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Thread: 27mm 1.25 Pitch Tap

  1. #1
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    Jughead's Tools

    27mm 1.25 Pitch Tap

    I repair motorcycles for a living, and recently has to remove a gearbox from a BMW R1150GS. The swingarm, which houses the driveshaft, pivots inside the aluminium gearbox casing. Unfortunately, whilst removing the pivots, one of them went threadbound and ripped the thread in the casing.

    This necessitated making a 27mm 1.25Pitch tap, and a jig to make sure the repair was straight and inline with the opposite side. I started off with a 30mm piece of EN36.
    27mm 1.25 Pitch Tap-20240910_165313.jpg

    Added some marking dye
    27mm 1.25 Pitch Tap-20240910_163333.jpg

    And single pointed a 1.25mm pitch thread.
    27mm 1.25 Pitch Tap-20240910_170933.jpg
    27mm 1.25 Pitch Tap-20240910_172008.jpg

    Drilled and reamed a 12mm hole down the center
    27mm 1.25 Pitch Tap-20240911_085541.jpg

    Then took it over to the milling machine for a few flutes.
    27mm 1.25 Pitch Tap-20240911_100752.jpg

    8 in total
    27mm 1.25 Pitch Tap-20240911_102233.jpg

    Then flipped it over to cut a square on the back end
    27mm 1.25 Pitch Tap-20240911_105110.jpg

    Done
    27mm 1.25 Pitch Tap-20240911_105617.jpg

    Looks a bit messy after the heat treat, but nothing a scotchbright wheel cannot solve
    27mm 1.25 Pitch Tap-20240911_111714.jpg

    Then made a small guide adapter for the opposite side from and old buggered pivot
    27mm 1.25 Pitch Tap-20240911_114112.jpg

    And finished of with a 12mm stainless guide shaft.
    27mm 1.25 Pitch Tap-20240911_114057.jpg

    So it works like this
    The guide adapter screws into the LHS pivot hole and accommodates one end of the 12mm shaft
    27mm 1.25 Pitch Tap-20240911_114546.jpg

    The newly made tap slides on the guide rod and is used backwards and exits the hole on the RHS, repairing the thread as it goes. This ensures that the thread is exactly in line and there is no chance of cross threading it, which is very easy with such a large (26mm) tap.
    27mm 1.25 Pitch Tap-20240911_114542.jpg

    27mm 1.25 Pitch Tap-20240911_114602.jpg

    27mm 1.25 Pitch Tap-20240911_114637.jpg

    And with a little black added.
    27mm 1.25 Pitch Tap-20240911_152135.jpg
    Download plans for drilling and drill presses.
    Last edited by Jughead; Sep 11, 2024 at 09:12 AM.

  2. The Following 7 Users Say Thank You to Jughead For This Useful Post:

    BuffaloJohn (Sep 12, 2024), DIYer (Sep 12, 2024), Frank S (Sep 11, 2024), Jon (Sep 11, 2024), mr mikey (Sep 12, 2024), olderdan (Sep 11, 2024), wood_1 (Sep 12, 2024)

  3. #2
    Supporting Member olderdan's Avatar
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    Nice fix, I had to do similar for the exhaust ports of my veteral AJS.
    Download plans for drilling and drill presses.

  4. The Following User Says Thank You to olderdan For This Useful Post:

    Jughead (Sep 13, 2024)

  5. #3
    Supporting Member Frank S's Avatar
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    A hollow tap with internal guiding rod is a rarity indeed and a unique way to insure you started straight in the original undamaged part of the thread.
    Not saying they don't exist, but I don't think I've ever seen one other than line taps for tubing fittings
    Last edited by Frank S; Sep 11, 2024 at 05:47 PM.
    Never try to tell me it can't be done
    When I have to paint I use KBS products

  6. The Following User Says Thank You to Frank S For This Useful Post:

    Jughead (Sep 16, 2024)

  7. #4
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    Thanks Jughead! We've added your Tap to our Tapping and Threading category,
    as well as to your builder page: Jughead's Homemade Tools. Your receipt:

    tags: tapping



  8. The Following User Says Thank You to DIYer For This Useful Post:

    Jughead (Sep 16, 2024)

  9. #5
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    I have worked on a lot of different types of machinery in my life lifetime. Everything from air conditioning to Nuclear power plants on Navy surface ships and submarines to gas turbine powered generators and cogeneration plants as a civilian, and there have been countless times a tap like that would have been a dream!
    I'm almost ready to retire now and I think that i just might have to try making some of those for m y sons who are in the trades.


    Download plans for drilling and drill presses.

  10. The Following User Says Thank You to motorhead For This Useful Post:

    Jughead (Sep 13, 2024)

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