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Threading Chuck Adapter

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  • Threading Chuck Adapter

    I have a Woodhouse and Mitchel lathe that has a 2.5-4 spindle thread. I have a new 4 jaw chuck for it and a rough cast adapter plate. After giving some thought on how to thread this I came up with the following procedure. I haven't done the job yet so let me know if this is a good idea. I thought I should make a stub shaft with the same thread dimension as my spindle. I can test fit this stub shaft on my existing 3 jaw adapter plate. I can then thread my rough cast adapter plate using the stub shaft as a sort of "go-no-go gauge". I have another lathe to do all this in so disturbing this set up won't be an issue.Am I one the right track or is there a better way?

  • #2
    With a total of 2 backplates on my resume I'm no expert, but that's exactly what I did. I did 3 wire my spindle first for a dimension to match on the test stub. Did it in Alu too. I dunno why .....

    Well it was easier to cut!

    SP

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    • #3
      There is nothing wrong with making the test shaft in aluminum for a one off job like that. I do that all the time for oddball jobs.
      Mark Hockett

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      • #4
        I've done a couple of back plates and some other tooling that mounts directly on the spindle threads. The most important thing, in my humble opinion, is doing all the work on the threads and back surface in a single set up. You don't have to have a precision set up, I've done it with an old, worn out three jaw that has over 0.020" runout. Just do not take it out of the chuck until the work on the mounting area is completely done.

        A stub gauge is good, but I saved the time and insured a better fit by just unscrewing the chuck and reversing it to try the new mount. The new mount was still firmly held in the chuck which just hangs out there. One caution when testing the fit, screw it on slowly and STOP as soon as you feel any resistance. Take it back off and cut the threads or so called "registry" deeper. Don't go for a real tight fit. That is not necessary as the Vee threads are self centering and will remount within tenths. I leave at least 0.002" all around: it could be more. The so called "register" is not a functional part of the fit. It is just a clearance hole for the unthreaded part of the spindle next to the shoulder. LEAVE CLEARANCE there. I suspect many try to make the fit too tight and wind up with a back plate frozen on the spindle. Check the forum archives, there are many stories.

        After the mounting area is cut, you should do the rest of the machining with the back plate mounted on the spindle it will be used on. This ensures the best possible concentricity. Do clean both the spindle threads and the backplate threads and back mounting surface religiously for this operation as any chips on the threads will ruin the fit and the subsequent machining would be off center.
        Paul A.

        Make it fit.
        You can't win and there is a penalty for trying!

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        • #5
          Originally posted by Paul Alciatore
          A stub gauge is good, but I saved the time and insured a better fit by just unscrewing the chuck and reversing it to try the new mount. The new mount was still firmly held in the chuck which just hangs out there. One caution when testing the fit, screw it on slowly and STOP as soon as you feel any resistance. Take it back off and cut the threads or so called "registry" deeper. Don't go for a real tight fit. That is not necessary as the Vee threads are self centering and will remount within tenths.

          Do clean both the spindle threads and the backplate threads and back mounting surface religiously for this operation as any chips on the threads will ruin the fit and the subsequent machining would be off center.
          Did the exact same, has now worked fine several times.
          1601

          Keep eye on ball.
          Hashim Khan

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          • #6
            I believe that is a well recognized way of doing the job correctly.When I made a new spindle fitting to accept my chuck from my other lathe,(the spindle needed a larger adaptor)for my new wood lathe that's exactly what I did and I have kept the working spindle for future jobs should it be needed.Alistair
            Please excuse my typing as I have a form of parkinsons disease

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            • #7
              How much do the chuck and backplate in question weigh? When I did the new backplates for my 17" leblonde I made a stub shaft. I thought about reversing the chuck just like j tiers and Paul did but after I started to set it up I realized that it wouldn't be any fun to try and check 70 pounds of chuck and backplate by taking it on and off. I did the work in a 10" 3 jaw. So in my case I decided to go ahead and make the stub.

              -brian
              -brian

              Hello, my name is brian and I'm a toolaholic.

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              • #8
                Thanks for the info everyone. This adapter and my current three jaw would be over 90 pounds so I would prefer not to unscrew it and turn it around to check fit.I think it will be easier to set up in my other lathe and use a test stub. I won't be able to get at this project for about a week. I'll be sure to take photos and post them.

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