Geometric threading npt
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  1. #1
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    Default Geometric threading npt

    When using the geo head and threading npt
    Threads do I need to taper stock 1st or run the head loose then finish sorry if this was already posted

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    Quote Originally Posted by Cruiser1 View Post
    When using the geo head and threading npt
    Threads do I need to taper stock 1st or run the head loose then finish sorry if this was already posted
    The stock should be tapered first to, I think, 3/4 in per foot and then threaded for male threads. For female threads, it is best to taper the bore with a specific tapered reamer first before tapping. Many do not ream first, but it increases tap load appreciably which can hurt the thread quality.

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    Quote Originally Posted by steve-l View Post
    The stock should be tapered first to, I think, 3/4 in per foot and then threaded for male threads. For female threads, it is best to taper the bore with a specific tapered reamer first before tapping. Many do not ream first, but it increases tap load appreciably which can hurt the thread quality.
    You should always taper first. Free cutting brass you can get away with it but why would you want to. It doesn't help the chasers,the diebox or the tap, you are just storing up problems for later.

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    My understanding is that threading tapered threads on straight material, either male or female is NPT. Tapering the material, male or female is NPTF, or dryseal pipe threads. In my industry we used NPTF exclusively. Since we never made male fittings, our female NPTF threading always involved taper reamers.

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    If you do not want to pre taper the part a ridgid die head in a pipe machine does a great job. Best for pipe though, not precision.

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    Quote Originally Posted by R. Dan View Post
    My understanding is that threading tapered threads on straight material, either male or female is NPT. Tapering the material, male or female is NPTF, or dryseal pipe threads. In my industry we used NPTF exclusively. Since we never made male fittings, our female NPTF threading always involved taper reamers.
    No. They are both tapered. NPTF and NPT threads are very nearly the same. The difference is that assembled NPT threads make full contact only along the thread flanks, which can leave a bit of a gap along the root/crest where the threads mate, so NPT needs a sealant or pipe tape to insure that the gap is definitely blocked. NPTF threads are dimensioned ever so slightly differently so that they make contact on the flanks and the root/crest simultaneously so they should seal better even dry (hence the "dryseal" moniker).

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    Thanks - cruiser1


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