How To Define A BSP Male Taper Thread on a Drawing

[anyoldname]

I'm drawing up a custom fitting that requires a 3/4 BSP tapered male thread on one end of it.

I have a copy of BS21 (1995) which defines how a taper thread is defined with gauging diameters and planes etc.

My question is whether this is necessary on the manufacturing drawing. There must have been many thousand drawings of such threads created over the years and I can't quite believe that ever BSP/NPT/whatever taper thread was defined in such detail. Is there a standard convention used to show such a thread on a drawing? eg For an M6 hole, you can just use a note saying M6x1 (6H)

When the part is being made, the length of thread will be constrained by the the base diameter of the material and the cutting die. The die will only cut so far onto the basic diameter of the material before both the major and minor diameters are cutting/touching the outer diameter. I know from experience with taper taps that its very obvious when this condition is reached and you have a fully formed thread. To turn it any further would:
-A: Require big muscles.
-B: Probably break the tap.

Hope someone can advise me on this.

Thanks in advance, AJ

 

[ornerynorsk]

There are go/no go gauges for this, as well as other pipe threads. It is understood that the thread must be within gauge limits. You could note as such on the drawing, rather than writing a discourse of numerical dimensions.

 

[desertfox]

Hi anyoldname

Look at this site:-

http://en.wikipedia.org/wiki/British_standard_pipe_thread

BSPT threads are designated with an "R" where just BSP threads are designated with a "G"

desertfox

 

[hydtools]

You will not know if your process is under control if you do not inspect to verify that the thread meets the standard. You must specify the standard or imply the standard, yet expect to inspect and verify the thread.

If you are a one-off shop, you make the part and you just know when the thread is correct then why worry about the standard? Unless your cusotmer cares. Or the shop that will make your part cares to provide a part which will work the way you intend.

Ted

 

[JLSeagull]

For me to understand, you could include a note on the drawing requiring the BSP Male Taper Thread.

 

[ione]

Pipe threads are formally referred to by the following sequence of blocks:

• the words "Pipe thread",

• the document number of the standard

• the symbol for the pipe thread type:

o G = external+internal parallel (ISO 228)

o R = external taper (ISO 7)

o Rp = internal parallel (ISO 7)

o Rc = internal taper (ISO 7)

• the thread size

 

[desertfox]

Hi anyoldname

Have look at this catalogue on page 20 its gives the length of thread on the fittings.
I have never specified a length of thread when calling up BSPT threads just the size like R3/8"

desertfox

http://www.valinonline.com/images/support_docs/Parker_4260_pipeftg.pdf

 

[eadwine]

anyoldname,

What we've always done with odd or non-spec threads, is use a local note with an arrow pointing to the thread location.

In your case,

3/4" BSPT ---------->

or

3/4" NPT ------------>

or

"Whatever" ------------>

Get the picture? Fabrication, Installers, and Maintenance will then reference the proper thr'd. spec. (hopefully).