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  • 3/4" arbor is too big

    I have an 3/4" arbor the needs to be max 5/8". My Jacobs 16n chuck has a max capacity of 5/8". The other end of the arbor is threaded I believe. I don't have a lathe (darn...) but was wondering if the arbor can be turned down to 5/8". Are arbors generally able to be reworked?

    Thanks for the help.

  • #2
    The arbor can be turned down. But your question begs the question of what this tool is, what machine it will be used in, and what you intend to use it for. Turning the arbor down may be a wasted effort if the tool, machine, or intended use aren't appropriate.

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    • #3
      It is part of a tapping head. I will call the manufacturer and see if there are appropriately sized arbors for my needs. Good to know that in the hands of a skilled machinist, the arbor would work.obviously the easiest route is a new 5/8" arbor.

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      • #4
        Oops. You answered the 'type' question already.
        Never mind

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        • #5
          Hi PT Doc
          obviously the easiest route is a new 5/8" arbor.
          Or a bigger chuck.
          Location: Long Island, N.Y.

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          • #6
            Originally posted by RichR View Post
            Hi PT Doc

            Or a bigger chuck.
            Jacobs doesn't make a larger capacity chuck for a 3jt. I noticed rohm does but I like the Jacobs and a new chuck will likely be costlier than a new arbor.

            Is there a way to mount a Jacobs 18n chuck (3/4" capacity) with 4jt on my drill press's 3jt. Btw, my drill press has a non removable 3jt. I guess a 4jt to 5/8" arbor on the 18n would allow it be mounted up in my 16n chuck but that intoduces all kinds of likely runout.

            Thanks again.

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            • #7
              Hi PT Doc
              Something like the SDA-075 listed here:
              http://www.zorotools.com/g/Clamp-On%...ters/00062076/
              might work. Maybe you can find something similar for less money on Ebay.
              Location: Long Island, N.Y.

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              • #8
                Procunier does not have smaller diameter straight shanks than 3/4". There are 3/8", 1/2" and 5/8" shanks on the procunier tapping heads on eBay. I guess they were all turned down by the users. What would be the best way to turn down a 3/4" arbor to 5/8"? Thanks again.

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                • #9
                  Originally posted by PT Doc View Post
                  What would be the best way to turn down a 3/4" arbor to 5/8"?
                  Without a lathe, it's a challenge. I've seen people use a drill press as a makeshift lathe (with a dead center in the table to support the work) using a file or rasp to remove metal freehand, but since you cannot chuck on 3/4", I think that's right out.

                  If you are willing to take a pass on the arbor with a file to confirm the file easily bites into soft metal (to make sure the arbor is not hardened), I would be happy to turn down the shank for you in my lathe for nothing.

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                  • #10
                    Just as a thought provoker, an adapter that was 3JT to match your drill press with a 3/4 inch female socket and set screw would hold the tapper without much worry about runout. It could be made perfectly concentric by doing a finish cut inside the 3/4 inch bore right in the DP. Such could be achieved with a boring bit held in a compound vise under the drill press quill. Sometimes you can make special purpose adapters like this from some commercially available taper blanks.

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                    • #11
                      The plan is to have it turned down in a lathe. I was wondering how you guys would approach this procedure in a lathe. Thanks

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                      • #12
                        Originally posted by PT Doc View Post
                        Procunier does not have smaller diameter straight shanks than 3/4". There are 3/8", 1/2" and 5/8" shanks on the procunier tapping heads on eBay. I guess they were all turned down by the users. What would be the best way to turn down a 3/4" arbor to 5/8"? Thanks again.
                        The 1E and 2E are available with 1/2" straight shanks but they might not be big enough for your needs.

                        bob

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                        • #13
                          Originally posted by PT Doc View Post
                          The plan is to have it turned down in a lathe. I was wondering how you guys would approach this procedure in a lathe. Thanks
                          Depends on what tooling is available.

                          If all I had was a 3-jaw, and the arbor is already centerdrilled both ends, I'd turn between centers. Assuming this is a threaded arbor, I'd use some aluminum in the dog to protect the threads.

                          If I didn't have a 4-jaw nor a dog or if the threaded end was not already centerdrilled, I would chuck a piece of scrap, then drill, bore, and thread it to accept the arbor. Hopefully, the far end has a centerdrill for center support, though if not, a steady rest could be employed in order to make a centerdrill. Alternatively, a follow rest could be used instead of centerdrilling.

                          The easiest way though would be the chuck the whole thing (tapping head still attached to the arbor) in a 4-jaw (with some aluminum shims to prevent the jaws marring the work). Again, hopefully the far end has already been centerdrilled, or other methods of adding support will need to be used as noted earlier.

                          If the far end is not centerdrilled and no steady is available, the shank could be indicated in on a mill and centerdrilled there. You could even use a reasonably accurate drill press, though in that case, I would probably scribe the end of the arbor and give it a healthy centerpunch first.

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