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BSPT thread ? What angle???

RABISON

Plastic
Joined
Feb 17, 2006
Location
UK
Hope u guys can explain this to me. I dont come across these BSPT threads much, once in a bluemoon.The other day I had to m/c 10 off tubes that called for a 2.5"BSPTx25mm long thread on 1 end, and for the life of me (and my boss by the way)couldn't figure out how u work out what taper to machine on the od, as after looking up in the machinerys handbook it states "thread od 2.960 depth 0.058 taper is one in 16". ????????? how do i work out what my od would be at small end of thread? What am i missing :(
 
I've been going through my Machinery Handbook but it is the 1941 Edition. We Geordies are mean, real mean.

Somehow, you may have the straight and tapered details mixed up- or I have to get a new(er) Machinery Handbook. Try the "Copper" variety in BSPT

Cheers

Norm
 
The OD for the straight is or was 2.960 and 11 TPI but the max od for the taper is 2.684 to 2.599 and 16 TPI.

Mind you, the Yanks had doubts whether we would win the War when my copy was sent. You will note the disparity- which is why I raised the question.
To Fool the Bosch?

Regards

Norman
 
From what I have observed, British Standard Tapered Pipe Threads are similar to American threads, except where noted otherwise. The taper seems to be the same, 1 in 16, or 3/4" to the foot, and the dimensions are pretty close, but in places the number of threads per inch (US) or thread pitch (UK) are different. US uses 11 1/2 tpi, UK uses 11. Machinery's Handbook does have the dimensions, but make sure you use the table for the right country, or you will be close, but not quite!

Thermo1
 
..but the Whitworth tools provide a MUCH nicer product!

I just can't get over using ONE guage to check pipe threads. I generally use three!


Think Snow Eh!
Ox
 
I have at least three cnc`s making BSPT pipe fittings continuously.As stated the taper is 1 in 16 but the hard bit is measuring it as the gauge line is not at the end of the taper.Stellram have a lot of good info on their site,including a programme which will give you the turning dimensions for the taper,
BTW Thermo it`s not just the Brits that use BSP.It was adopted as the standard ISO pipe thread.
regards,Mark.
 
thanx for the replys people, tho maybe i didnt explain myself correctly. I know that the thread included angle is 55*, it is the 1 in 16 taper i dont understand i.e if 2.5 BSPT thread nominal od is 2.960" how do u work out the od of the small end of the taper at the start of thread. thanx again.
:rolleyes:
 
Mark,
To take this thread in just a slightly different direction, are the British Standard pipe sizes the same as the American ones? In the thread standards they look pretty close.

If the British Standard is now the ISO standard, are the ISO standard pipe sizes the same as the British ones?

Thermo1
 
Rabison,

I have no experience in cutting tapered threads...

I am guessing the 1 in 16 taper is the included angle?

If so, I worked out the taper on a triangle of 0.5 in 16, this gives 1 deg 47 minutes (or 1.79deg), so this is what you would set your compound slide to....I think!

Or...if your OD is 2.960" and thread length 25mm, then the "small" dia will be 2.898".

Am I on the right track?

Further.....you know some clever dick is always giving the answer you don't want....its me this time!


I would take them to someone who has a powered threading machine, they will make short work of your threads.

Commonly found at anyone who sells pipe and fittings. Inexpensive task, they use tangential type cutters that put the taper and thread on in seconds.
 
The major diameter given for a BSPT thread is at the gauge line,so the big end of the taper is bigger to so that there is a wrenching allowance for tightening.
Thermo,yes the ISO pipe threads are the same but there are one or two variations within the standard.Mainly to do with how it is gauged.
ISO 2"R is a 2" BSPT,ISO 2" Rp is a 2" BSP is a parallel internal thread but it is checked with a taper gauge.G2" is bog standard BSP.
I`m not sure about NPT as we don`t often do them.
I will look into it.
regards,Mark.
 
rabison
Peter S is correct the angle is 1deg 47mins and the nominal dia is taken at the gauging line as Mark McGrath states.
the small end of your thread = Nominal dia -(gauge length * taper)this is the basic size with no allowances
example 2.50-(.6875*.0625)=2.457, the gauge length can be found in 'Machinery Handbook', i have the twentieth edition and they are on page 1404, for 2.5" the gauge length is 7 9/16 (7.5625) you have to multiply this by your pitch hope this helps
 
Thanks for all the replys people, LBMAKEM mate u have hit the nail on the head mate !!!
u have explained the answer i was looking for very well, excactly what i was asking! just need to put it into practice now ,thanks again. I dont post much but i love this site ,learning more every time i log on.
 
Mark,
The British Tapered Pipe Thread table in Machinery's Handbook shows the major diameter almost exactly 0.050" smaller than the OD of US standard pipe, which is why I wondered,

Thanks,

Thermo1
 
Thermo,it`s because as discussed the thread major diameter is measured down a bit from the large end of the thread.When you gauge a BSPT thread,the gauge should be hand tight at the gauge line but there should still be 4-5 threads behind the gauge for the fitting to tighten on so it follows that the pipe od must be bigger than the major diameter of the thread.
Is NPT not measured the same way?
We were actually supposed to be running some NPT fittings this week but the customer only had one gauge which they were using so decided to do the job themselves.Pity as it would have let me compare the actual differences between BSPT and NPT.
regards,Mark.
 
Mark,
Thanks a lot, this begins to answer a question I have had for a long time: What pipe sizes are used in Europe?

NPT sizes give the pipe OD, and a lot of measurement points, most of which are down on the threads. I suppose I should get out my copy of Machinery's Handbook and check the thread sizes, now that I know where the British threads are measured.

It sure looks like ISO sizes are pretty close to US standard pipe sized, only converted to metric.

Thanks for the information, I will do some checking on my own, but I may get back in touch via another thread.

Thermo1
 
Hi Mark ! nice to meet a fellow scot on here ,small world eh? I,m from just outside Glasgow in a small green and white town called Coatbridge haha . What about yourself?
 








 
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