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Off-center turning

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  • tlfamm
    replied
    "many of the members here are very new to machining"


    exactly the motivation for the OP.



    I reread the entire thread, and while there are definite opinions expressed, I don't see anything I would characterize as flack - to include a complete absence of personal malice, and insults against the sainted name of Bridgeport ...

    Leave a comment:


  • Carld
    replied
    Why is it getting more flack, I don't know. The reason John's article didn't get much flack is he used a four jaw chuck. Any time you put something larger than a piece of shim to protect the work surface you have a chance of slinging it out and getting hurt. With the piece off center as much as it was in the 3 jaw it would have to be run slow so the chance of it flying very far is slim.

    Yes, I meant to say safer.

    The reason I have said anything at all is because many of the members here are very new to machining and if they see something like that setup they may think it's ok and try it. Since they don't have a clue about the danger of it getting slung out of the chuck they may start the lathe at 300 rpm or more and the lever effect of the off center weight would/could sling the chunk out with a vengeance in the direction of the operator.

    I have seen alleged machinists at places I worked do things just as dangerous more than once. You would think after the first failure they wouldn't do it again.

    Not intending to offend anyone, just pointing out any dangers.
    Last edited by Carld; 03-10-2011, 11:10 AM.

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  • fciron
    replied
    Originally posted by Carld
    No I didn't see that. I would feel better if the spacer was welded to the piece in the 3 jaw and even that is chancy. He could weld a stub on the end of the chunk that is offset the distance he needs. There's a few ways to make it work.
    Italics mine. I think what you meant was "There's a few safer ways to do it."

    It's not a set-up I'm going to replicate, nor would I recommend it to anyone else, But I, too, wonder why this is getting so much flack. Any large offset mass is going to require the lathe to be slowed down and the cuts to be lighter. Packing pieces are used in all kinds of applications, both packing pieces and shims are going to reduce the grip between parts to some degree.

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  • Westline
    replied
    John
    I just checked your thread ... really nice job.
    That one will go into my bag of tricks next time I need to machine a strange part.
    I know the whole issue with my setup was safety and honestly I knew I was going to catch some flack and I'm fine with that.
    Getting back to safety here is a interesting video that will let the people that hide behind "safety first" think a bit.
    http://www.youtube.com/watch?v=IRVdiHu1VCc

    Leave a comment:


  • John Stevenson
    replied
    Anyone remember this thread ?

    http://bbs.homeshopmachinist.net/sho...ight=eccentric

    I didn't get as much flack over this and it wasn't that different.

    Leave a comment:


  • Westline
    replied
    Originally posted by winchman
    You can also use a combination of inside jaws and outside jaws for holding irregular shapes and doing off-center turning.
    Thanks did not think of that, pretty clever.

    Leave a comment:


  • winchman
    replied
    You can do off-center turning in a 3-jaw by starting one or two of the jaws early as you put them in the chuck. Just turn the chuck key enough to advance the scroll the desired number of full turns before inserting the other jaw(s). That avoids having to use spacers.

    You can also use a combination of inside jaws and outside jaws for holding irregular shapes and doing off-center turning.

    It works, but a 4-jaw is better if it's available.

    Leave a comment:


  • Carld
    replied
    That may be true but why temp fate. To continue doing something that is dangerous will get Murphy's attention.

    I learned long ago it's best to not do something that looks dangerous.

    I don't use the, "Watch this" red neck approach anymore.

    Leave a comment:


  • fciron
    replied
    He did make it work and lived to tell the tale.

    Leave a comment:


  • Carld
    replied
    No I didn't see that. I would feel better if the spacer was welded to the piece in the 3 jaw and even that is chancy. He could weld a stub on the end of the chunk that is offset the distance he needs. There's a few ways to make it work.

    Leave a comment:


  • John Stevenson
    replied
    Dis anyone read the part where he said he didn't have a 4 jaw chuck ?

    Anyway South Africa is a long way away, should have stopped bouncing way before it reaches here, let alone the US.

    Leave a comment:


  • Lew Hartswick
    replied
    I certainly wouldn't offset anything THAT FAR in a three jaw. I have
    done an offset of about 0.030 or a bit more making a cam for the
    tool holder I built. That was a 0.500 round and I wanted a
    pull distance of about 0.030 to 0.035 so it was not a big deal.
    I even used a tailstock centre to steady the part.
    BUT when the offest gets as big as that shown, NO WAY am I going
    to do it in a 3 jaw. :-)
    ...lew...

    Leave a comment:


  • Carld
    replied
    well, I'm glad that was a demonstration of what not to do. To be honest I set up like that once and when I looked at it and thought about what may happen I switched to a four jaw. It probably saved me from getting hurt.

    Leave a comment:


  • Westline
    replied
    Originally posted by Carld
    I certainly would NOT do that in a 3 jaw chuck. If you do an offset such as that use a 4 jaw chuck, it's much safer. Having that piece of brass in there with the chance of things shifting and the brass flying out is not a good idea.

    It's hard to balance a setup like that, just run it at the speed that feels safe and start slow and work your way up.
    I posted this in a extreme case of " kid's don't try this at home"
    It's was more a case of what can be done but shouldn't.
    If I stop posting It just means Darwin was right and my tools took me out.

    Leave a comment:


  • Carld
    replied
    I certainly would NOT do that in a 3 jaw chuck. If you do an offset such as that use a 4 jaw chuck, it's much safer. Having that piece of brass in there with the chance of things shifting and the brass flying out is not a good idea.

    It's hard to balance a setup like that, just run it at the speed that feels safe and start slow and work your way up.

    Leave a comment:

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