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Thread: Blind hole helicoil insert

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    Default Blind hole helicoil insert



    Need to repair and tap a blind hole for a thread insert. I have some experience with the typical helicoil...but only in through hole. I realize I will need a different tap than my tapered one as its a shallow hole. I will need one with a square blunt end. Two questions...
    1) should I start the tap with my tapered one and then switch to the blunt nose...or should I just start with the blunt nose. Its in an awkward location and am worried about keeping the tap nice and square.
    2) is a typical helicoil ok for this application with the little tab I will need to break off on the bottom end?

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    Default Re: Blind hole helicoil insert



    If the hole is deep enough to allow it I'd start with the standard tap, they are easier to start and get straight.

    No idea about the helicoil, I have never used one.

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    Default Re: Blind hole helicoil insert



    I'll second Michael's comment.

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    Default Re: Blind hole helicoil insert



    newracer previously posted:
    "If the hole is deep enough to allow it I'd start with the standard tap, they are easier to start and get straight."

    Seems to be standard procedure...start with the tapered tap, then go to a plug tap, then go to the final flat ended 'bottoming' tap. The biggest hassle is finding the taps, as heli-coils don't use standard tap sizes. Most heli-coil kits come with the appropriate tap for that particular size heli-coil - and most kits only have the tapered tap. The blind hole is about 1/2" deep for 1/4"x20 bolt thread.

    Guess we are going to find out if I can get it to work - have to re-tap my oil pump mounting and the pump doesn't have the clearance to make the mounting holes bigger. I took the pump off as the gaskets have been leaking a lot of oil - think I found out why. One of the mounting bolts was completely useless and pulled out all the thread.
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    Default Re: Blind hole helicoil insert



    In a pinch you might "convert" a taper tap to a "somewhat" bottom tap by grinding the tapered tip off.

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    Default Re: Blind hole helicoil insert



    Jim previously posted:
    "In a pinch you might "convert" a taper tap to a "somewhat" bottom tap by grinding the tapered tip off."

    yes apparently this can be done with care
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    Default Re: Blind hole helicoil insert




  8. #8
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    Default Re: Blind hole helicoil insert



    Jim previously posted:
    "In a pinch you might "convert" a taper tap to a "somewhat" bottom tap by grinding the tapered tip off."

    Specifics from a professional machinist on this technique...honestly I am not sure exactly what a spiral grind on one of the flutes means - but will clarify. I think I will take a closer look at a proper bottoming tap to see if it makes sense. Lots to learn about machining....
    Take the tapered tap and grind the end off back to where the thread starts to get straight. Once you have done that remember the cutting edge is the forward edge of something turning clockwise when looking down from the top. Now that you know where the cutting edge is pick one of the flutes and make sure to grind the material away in a spiral manor on the end in the direction that leaves one flute as the primary cutting surface. You donít need a lot of spiral maybe 5į or so. In other words the flutes will then cut in succession 1 after another. If you look at the end of a bottoming tap you will see this immediately. You donít want all flutes cutting equally at the same time it puts so much load on the tap it breaks.
    ___________
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