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  1. #1
    Boringgeoff is offline Try not to be late, but never be early.
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    Default Cutting a coarse left hand thread.

    Hi,
    I'm in the throes of making a replica of a multi head fence post boring machine. This machine was made by/for a farmer in the south west of WA after WW1. Part of it consists of two shafts about 18 1/2 inches long, they have a conventional thread on twelve inches of their length which is 3/4 UNC (or Whitworth perhaps?) Cut into this is a counter clockwise thread of extremely coarse pitch of 14 threads per foot.

    Multi head drill 001.jpgMulti head drill 002.jpg

    My question is: is there anyone here who would be interested at making these for me, preferably from WA?

    Cheers,
    Geoff.

  2. #2
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    Default

    Hi Geoff,

    Cutting threads that coarse on most lathes can be a problem, the best solution is to find someone with a cnc vertical mill and a 4th axis..

    Ray

  3. #3
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    Default how critical is the pitch ?

    14 tpf(oot) is 1 1/6 tpi, that's an odd size

    a 20mm metric thread is about 15 1/4 tpf(oot), is that close enough ?

    what are you doing for the corresponding nuts ?

    If you need to remake these, then a 20 mm thread should be ok ?

  4. #4
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    Default

    Quote Originally Posted by RayG View Post
    Hi Geoff,

    Cutting threads that coarse on most lathes can be a problem, the best solution is to find someone with a cnc vertical mill and a 4th axis..

    Ray
    Ray!!
    or someone who can do helical milling

  5. #5
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    Default

    Many people *could* cut those. I certainly have the equipment to do it.

    Question is, is this a paying job or a 'slab of beer' deal?

    Second question, is there a drawing to work off?

    Third question - what about the female threaded part (ie a nut or threaded item the rod screws into)?

    You get the idea - more and well detailed information required.

    PDW

  6. #6
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    Quote Originally Posted by Steamwhisperer View Post
    or someone who can do helical milling
    I've just started doing some of that myself. For a simple process it is very satisfying. Willing to help if necessary.

    Michael

  7. #7
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    Default

    This is simply a modified bit similar to a "brace and bit", as used to drill holes in fence posts. I use them a bit but I only have the ordinary type. The device is apparently used to drill multiple holes with multiple bits like this. It would have been used to drill multiple holes in fence posts to pass the wire thru. I don't think anybody puts wires thru the posts like that any more. It is much easier to attach the wire reel to the ute and drive down to the other end of the fence. Staples to attach the wire.

    Dean

  8. #8
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    Default

    On the other hand I may be wrong about this.

    Dean

  9. #9
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    Default

    Staples are a lazy man's fence. Only good use is on cyclone wire fence.

  10. #10
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    Quote Originally Posted by Oldneweng View Post
    I don't think anybody puts wires thru the posts like that any more. It is much easier to attach the wire reel to the ute and drive down to the other end of the fence. Staples to attach the wire.
    Quote Originally Posted by Nifty Nev View Post
    Staples are a lazy man's fence. Only good use is on cyclone wire fence.
    I suspect that Geoff is making a copy for historical interest rather than stock control though...

    (Geoff, given the age of the device it is more likely that it is a Whitworth thread. UNC was a circa WW2 invention I believe.)

    Michael

  11. #11
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    Quote Originally Posted by Boringgeoff View Post
    ... Cut into this is a counter clockwise thread of extremely coarse pitch of 14 threads per foot.
    Looking at the pictures again, I think it misleading to call the coarse pitch groove a thread. It reminds me of a fly press I once saw with a similar arrangement. The fine thread would have a normal nut (or nuts) on it and were probably used as stops. The helical groove would be used for some sort of drive or maybe rapid travel. Because of the groove pitch it could not use a conventional nut. The more likely situation would be a close fitting sleeve with a pin or dog point screw locating in the groove.

    Michael

  12. #12
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    Default so the coarse thread pitch is not critical, it's just to evacuate the chips

    This looks like an easy lathe job, just needs a form tool to cut the coarse thread.

    Fine thread can be Whitworth or UNC, it's just to drive the bit forward

    But.... what about the cutting edge, bit of tool steel or carbide brazed in perhaps ???

  13. #13
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    Quote Originally Posted by johntopp View Post
    This looks like an easy lathe job, just needs a form tool to cut the coarse thread.
    For your average lathe, trying to cut a 1 1/6 tpi will put too much strain on the leadscrew and drive train. An 8tpi leadscrew (common size) probably shouldn't attempt anything under around 4tpi. Not to say it can't but damage could ensue...
    Helical milling is probably the less stressful way to go.
    Michael

  14. #14
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    Default

    It could be for cutting/forming a thread in to hardwood posts for gate hinges, basically a Tap.

  15. #15
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    Quote Originally Posted by johntopp View Post
    This looks like an easy lathe job, just needs a form tool to cut the coarse thread.
    There speaks a person who has never cut a coarse thread.

    I have a 2.6 tonne Monarch CY lathe with a 7.5HP motor. The coarsest pitch it has in it's gearbox is 2 TPI. Slowest speed is 13 rpm. I've cut 2 TPI LH threads on it. This thread is almost double that *and* on a long, skinny, highly flexible piece of threaded rod so it's going to move and chatter badly. A travelling steady is going to be essential and given the threaded profile, possibly one with a guiding bush.

    The sensible way to make this is to use a ball nosed end mill on a milling machine or a lathe with live tooling. This job is a PITA waiting to happen and unless it had to be dead nuts original for a very important piece of industrial restoration for a museum or similar, or it involves a nice collection of folding money, it's best not touched. Especially absent any photos, drawings or other details of what it fits into.

    PDW

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