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Thread: helicoil fight

  1. #11
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    If you are doing this manually, do not try and drill the 1/64 out. The drill will grab and ruin your day. I would get a 17/64 reamer to open the holes up, even a cheap one will work. If you have the means or a friend with a milling machine, a guide block to keep the reamer straight would definitely be a plus. Good luck, at least the problem has been found.
    Bob Rice #6738
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  2. #12
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    Quote Originally Posted by DCoul View Post
    ...edit: Damn! You're correct BigLakeBob. How am I going to fix this one?! I'm a 1/64 too small!
    DCoul!

    Your Helicoil tap should have already relieved the inside diameter.
    It has a cutting edge ahead of the threads, as do most taps.

    I still suspect the issue is one of depth, not diameter.

    ....Cotten
    Last edited by T. Cotten; 10-23-2017 at 07:15 PM.
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  3. #13
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    reamer.jpg

    I see some that are like a real coarse drill bit and then there is this type. This type looks like it would work best if by hand. Sound right?
    Last edited by DCoul; 10-23-2017 at 07:29 PM.

  4. #14
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    Quote Originally Posted by T. Cotten View Post
    DCoul!

    Your Helicoil tap should have already relieved the inside diameter.
    It has a cutting edge ahead of the threads, as do most taps.

    I still suspect the issue is one of depth, not diameter.

    ....Cotten
    I'm sorry Mr. Cotten but you are incorrect, taps do not size the minor diameter. I am aware they do make a drill/ tap combination for production work but we are not talking that here. Even if what you are saying could be remotely correct, which it isn't, if you read post #3 you will see he took the lead off of the tap. So what you are saying is that from now on I do not need to use the correct size drill as stated in the machinery handbook or on any tap/drill chart hanging on every machine shop wall across the globe, this will be some sad news for the drill manufacturers. DCoul could also have a depth issue but why in the hell would you not make the minor diameter of the tap the correct size?
    Bob Rice #6738
    He that conquereth his own soul is greater than he who taketh a city.

  5. #15
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    Quote Originally Posted by DCoul View Post
    reamer.jpg

    I see some that are like a real coarse drill bit and then there is this type. This type looks like it would work best if by hand. Sound right?
    Yes, in my opinion (I'm sure someone will disagree), a straight flutted reamer works best by hand. If it were me I would use a standard tap wrench holding onto the reamer diameter and run it through the holes using some type of cutting fluid. I still suggest a guide block to keep the reamer straight. Take your time, its your engine case. As I said previously, if you can test (duplicate) all this in a spare piece of aluminum it could prove all this out without spoiling the case. Good luck, I believe you have found the problem.
    Last edited by BigLakeBob; 10-24-2017 at 06:19 AM.
    Bob Rice #6738
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  6. #16
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    Great stuff, Bob. It's good to hear this stuff from someone who REALLY knows, instead of talking out their ass.
    Thanks for your input, I always pay attention when you speak.

  7. #17
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    Quote Originally Posted by BigLakeBob View Post
    I'm sorry Mr. Cotten but you are incorrect, taps do not size the minor diameter. I am aware they do make a drill/ tap combination for production work but we are not talking that here. Even if what you are saying could be remotely correct, which it isn't, if you read post #3 you will see he took the lead off of the tap. So what you are saying is that from now on I do not need to use the correct size drill as stated in the machinery handbook or on any tap/drill chart hanging on every machine shop wall across the globe, this will be some sad news for the drill manufacturers. DCoul could also have a depth issue but why in the hell would you not make the minor diameter of the tap the correct size?
    Please look at taps, Bob!

    Please note the lead-in taper that that relieves and finishes the inside diameter of the hole, if the pilot hole is proper, or under-sized.

    If your pilot drill is too big, it will indeed cut the inside diameter of the threads.

    This is pretty basic, Bob!
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    Last edited by T. Cotten; 10-24-2017 at 09:40 AM.
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  8. #18
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    Quote Originally Posted by T. Cotten View Post
    Please look at taps, Bob!

    Please note the lead-in taper that that relieves and finishes the inside diameter of the hole, if the pilot hole is proper, or under-sized.

    If your pilot drill is too big, it will indeed cut the inside diameter of the threads.

    This is pretty basic, Bob!
    Pretty basic is that what your arrows point to is the lead to cut the threads not the minor diameter. Just like a drill usually has a 118* or 135* point or lead cutting angle, flat bottom drills don't cut like ones with the standard points. They make taper taps, plug and bottom taps which each has their purpose. And of course if the drill cuts oversize it would cut the minor diameter, that is why there is a tolerance on minor diameters. A standard tap cuts the threads NOT the minor diameter. Well, this afternoon I have to drill and tap 104 1/4-20 holes in H13 mold steel, I probably won't use your suggestion in drilling undersize and letting the tap size the hole. Complete BS! I'm done discussing this with you. DCoul good luck and please post your results with your fixed engine case.
    Bob Rice #6738
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  9. #19
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    For those Folks who don't believe me,...

    Drill a deep hole with the prescribed drill for your tap size, then feel its slop in the hole.
    Then tap the hole, and inspect it again with the same bit.

    ....Cotten
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  10. #20
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    My tap didn't cut deep enough good to use the whole Helicoil insert. I then ground off the tip of the Helicoil so I could get it deeper in the hole which only bought me maybe another 1/8". I don't think I can get it deeper but I don't think I need to as it just holds the oil pumb to the bottom of the case with 4 1/4" bolts. I then cut a couple threads off the insert which worked on the first hole but not the next. My theory is, and this is a Helicoil rookie speaking here, that the tips of the threads in the tapped hole are too tall. I'll need to ream to take those off and re-tap. The depth of each thread is, I'm thinking, determined by the width of the tap, and since the hole is too small, the threads of the hole are too tall.
    I appreciate you guys helping with this. If I had paid closer attention to the package, I obviously wouldn't have screwed this up. It says in Bold letter 1/4-24, smaller lettering below: Drill Size/Diam.Trou/Tamano de la broca: 17/64 (.2656). Sometimes I get in a hurry.

    Details, details, details.

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