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  1. #1
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    Default A one off use die for hard black poly pipe

    Gents,

    Something, I would like to bounce off the forum and see what comes up.

    I have a need for a 3/4" x 200mm (8") black poly riser, which I cannot buy-not made in that length.

    I have rung around the plumbers and it seems all the older guys had the right die at one time, but have have recently discarded them as soon as they heard I needed one.

    I really need the this riser in this length, I won't use steel as the cut and shut will rust from inside.I rather not use PVC as its not impervious to whipper snippers.

    So in a rush of excrement to the brain it came to me that a 3/4" metal socket with suitable slots cut in it might be substituted for a one - off die. I will cut down a 12" (300mm) poly riser and thread it.

    I can machine a slight taper -2 or 3 degrees- on the black poly.

    To the brains trust then Do you think it might work?

    Grahame

  2. #2
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    Default

    Can't see why not Grahame, the reverse method is used to make one off nuts.
    Kryn
    To grow old is mandatory, growing up is optional.

  3. #3
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    Default

    Grahame, whats wrong with single pointing a Parallel thread and take up the slack with thread tape?
    Rgds,
    Crocy.

  4. #4
    BobL is offline Member: Blue and white apron brigade
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    Default

    I've made a few of my own dies

    I use drilled holes to create the slots.

    This is a bit of tool steel and the scummy blackness is from the hardening process but for poly you could just use mild steel and not bother with hardening.

    Die.jpg

  5. #5
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    Default

    What sort of pressure will it be exposed to?

    As stated above, i would cut a parallel thread on a lathe with a single point tool. Teflon tape in the yellow or red (gas tape) should make a good seal.

    Simon

    Sent from my SM-G900I using Tapatalk
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  6. #6
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    Default

    brass threaded tube no good?

    there is also a Poly temporary meter spacer 20x 240l that is threaded both ends available from plumbing suppliers..probably bunnings etc as well

  7. #7
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    Default

    Pro pol pipe can be tricky stuff to thread, especially a tapered thread. I suspect a home made die will only end in tears. You need an inner insert to stop the pipe squashing when you start threading.

    Any decent rural plumbing supplier should be able to thread it if they know what they are doing. Generally power threading it also ends in tears.

    I thread it routinely in the larger sizes (2" and 1 1/2") and only ever do it by hand.
    Gold, the colour of choice for the discerning person.

  8. #8
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by .RC. View Post
    Pro pol pipe can be tricky stuff to thread, especially a tapered thread. I suspect a home made die will only end in tears. You need an inner insert to stop the pipe squashing when you start threading.
    Maybe so for larger sizes, but my experience is its better that it does squish because that's what it will experience when the female connector goes on. If an inner is used, too much material may be removed and this tends to create a sloppier thread. The hardest thing I found was holding the pipe while its been threaded- using those notched V shaped jaws worked but it sure mangled the outside of the pipe.

    I plumbed a small lab (4 taps and about a dozen junctions) with 20mm black poly using standard BSP dies and during the 17 year lifetime of the lab there were no leaks.

  9. #9
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    Hi Guys,
    Here is an update for you all. I am pleased to report I had no issues apart from the sometimes imminent collapse of the pipe in the chuck jaws - just about, but not quite and some marring as the jaws chewed up the plastic. It was expected as the material is as slippery as a butchers whatsit.

    If there is a next time around I shall definitely use an insert. The taper of 3 degrees was completed with a HSS parting tool. A sharp tool and go like a cut cat seems to yield a good finish.
    It gave a polished finish off the tool but does leave straggly bits at the corners. The fine swarf does not chip. The bulk of it can be rolled off the pipe when finished.


    The pipe has now been threaded and screwed into the right into the female elbows without a problem. I thought of RC when I used pink tape- hey! Just what was there at the time.

    Simon
    The pipe is a 10" riser fitted to my tap stand - so it is just domestic water pressure. I have not yet attempted a single point thread- something to now learn in my retirement.

    RC
    You had me worried there for a while and I elected to do some practice runs on scrap. If there's the next time I will use an insert to prevent crushing the pipe started to go triangular in the jaws at one point.

    Eskimo
    I was prepared to use brass and copper fittings if all else failed, but me being me, had to know if it was possible.

    If anyone is interested for future reference.

    The 3/4" Bunnings socket was cut with 4 parallel cuts with the diamond wheel- now sold in place of fiber wheels- It was just what was on the A/grinder at that time. A tapered plug (also from Bunnings was drilled for a 12 mm spigot to facilatate holding by the keyless tailstock chuck. Drilled and tacked to the 12mm, the plug was screwed into the socket.

    The socket being aligned to the pipe via the lathe cut its own thread reasonably cleanly.

    I used it with no power to the lathe- pulling it over by hand. The threads were a bit furry, not clean and sharp as per the standard manufacturer's thread. However, they were good enough to screw into the elbows with out any more efort than usual.

    Photos,yes I know you will ask? I have taken photos but I have a brand new phone and need to upload them to the computer.They will follow as soon as possible.

    Thank you all for your advice.

    Grahame

  10. #10
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    Default

    Quote Originally Posted by .RC. View Post
    Pro pol pipe can be tricky stuff to thread, especially a tapered thread. .
    Isn't the female socket parallel? No power threading was performed. The lathe was simply switched off at the wall and pulled over with the chuck key.

    The taper was cut on the pipe end only to better engage and center the cut edges socket

    When swarf ( fine plastic hair like fiber, not really swarf at all ) began to emerge from the cut slots in the socket, I began to feel much better about the attempt.
    The limit ing factor with the socket is its length.I could have gone a fraction more felt that was enough length to screw up into the elbow.

    Grahame

    The left side of the offcut pipe is the socket diecut one.The right hand side ( it was the original factory made thread) got a bit mangled from slippage in the vice jaws. I don't know what you could expect but this is good enough for me in that it scews up in the elbow and doesn't leak.

    Socket with slots cut.jpg3:4" plug and spindle.jpg3:4" polypipe die cut sample.jpg

  11. #11
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    BSP with both taps and dies comes in either straight BSPP or tapered BSPP, or for ISO nomenclature, G is the straight version and R is the tapered.

    Sockets are probably parallel simply as it makes the manufacturing easier.

    What generally happens when cutting tapered threads in pro pol is when you start getting a long length of thread engagement and cutting, the cutting tool digs in. it has taken me awhile to work out how to get good results.
    Gold, the colour of choice for the discerning person.

  12. #12
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    Hi Grahame,
    I have only cut one thread on that slippery black poly pipe, I found if you fold a piece of 120 grit sandpaper so that the grit is on the outside then wrap it around the pipe it grips it good enough without crushing the pipe.
    Bob

  13. #13
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    Default

    Hi Krisfarm
    Thanks for the tip. I probably won't need to use the die again for a long while, but by then I won't be able to remember what I was told here today. While not perfect visually, it does not matter as one end goes in the ground. It does not leak, so I am happy.

    It's all getting saved as notes so when the need arises, I shall have the necessary information ready to use.

    Thanks, everyone for your help.

    Grahame

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