counter clockwise. The heil-coil kit will have a larger drill bit to so you can install the heil-coil and still have 1/4" threads when the heil-coil is installed


Options: (drilling dead center is your challenge)
1. Drill out very close to the threads and you can usually get the remainder with needle nose or pick.

2. Drill 5/32" and use an extractor (which are that small.

3. Drill with a reversed drill bit in reverse and it usually comes out (lightly oiled).

4. The helicoil would be my last option work wise.

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