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    Default BSP Thread data

    Hi All,
    Does anyone have the details for 1 7/8 BSP thread please, I have looked on the net and can only find 1 3/4 and 2".
    Kind Regards
    Steve

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    The books I have all show the same as what you have found for BSPP or BSPT. No 1 7/8.

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    Hi,

    Are you sure it is 1 7/8" BSP ? 1 1/2" bsp is 1.882" outside diameter and tube is usually 1.875" plus or minus 0.010"

    Buchanman.

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    Is this on hydraulics ? 1 7/8BSP is an oddball and hyd's are the only place I've come across it.

    You will have to work back from the published formula for 11TPI BSP

    PS Good point Buchanman

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    Hi guys,
    Thanks for the replys, It is 1 7/8 x 11 BSP but I cant find the details for screwcutting it, I have managed to source a Tap for the nut but I will have to screwcut the body. I will have to measure the major diamiter when the tap arrives.
    I am making a batch of steam injectors (These were last produced about 60 years ago) and the age probably explains the odd size threads I have found on the pattern injector.
    Kind regards
    Steve

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    Quote Originally Posted by feet n inches View Post
    (These were last produced about 60 years ago)
    The first place I looked was my 7th edition "American Machinists Handbook", but nothing!

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    Steve

    Found it! Listed under Original Whitworth Pipe Thread in "Guide To World Screw Threads" by P.Sidders, mine is 20 th British Edition copyright 1969 but clearly printed a lot later.

    Data:- 11 TPI, Pitch 0.09091, Depth 0.0582, Major Diameter 2.2450, Effective Diameter 2.1868, Minor Diameter 2.1286. Far as I can see its standard 11 TPI BSP / constant pitch Whitworth sizing.

    Gawd knows what the tolerances and allowances are supposed to be. I guess using figures for nearest 11 TPI BSP will be good enough, or maybe those for hydraulic pipe threads would be better. My book lists both if you need (and can understand) them.

    Certainly obscure, none of the general engineers handbooks I have list it, 3 Editions of Machinerys, Newnes, Caxton, and a couple of others plus info embedded in other sources. Wonder if Molesworth had it! Surprising as some of the other stuff listed is seriously more obscure, especially given the following quote from "Guide to World Screw Threads".

    "Important Note: For certain intermediate sizes of pipe thread in was the practice of the engineering trade to adhere to the dimensions of the Original Whitworth Pipe threads for which there exists no official standards."

    Clive
    Last edited by Clive603; 05-02-2012 at 04:32 PM. Reason: Added quote and notes thereof.

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    Well done that man:-)

    I'd half wondered if it was an old Whitworth Pipe Thread size,..... I drew a blank with all my old books.

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    The curious thing about BSP is that it's effectively defined for larger sizes than Whitworth or BSF. I've got drawings for a diesel engine where a camshaft nut is specced at 3.5" BSP==3.5" 11tpi

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    It's often used for large non standard fastenings, I think, on account of it's fine rate for diameter and easily interpreted international standard.

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    Hi Clive,
    Excellent bit of detective work, cant thank you enough. The tolerances are not a major issue as i will make a dummy gauge, its only for a stuffing gland. When I was taking all the dimentions off the original injector I found the thread listed online but I failed to find it again when I needed the full details. The other threads on it were 1 1/8 x 11 BSP and 1 5/8 x 14 UNS.
    The next fun bit is to make a tapered reamer for the valve chamber.
    Kind Regards
    Steve

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    Quote Originally Posted by feet n inches View Post
    The next fun bit is to make a tapered reamer for the valve chamber. Steve
    In case you don't know Tapered D bits made out of Silver Steel (drill rod) work well in most non ferrous - just don't rush them - though I've never gone higher than about 7/16'' at the small end I can't see why they shouldn't work.

    Has this big injector got seperate / loose cones in a body?

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    The taper is 1.1 inches at the small end and 1.65 at the large end so I have opted to modify a No12 brown and sharp taper reamer, Its quite a bit of work but should work well.
    It has three fixed cones and a "spinner" cone in the center (overflow chamber), the biggest challenge is to get the clearances correct! Have you had much experience with steam injectors?
    Regards
    Steve

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    Played with injectors and water lifters a bit, but they were much smaller than that.

    With tapers that size I probably wouldn't bother with reamers, there's plenty of room to single point bore them, and even just for a finishing cut a reamer that size is going to take some driving and the workpiece some holding - think distortion??

    If however you are modding a B&S taper reamer, back the cutting angle off or it will chatter like hell in bronze, where as the D bit won't.

    As for clearances - tapers and angles can do funny things.... I'd look at leaving the body machining until you have the cones as accurate as you can get. - IME when working with tapers, it's a lot easier to get a known clearance working from a square seating...... allowances for shim washers under the cone seats can be beneficial.

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    I have it set up in the lathe and have started to cut the taper, I agree that this is the best option, however, I am struggling to get a good finish at the speed I am turning it (quite slow) and also the finish at the water port (intermittent cutting) is just not good enough for an adequate seal. My plan was to machine the taper a few tho under size and then put the finish on with the reamer. I agree that trying to ream all of the material out could cause a problem.
    I am going to machine the cones and leave material on the faces so that I can skim them to the correct clearance during assembly, that way I can accurately measure (the originals were quite cut by the steam) each one and easily reproduce on future injectors. This is my first attempt at an injector so I am measuring everything ten times and cutting once!
    I can mail you some pictures, if your interested PM me your email address.
    Regards
    Steve

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    Added way too late but maybe useful to somebody

    Quote Originally Posted by Buchanman View Post
    Hi,

    Are you sure it is 1 7/8" BSP ? 1 1/2" bsp is 1.882" outside diameter and tube is usually 1.875" plus or minus 0.010"

    Buchanman.
    I'm also wondering exactly the same

    The OD on a pipe threads (BSP and NPS) are based on the pipe ID.

    The correct OD on a BSP 1½" (11 TI) is max 1.882 and min 1. 1.868.

    The OP will find that 1 7/8" (1.875) lies between those two diameters.

    Is BSP 1 7/8 really called out on a spec or is it something you've measured it to be?7

    Is it BSP (= NPS) or is it BSPT (= NPT)? When I write = don't take it too litterally as there are difference, not least in TPI.
    The main difference between use of a straight or tapered pipe thread is how they are sealed.

    Gordon

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    Hi Guys,
    Thanks for all your help and advise, thread and taper sorted.
    Best regards
    Steve

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    Quote Originally Posted by feet n inches View Post
    Hi Guys,
    Thanks for all your help and advise, thread and taper sorted.
    Best regards
    Steve
    Steve, great it got sorted out but what was it?

    Gordon

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    Hi Gordon,
    It was 1 7/8 BSP, when I was measuring the pattern injector I managed to find it in a table online but when I came to machine the casting I couldnt find it again, then some if the replies made me wonder if i had imagined it! lol. The taper refered to was for the valve seat and not the thread. I am trying to upload some pictures but im struggling at the mo.
    Steve

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    For future reference here's a BSP thread data table from a 1950's edition of Machinery's Screw Thread Book.



    Also from the same book, but not directly related to this thread, an interesting bit of information on metric conversion.




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