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Cutting long threads..

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  • old mart
    replied
    On a much smaller scale, I worked on a thread that was longer than the lathe centre distance. We had a Tom Senior mill which was worn and I wanted to make an antibacklash setup with a pair of new gunmetal nuts for the X axis. Fitting two nuts where one had gone before, and having to leave a gap between them for access to the Y axis leadscrew meant that I had to cut an extra 4" of 3/4 x 8 ACME thread on one end or loose travel on the X axis.. As the leadscrew was slightly worn in the middle, as is normal, I had to make the entire length of thread to match the most worn part. I used a fixed steady and a travelling steady as well as the tailstock to hold the leadscrew with bored soft jaws in the chuck. Fortunately the Smart & Brown model A spindle bore is 15/16" for the leadscrew which is about a foot longer than the lathe capacity. It is surprisingly easy to pick up such a coarse thread when it is juggled about in the lathe and even turned round during the refurbishing. The actual wear was only a small ammount, but would have meant loosing the benifits of the antibacklash if I had not bothered to do it.

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  • nc5a
    replied
    In the late 1970's or early 80's the remote power plant I worked in hired a world renowned GE Gas Turbine consultant during one of our major hauls. One of the jobs was to re-blade the compressor rotor. Once the rotor had new blades installed the tips needed to be ground for proper clearance. We didn't have a lathe or balance machine at the time to support and turn the rotor so the consultant had the millwrights build 2 pedestals with bearings to support the rotor at the bearing journals. Then a turning gear was fashioned to turn the rotor and a grinder pedestal to support the tip grinder.

    That wasn't nearly as interesting to me as the next fab job. As one would expect you have to be able to measure the diameter of the rotor tips to know when to stop grinding. The biggest micrometer we had was 24" and the rotor was roughly 6' in diameter. So the consultant had the millwrights and machinist make a couple micrometer frames in the sizes needed to do the job. The barrels and anvils from the larger mic were installed in the truss constructed frames. The cool thing about the truss frames is they were made from rebar and quite heavy. From what I understand they were very repeatable but took two guys to handle them.

    As stated in the beginning this is a remote plant so you can't just go to the store and buy what you need. We got pretty good at making do with what we had and keeping useful junk safe so it may someday be valuable..

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  • johansen
    replied
    That looks like a 4 start thread

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  • Toolguy
    replied
    Originally posted by wierdscience View Post
    Did they single point those leadscrews or mill them?

    https://www.youtube.com/watch?v=kbGbN_RNXAg
    That video shows thread whirling, a specialized form of milling. Thread whirling is used a lot for the medical industry, for implants and bone screws, etc.

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  • J Tiers
    replied
    If you look at that pic, behind the obvious lathe, there is another one, with a shaft sticking out of the headstock. If you look closer, that shaft seems to be sticking way out into the distance, either on stands, or otherwise held up.

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  • lynnl
    replied
    Upon revisiting this thread this morning, I now realize why I initially thought Rich's post (#2) led me to think it was describing long, continuous threads on a prop shaft: that picture in the OP sort of planted the idea in my brain.

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  • 754
    replied
    I am thinking they may have used the reversed lathe to drive the shaft. The taper and thread end against the main lathe . against a center in end of shaft. Then use that lathe to cut the threads.
    Then hook on/off controls together or the switches .

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  • Rich Carlstedt
    replied
    Yes, The shaft was 12 inches or so as I recall and not sure how much thread was needed, but it was on the end of the shaft.
    He said that during the war, they did many things you would never see in a normal machine shop

    Rich

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  • mickeyf
    replied
    Also confused here. All the propeller shafts I've seen only have threads aft of the taper on the end where the propeller itself goes. You should be able to thread that with a shortish lathe with a large enough through hole (maybe that was the issue?) and outboard support. I've seen prop shafts in the 6 in. diameter range, I suppose one for a large military ship could be several times that size?

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  • lynnl
    replied
    Originally posted by Rich Carlstedt View Post
    My father-in-law was a Tool and Die Maker ( and a fabulous machinist) and told me of the time
    during WW II when his shop was called by the US Navy and they needed a 40-50 foot propeller shaft with threads
    to have the threads redone , and could his shop do it ? Yes, they said and they did it although the longest lathe was 30 foot.

    ...(snip)...

    Rich
    I was having a hard time imagining why you'd need threads on a 40 to 50 foot propeller shaft. ...then as I started this reply, it dawned on me, we're probably not talking about threading the entire length.

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  • wierdscience
    replied
    Did they single point those leadscrews or mill them?

    https://www.youtube.com/watch?v=kbGbN_RNXAg

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  • Rich Carlstedt
    replied
    My father-in-law was a Tool and Die Maker ( and a fabulous machinist) and told me of the time
    during WW II when his shop was called by the US Navy and they needed a 40-50 foot propeller shaft with threads
    to have the threads redone , and could his shop do it ? Yes, they said and they did it although the longest lathe was 30 foot.

    The millwrights took two Lathes and relocated one so it was tailstock to tail stock and then coupled the feed shafts together..( U Joints and shaft)
    One Lathe drove the shaft and turned the leadscrews for the second lathe so the machinist could thread the shaft on that end.
    In time of need, ALL things are possible
    Rich

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  • 754
    started a topic Cutting long threads..

    Cutting long threads..

    I think this quaifies look at the 2nd lathe.. long stuff.
    I bet they use a tool kivkout at the chuck end on RH threads. Like Ainjest made. I think that is what Colchester used. Click image for larger version

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