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Re-tapping a thread - question

  • 02-03-2019 9:43pm
    #1
    Pops_20
    Registered Users, Registered Users 2 Posts: 725 ✭✭✭


    When fitting a seat belt buckle to a seat rail today I unfortunately cross threaded the bolt and stripped the thread on the nut which is welded to the rail.

    The bolt was slightly damaged but I test fitted it to another nut and it seems that it will be re-usable.

    However the nut is too far gone and it looks like I will have to either re-tap the thread or else cut off the nut (welded to the frame) and then use a new bolt and nut.

    My question is, can you re-tap a thread that has been damaged with the same size thread, or does it need to be a larger size?

    In this case the thread I believe is 7/16" UNF -20.

    Hoping some of the more knowledgeable posters on here can help as I have never damaged something this badly when working on cars :o


Comments

  • #2
    w211
    Closed Accounts Posts: 416 ✭✭w211


    Use the thread chaser or if you have a same size extra bolt, make a own thread chaser by cutting the slot(s) to the bolt thread. Re-threading are not the good option because the thread cutter will remove too much extra material and it may not hold anymore properly.


  • #3
    DublinDilbert
    Registered Users, Registered Users 2 Posts: 5,421 ✭✭✭DublinDilbert


    Depends how badly it was damaged, if you can get a tap to run in the same thread you might be ok. The proper job is to drill out and use a heli coil.


  • #4
    Pops_20
    Registered Users, Registered Users 2 Posts: 725 ✭✭✭Pops_20


    DublinDilbert wrote: »
    Depends how badly it was damaged, if you can get a tap to run in the same thread you might be ok. The proper job is to drill out and use a heli coil.

    Thanks, it's hard to tell how badly damaged it is as its inside the nut itself and had to see, but it seems pretty knackered.

    Are helicoils safe for a component such as a seat belt buckle? I understand they are like slotting a new thread into the same place, as opposed to cutting away the metal with a tap. I will need to do some research.

    Will a tap of the same size "catch" on some of the same old threads, or will it create all new ones?


  • #5
    Pops_20
    Registered Users, Registered Users 2 Posts: 725 ✭✭✭Pops_20


    w211 wrote: »
    Use the thread chaser or if you have a same size extra bolt, make a own thread chaser by cutting the slot(s) to the bolt thread. Re-threading are not the good option because the thread cutter will remove too much extra material and it may not hold anymore properly.

    Do you mean cut a notch into the bottom of the bolt? Or cut into the threads itself? I wouldn't be too confident with this.


  • #6
    w211
    Closed Accounts Posts: 416 ✭✭w211


    Pops_20 wrote: »
    Do you mean cut a notch into the bottom of the bolt? Or cut into the threads itself? I wouldn't be too confident with this.
    2 slots(opposite side), cross the thread from the beginning and so long as you need.
    The slot can be bit wider than normal dremel disk thickness (cuts 2 times the single slot). It must only little deeper than thread. Works ok for DIY thread chaser and cost for you only 1 bolt. If the thread are completely destroyed, then even the proper thread chaser can not fix it. Little wd40 can helps to make the thread chaser smooth.


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