Tap drill for 3/8-28 tap - Page 2
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  1. #21
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    Reduction from nominal to tap hole size is consistent across thread pitches, assuming they're of like form.


    Barring the book, just check the delta on a 1/4-28.

    Sent via CNC 88HS

  2. #22
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    Quote Originally Posted by plastikdreams View Post
    1/8 bsp straight.
    So 1/8 BSPP?

    Sent via CNC 88HS

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    Quote Originally Posted by triumph406 View Post
    and to cap it all a machinist who can't figure out the right diameter drill for a tap........
    Pretty much...that's why I asked. And if you actually READ my op I had an answer I was just double checking.

    Quote Originally Posted by Cole2534 View Post
    So 1/8 BSPP?

    Sent via CNC 88HS
    Sure lol like I said I have 0 experience with bsp

  4. #24
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    For sng here's picture from my mh for tap drill sizes for American thread forms

    20210307_092834.jpg

  5. #25
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    Quote Originally Posted by plastikdreams View Post

    Sure lol like I said I have 0 experience with bsp
    I recalled that there were specs for BSP and BSPP - British Standard Pipe and British Standard Parallel Pipe. The first tapered as US pipe threads and the other not, so it's worth knowing more specifically what's called for.

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    Quote Originally Posted by TGTool View Post
    I recalled that there were specs for BSP and BSPP - British Standard Pipe and British Standard Parallel Pipe. The first tapered as US pipe threads and the other not, so it's worth knowing more specifically what's called for.
    The one engineers reply was, if it's too lose we'll use Teflon tape...it's out of my hands now.

  7. #27
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    My tap drill calculator will do 55 degree threads. Or any other angle.



    Quote Originally Posted by gustafson View Post
    And 55 degree thread.....of course all of our first questions should be 'why' rather than just rushing for the solution

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    British Standard Pipe - Wikipedia

    G specifies parallel threads
    R denotes tapered threads

    WTH is going on in the UK?

  9. #29
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    Us does the same with pipe threads. NPT are tapered. Conduit threads are straight.
    Bill D

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    But why G and R?

    Maybe derived from French words when they made it an ISO standard?

  11. #31
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    Quote Originally Posted by Bill D View Post
    Us does the same with pipe threads. NPT are tapered. Conduit threads are straight.
    Bill D
    There are some straight threads used in large hydraulic stuff, usually using a copper washer in the bottom to seal.
    JH

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    I haven't tapped 3/8-28 but have tapped 3/8-24. I used a Q drill for 75%. I would think the R drill would be fine. Also the formula as stated by at least two others say that major diameter ( 3/8 ) minus the pitch 1/28
    is a correct formula for a tapped hole. .375-.028 = .347

  13. #33
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    Quote Originally Posted by Bill D View Post
    Us does the same with pipe threads. NPT are tapered. Conduit threads are straight.
    Bill D
    no, rigid conduit uses NPT tapered threads, when was the last time you threaded some together?

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    Quote Originally Posted by plastikdreams View Post
    Sure lol like I said I have 0 experience with bsp
    Here's a handy site for most things thread related.
    This page has all the info on BSPP threads.
    Thread Data Charts

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    Quote Originally Posted by plastikdreams View Post
    Bsp wasn't even remotely in the equation...I've never even threaded anything bsp. Funny thing is, they brought me 2 taps and a similar part that would thread into the block. The nut on the part threaded onto the 3/8-28 a little loose but wouldn't even start on the bsp tap. Tapped a hole using the 3/8 tap and the part was very tight threading in, tapped a hole bsp and the part was just a little lose and the nut could be used to tighten it up. Crazyness...
    When stuff like that happens around here its typically because someone is "reverse engineering" (aka copying) something. then of course all the tolerances get tightened up to .001" because they have no idea what it really needs to be in order to work. So instead of actually engineering something and using a calculator they do whats easiest for themselves.....tighten it uo to make it exactly like the one being copied.....i mean reverse engineered,,,lol

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    Quote Originally Posted by plastikdreams View Post
    I didn't see 28 in my mh v28. But looks like the numbers match up. Looks like they are going to use a nut to tighten up some threaded suction cups to hold vacuum. I guess npt wasn't good enough
    May I make a Wild Ass Guess here?

    You're making a mating piece for a Festo push-in type fitting!

    If I was correct and won, then let me go for bonus points!

    You might be making a part for a FESTO BSPT(R/Rp) style combo, in which case your female thread is a BSPP, while the male thread is BSPT
    IOW, as-per FESTO specs, they want a 1/8-28 British tapered male fitting to fit into a 1/8-28 British straight hole.

    ( 'About to make the very same threads into some tubing, also for vacuum application on a German machine. )

  17. #37
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    Quote Originally Posted by SeymourDumore View Post
    May I make a Wild Ass Guess here?

    You're making a mating piece for a Festo push-in type fitting!

    If I was correct and won, then let me go for bonus points!

    You might be making a part for a FESTO BSPT(R/Rp) style combo, in which case your female thread is a BSPP, while the male thread is BSPT
    IOW, as-per FESTO specs, they want a 1/8-28 British tapered male fitting to fit into a 1/8-28 British straight hole.

    ( 'About to make the very same threads into some tubing, also for vacuum application on a German machine. )
    Nah it's some kind of thread in suction cup.

  18. #38
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    The key thing is this is not really a load-bearing threaded hole. So, make it easy on yourself and use a larger drill for a 65% thread. There is not need whatsoever for a 75% thread in this application.

    Denis

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    I'll never know if it works, but I know I will if it doesn't

  20. #40
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    Quote Originally Posted by plastikdreams View Post
    Nah it's some kind of thread in suction cup.
    Well, that does not exclude Festo from the list of culprits: Buy Vacuum suction cup VAS, VASB online | Festo USA


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