Results 1 to 17 of 17
  1. #1
    awake's Avatar
    awake is offline Stainless
    Join Date
    Jan 2006
    Location
    Angier, North Carolina
    Posts
    1,544

    Post

    This may be a dumb question, but I've never seen it addressed --

    I know that pipe threads are tapered. Could a person cut those threads on a lathe equipped with a taper attachment set to the appropriate taper?

  2. #2
    chips is offline Aluminum
    Join Date
    Oct 2002
    Location
    ohio usa
    Posts
    111

    Post

    YES, They can. It's sometimes easier to rough chase straight & run a die on though.

  3. #3
    lathefan's Avatar
    lathefan is offline Titanium
    Join Date
    Nov 2003
    Location
    Colorado
    Posts
    2,120

    Post

    Here's a boiler wash out plug being made without a taper attachment between offset centers:


  4. #4
    Jeff is offline Hot Rolled
    Join Date
    Jun 2001
    Location
    WI
    Posts
    656

    Post

    Yes. I tried it today on a SBL with taper attachment.

  5. #5
    gbent's Avatar
    gbent is offline Diamond
    Join Date
    Mar 2005
    Location
    Kansas
    Posts
    4,998

    Post

    I've done tapered threads by the ways listed above. The fastest way I have ever found on a manual lathe to chase them is with a tracer. That only works if you need to do a couple of dozen or more.

    The usual way I do them is to turn the tool upside down, and thread away from the chuck. Then I just turn the compound in as I feed off the part after I get the whole thread to the big end size. Do the math as to how much to feed in each revolution. With a little practice as to how fast to feed in, and you can pass a thread gage test.

  6. #6
    CatHead's Avatar
    CatHead is offline Hot Rolled
    Join Date
    May 2004
    Location
    Amherst, Nova Scotia , Canada
    Posts
    617

    Post

    The way I was shown, although dont know how many do it this way becuase there are faster ways, i guess, is to machine the taper(I believe its 1 degree and 47'?)then set your tool bit square with the diameter,NOT the taper you just cut...then thread away..

  7. #7
    SND
    SND is offline Diamond
    Join Date
    Jan 2003
    Location
    Canada
    Posts
    9,335

    Post

    On a lathe that doesn't have too much backlash and with some practice its possible to freehand the taper if the lathe doesn't have a taper attachment. Just cut the ouside taper with the compound first to have something to follow. It doesn't make a thread as accurate as if cut with a taper attachment. But sometimes it does the job if the pipe isn't running much pressure and that theres no chance for it to kill someone if it leaks. You can always chase it with a die after to fine tune it.

    At first I thought it was a crazy idea to freehand a pipe thread but after doing a couple I was quite pleased with the results. Although I wouldn't do it on anything critical or anything that was being sold to a customer. I'm just mentioning it because some guys just can't spend $1000 on a taper attachment to cut a thread for some widget they're making for the backyard.

  8. #8
    CatHead's Avatar
    CatHead is offline Hot Rolled
    Join Date
    May 2004
    Location
    Amherst, Nova Scotia , Canada
    Posts
    617

    Post

    does anyone do it the way I mentioned or am i way out in left field?

  9. #9
    tattoomike68 is offline Stainless
    Join Date
    Jan 2002
    Location
    home
    Posts
    1,028

    Post

    I do it just like gbent posted , its fast and works fine for pipe.

  10. #10
    SND
    SND is offline Diamond
    Join Date
    Jan 2003
    Location
    Canada
    Posts
    9,335

    Post

    CatHead, always set your tool square with the part. It's the way its supposed to be done. Never set the tool to the taper. So you're doing it right.

  11. #11
    JST's Avatar
    JST
    JST is offline Diamond
    Join Date
    Jun 2001
    Location
    St Louis
    Posts
    12,361

    Post

    That deal of setting square to the part is also how I was taught, and makes sense.

    It is also a really good argument for using a taper attachment.... You are setting square to the CENTERLINE of the part, which is actually at an angle if you are taper turning by offsetting T/S. Makes it hard to set to.

  12. #12
    olddude is offline Stainless
    Join Date
    May 2005
    Location
    JAPAN
    Posts
    1,225

    Post

    That's correct, don't set to the taper.

  13. #13
    willbird is offline Banned
    Join Date
    Jul 2005
    Location
    North(very) West(very) Ohio...near exit 13 on OH turnpike
    Posts
    3,714

    Post

    Also I read somehwere that for may pipe sizes it it acceptible to use a tapered female with a straight male thread, machineries handbook maybe ??

    Parts would not be to print so it would only be for parts you are making for your own use. I have used 1/8 NPS nipples before in a pinch and they worked fine with some teflon tape on them..that was before I read the information.

    Bill

  14. #14
    awake's Avatar
    awake is offline Stainless
    Join Date
    Jan 2006
    Location
    Angier, North Carolina
    Posts
    1,544

    Post

    I've got the taper attachment, assuming I ever get my lathe put back together! [img]smile.gif[/img]

    Do you taper the piece before threading, or just taper the threads themselves? And how much taper? Somewhere I think I read 1/4" per foot -- is that right, or did I dream that somewhere?

  15. #15
    Thermo1 is offline Senior Member
    Join Date
    Dec 2004
    Location
    Falls Church, VA
    Posts
    1,225

    Post

    With regard to mixing straight and tapered threads, the following may be helpful:
    "Pressure tight joints for low pressure servce are sometimes made with straight internal threads and the Americian Standard taper external threads. The ductility of the coupling enables the straight threads to conform to the taper of the pipe thread. In commercial practice straight-tapped couplings are furnished for standard-weight (Schedule 40) pipe sizes 2" and smaller."

    pg 7-150, Piping Handbook, 5 ed, McGraw Hill. Chapter 7 was written by Helmult Theilsch, manager of the Research and Development Division, Grinell Corp, and one of the recognized authorities on piping. In many ways the 5th edition of this handbook is better than the 6th edition.

    Oh, Yes, the taper is 3/4 inch per foot.

    Thermo1

  16. #16
    Scott R is offline Hot Rolled
    Join Date
    Jul 2005
    Location
    NE Ohio
    Posts
    517

    Post

    You dont have to taper the work piece before threading. The threads will be tapered

  17. #17
    Peter S is offline Diamond
    Join Date
    May 2002
    Location
    Auckland, New Zealand
    Posts
    4,023

    Post

    Is it possible to do this properly by off-setting the tailstock? I am worried about that boiler washout plug now ... Not something to get "roughly right".

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •