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Thread: Boring Center Hole in Chuck

  1. #1
    Join Date
    Jan 2017
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    Default Boring Center Hole in Chuck

    Hi, I'm new to the site.
    Thinking of buying a 7x16 lathe or maybe 8x16. What I need is a 4 jaw chuck with a thru hole of 1.2" maybe just a little larger.
    All the 5" 4 jaw chucks I have found have a bore hole of 1.18". 6" 4 jaw chucks have a bore of about 1 1/2".
    Is a 6" chuck to large for a 7x16 lathe?
    Could I bore out the 5" chuck 0.05" without problems?
    Thanks

  2. #2
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    A 6" chuck is likely to be inconveniently large, but might be used.

    I would not bore a chuck as a first choice. Certainly not without taking it apart to see how much material there was to cut into. They may be hardened somewhat also to reduce wear on the jaw slots, which may affect the process.

    That said, a tool is just a tool, and if the small added diameter and depth is worth the trouble and risk, then you may as well.
    1601

    Keep eye on ball.
    Hashim Khan

  3. #3
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    Default

    Thank
    Hadn't thought of the hardness issue.

  4. #4
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    The bore of the spindle on an 8x16 is only 3/4". Stu

  5. #5
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    Jan 2017
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    Thanks. I do realize this. The work I need to do will all fit within the chuck.

  6. #6
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    Quote Originally Posted by Jdaniel343 View Post
    .......Is a 6" chuck to large for a 7x16 lathe?.......
    Maybe. It depends on if the larger chuck has longer jaws. I don't know if they ALL do but I suspect it's likely. The same piece in a 6" chuck might result in the end of the jaws contacting the ways but in a 5" chuck they might clear the ways. Just something to check out.

  7. #7
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    I would not be concerned about boring out 20 thou inside a 5 inch chuck - only 10 thou removed.

  8. #8
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    Default

    There's a number of reasons for going with the smaller chuck. A lot of times you will mount up and run a part where the jaws stick out past the OD of the chuck.

    So a 6" chuck on a 7" swing lathe is way too large. You will frequently find that the jaws stick out past the OD far enough will foul the bed. Keep in mind that on the 6" the jaw only needs to stick out past the OD by 1/2" before this occurs. With a 5" chuck this is less likely to occur but would still an issue with some range of sizes that would other wise be able to mount in the jaws. Maybe not the 1.2'ish size bar stock but certainly with some other larger parts that you'll turn from time to time. A 4" four jaw would likely be a pretty much ideal size as by the time the jaws can strike the bed the jaws would be sticking out so far as to be both useless and dangerous due to having so little of the jaw engaged with the body.

    It also explains why the normal stock size of four jaw that you can buy to use on these 7x lathes appears to be a 3 inch size. Keep in mind too that the 7" mini lathes use the integral back plate on the spindle to mount the chucks. So you have to buy a chuck that is set up to be mounted in that manner. This limits you to chucks that are set up with threaded holes for the studs that are used with this style of lathe.

    There is another issue that you may not have thought about. The 7" and 8" mini lathes both seem to share a MT3 spindle taper. The mouth size for an MT3 is only 0.94". So even if you bore out the chuck body to 1.2" like you wish for you will still only be able to insert a 1" to 1.15" hunk of stock into the chuck until it encounters the spindle. If that's enough for your needs then great. But if you figured on shoving longer stock through the spindle then it's not going to work.

    As for actually doing the machining I think you'd be fine. Chucks that are this inexpensive are unlikely to be hardened. In fact I suspect the bodies for this sort of price point would be easily machined cast iron. But since it looks like a 4" size chuck is just about maximum to use on such a machine due to the jaw protrusion issue you would need to carefully inspect the body casting from the rear to be sure you do not machine through into any hollow areas. And that becomes far more likely when you're talking about a roughly 7/8" through hole being machined out to 1.2". Even if it does not cut through into any hollows you would want to leave the thickness of the center "tube" within the casting at least 3/16" thick. And opening the radius by roughly 3/16" is going to be a pretty serious risk of removing most of that metal.

  9. #9
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    Quote Originally Posted by Arcane View Post
    Maybe. It depends on if the larger chuck has longer jaws. I don't know if they ALL do but I suspect it's likely. The same piece in a 6" chuck might result in the end of the jaws contacting the ways but in a 5" chuck they might clear the ways. Just something to check out.
    Might as well whack off half inch from the end of the jaws. Not ideal, but workable solution if nothing else works out.

  10. #10
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    As it is a four jaw chuck, there is little going on around the bore that opening it up a few thousandths would effect. The bodies are usually cast iron or semisteel and machine easily. If hardness is a concern, it is a simple matter to check it with a file.
    Jim H.

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