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Old 09-18-2009, 10:53 PM
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Question about re-tapping

I have a 1.25"ID titanium tube with 24tpi threads. Can I just retap it to 12tpi? I want it the same diameter just want it from 24tpi to 12 tpi

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Old 09-18-2009, 11:59 PM
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Won't work. If its currently tapped 1.25-24 then the hole is too big to tap for 12tpi and get a thread with any strength.

The tap drill size, or hole size is equal to the major diameter minus the thread pitch. For a 1.25-24 that would be 1.25 minus .042 = 1.208"

For 1.25-12, the hole size should be 1.25 minus .084 = 1.166"

If you were trying to go the other way, you could drill or bore it out to the larger hole size and retap. That would work fine since the threads are even multiples of each other. But to go from 24 to 12 in the same hole won't do anything but mess up your existing thread.
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Old 11-04-2009, 07:33 AM
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agreed that it wont work. it is considered bad practice to cut one thread over another. It can be done in some situations but as was stated earlier, not this one. As an aside, the 24 TPI is stronger than the 12. why not get the right mating thread and not mess up your titanium tubing?
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Old 11-05-2009, 08:54 AM
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Our two learned colleagues preceedeing me are correct.

Another consideration, were this feasible, would be the cost involved. You aren't likely to find or afford a drill and tap to do this. It would have to be done on a lathe with inserted tooling. Also rather spendy.

I'm guessing this might be a bicycle part. If so, it might be better to have a different one made by a local shop experienced in internal threading of Ti. I'm guessing a couple hundred dollars.
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