1” BSP Tap in the lathe

  1. Brad93

    Brad93 M J B Engineering

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    Location:
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    I’ve just tried to tap a 1” BSP thread in a piece of 50mm round bar (mild steel).

    I’ve got a Second tap, Presto, brand new.

    Bored out to 30.73mm 0.02mm under what the Zeus book says, thought that will be alright.

    got the tap about 6mm in and it is just solid.
    Got a 12” bahco on it!

    Took another 0.6mm out of the bore. Still mega tight managed to get about 10-12mm of threads in, just enough for the taper plug I want to use, to seal.

    What have I done wrong?
     
  2. Seadog

    Seadog Forum Supporter

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    6,970
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    NE London - UK
    The Zeus chart is for BSPP I believe, so should be oversized if you're using a BSPT tap. Better lube needed, perhaps?
     
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  3. brightspark

    brightspark Member

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    I had same with a half inch bsp tap from zeus book, just bored it out a touch more till it threaded ok
     
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  4. Brad93

    Brad93 M J B Engineering

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    I’m using a BSPP tap as far as I know. Two minutes I’ll double check.
     
  5. jimi_boom Member

    Messages:
    103
    LAncaster
    I don't use the Zeus book I prefer the engineers reference pocket book and that has the tapping drill size as 30.75mm and that is for a BSPP
     
  6. Brad93

    Brad93 M J B Engineering

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    Location:
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    That’s what the Zeus book says too
     
  7. Brad93

    Brad93 M J B Engineering

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    Just standard BSP?
     
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  8. Brad93

    Brad93 M J B Engineering

    Messages:
    10,386
    Location:
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    1mm over size (31.72) and still won’t cut any deeper. Calling it a day.
     
  9. Brad93

    Brad93 M J B Engineering

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  10. brightspark

    brightspark Member

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    all I did was get a half inch bsp threaded coupling and took the bore measurement from it and used that to measure and it worked and threaded fine
     
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  11. 8ob

    8ob Forum Supporter

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    moscow on thames
    Do you want to borrow a bspt tap ?

    Bob
     
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  12. Matchless

    Matchless I started with nothing, still have most of it left

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    man after my own heart, drop a drill through a nut, tapping size...…..:whistle:
     
  13. Guzrik Member

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    182
    Location:
    Holland Noord Brabant
    Never saw that book, looks interesting.
    I always use https://www.gewinde-normen.de/whitworth-rohrgewinde.html but that says 30,292mm so incorrect I would say.
    If it doesn''t have to hold a thousand bar I wouldn't bother and cut another half a mm out.
    I sometimes try to get some speed and heat into the chips so they bend easier into curls, but with these sizes that takes a lot of power.
     
  14. Kram

    Kram Member

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    1,781
    Location:
    Sussex
    It is a big tap, needs bigger extension, like 600mm or single point it.
     
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  15. mike os

    mike os just a little insane.....

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    Second cut is hard work when its that big....
     
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  16. brightspark

    brightspark Member

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    31,687
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    a flamin half inch one is bad enough I started in the lathe so its parallel then transferred to the vice and used a big adjustable spanner and that's hard work its bad enough threading 25 mm conduit with large handle dies
     
  17. Brad93

    Brad93 M J B Engineering

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    Location:
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    Well then, that’ll be what it is. Will get making a big tap handle and finish tapping it in the vice.
     
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  18. mike os

    mike os just a little insane.....

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    6,963
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    At least a 600mm one
     
  19. rory1

    rory1 Member

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    There will be a few machine tool lovers on here that won’t like this, but hey ho - I’d get it started with a centre in the back of the tap and a shifter against the bed and then either turn the chuck using the key or put it in a low gear and give it some power
     
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  20. brightspark

    brightspark Member

    Messages:
    31,687
    Location:
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    the stress is that much on the chuck the job just turns. the pressure will stall the motor even in backgear you wouldnt get quarter of the pressure needed using the chuck key as the lever
     
    mike os likes this.
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