Fettling a roarer burner with broken nipple/stripped threads. Part 1 - without cutting the tubes

Discussion in 'Fettling Forum' started by Twoberth, Jul 2, 2020.

  1. Twoberth

    Twoberth United Kingdom Subscriber

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    I have several roarer burners with broken off nipples, or with stripped threads. This documents my attempt to repair without cutting off the tubes.

    I have already documented how to make oversize nipples at the bottom of this post here, so this technique can be used whether re-threading with a homemade oversize tap and nipple, or removing a broken piece, and using a replacement regular nipple.

    Rethreading
    First, turn a thread into an old 5mm drill bit shank (0.5mm pitch) to make the oversize tap

    2020-06-29 001 008.JPG

    and cut off a 2cm piece and cut flats to fit the nipple removal tool. Then, using an old/broken 4.5mm drill bit, cut about 2cm off the fluted end and sharpen one end to 130 degrees, and file flats in the other end to fit a nipple removal tool.

    2020-06-29 001 009.JPG 2020-06-29 001 010.JPG 2020-06-29 001 011.JPG 2020-06-29 001 012.JPG 2020-06-29 001 013.JPG

    Cut the remains of the stripped thread out with the drill bit,

    2020-06-29 001 018.JPG 2020-06-29 001 021.JPG 2020-06-29 001 016.JPG

    and then re-cut a new thread with the oversize tap.

    2020-06-29 001 019.JPG

    You then need to make and fit oversize jets as detailed in the link above.

    Removing broken nipple thread

    This is the same technique, but with a homemade flat screwdriver-type bit to 'bite' into the broken thread. You can use the normal nipple removal tool, but I have had more success using the tool shown, and levering pressure onto the top of the tool from above while turning.

    2020-07-02 001 015.JPG 2020-07-02 001 016.JPG

    In my experience..

    a) the drill and rethreading tools work fine, and the removal tool not so good.
    b) both take a long time to make the bits, and to effect the repair.

    If you are not confident with brazing and are reluctant to cut off the tubes, this may be your best chance at a repair.

    However if you are confident you can re-braze the tubes, cut through two of them to remove the bend with the nipple seat. This gives you full access to the nipple hole and is by far the easiest repair, as shown in Part 2.
     

    Attached Files:

  2. Murray

    Murray Subscriber

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    Amazing - the mystery of using the short Primus taps solved. No flutes or hardening required on the tap - I guess it picks up the damaged thread and forces the brass into shape rather than cutting a new thread?
    Bravo!
     
  3. Twoberth

    Twoberth United Kingdom Subscriber

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    @Murray
    I didn't know about the short taps until recently, then the penny dropped.

    I initially tried fluting the taps, but it seemed to make no difference. HSS drill bit shanks are soft enough to thread, and hard enough to form the thread. There is some swarf produced when threading but I suspect you are correct, it is more of a pressed thread profile than a cut profile
     
  4. ROBBO55

    ROBBO55 Subscriber

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  5. Tantra

    Tantra Subscriber

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    Yes I have found same problem