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Thread: Interesting Lathe Speed Numbers

  1. #1
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    Interesting Lathe Speed Numbers

    How fast would you spin a 14" diameter bowl?

    In a discussion on the World of Woodturners site, Richard Raffan posted a picture of a 14" red gum bowl that detonated while he was turning it. It happened while he had stepped away from the lathe, so he was well out of the line of fire when it blew. This was wood that was riddled with voids (gum pockets) and is known for being tricky to keep in one piece.

    Later in the thread Richard mentioned he "wasn't spinning the wood that fast", somewhere around 1000 rpm for the 14" piece. Another poster mentioned that there are about 200 Gs trying to rip the rim off a 14" bowl spinning at 1000 rpm. Yet another poster said that reducing the speed to 700 rpm would cut the G forces in half. Reducing to 500 rpm would be one fourth of the G forces as 1000 rpm. (Smaller diameter pieces would have lower numbers and larger pieces would be higher.)

    I just thought those were interesting (and eye-opening) numbers. Something to think about the next time you're cranking up the speed on the lathe to get a better cut. Richard has been a professional woodturner longer than I've been driving cars, so I'm sure he felt comfortable turning a piece that size at that speed. I don't think I would be.

    When I started turning, I kept the speeds pretty low, because catches were all too common, and low-speed catches were less dangerous and destructive. As I've gained turning experience, I'm bumping the speeds higher and higher, since I get a better cut when the lathe is spinning faster. I've gotten very comfortable with a bowl gouge, and catches are very rare (and typically very minor) these days, so the risk of catastrophe feels lower to me than it used to. Still, 1000 rpm on a 14" piece would feel awful fast to me. (My current limit for finishing cuts on a piece that size would probably be around the low to mid 800s.) I'd probably love the cut I could get at 1000 rpm, but in the back of my mind would be this little movie running, showing how quickly an edge could break off and stick into anything in its path.


    So...how fast would you spin a 14" bowl?
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

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  2. #2
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    What is a "lathe".......... I forget......
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

  3. #3
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    Quote Originally Posted by Stuart Ablett View Post
    What is a "lathe".......... I forget......
    It's that thing you're buying the SawStop bowl drying table for.
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

    workingwoods.com

  4. #4
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    Very early in my bowl turning career, which was a short career at that, I received two redgum bowl blanks 8" square and 2" thick. I do not recall the speed I was turning when the first one blew apart but I was wearing my faceshield at the time. I immediately thought that the problem was speed as I did not know that this wood was prone to flying apart.

    To answer your question I may have turned a 14" bowl as fast as 1000 rpm but I doubt it. I am a bit of a chicken when it comes to turning larger pieces.
    I turn boxes at 2200 or more RPM but they seldom exceed 3 or 4 inches in diameter.
    I may be getting a little older physically but mentally I'm still tarp as a shack.

  5. #5
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    chevrolet 11 1/2" clutch.....350 small block.......6500rpm......


    oh-yeah......lathe
    [SIZE="1"] associated with several importers and manufacturers.[/SIZE]

  6. #6
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    Quote Originally Posted by Vaughn McMillan View Post
    It's that thing you're buying the SawStop bowl drying table for.
    Funny guy

    The forces involved are eye opening, to be sure. I always knew that rim speed of a 14" bowl was a LOT faster than say a 6" bowl, but the Gs produced is really something

    Myself, I turn as fast as I "feel" safe, and that has a lot of variables, like the wood the thickness of the wood and such, I will admit to being somewhat fearless, but, I hope, not too stupid, for example, I always wear my Triton powered respirator when roughing, for a number of reasons, all dealing with safety; one, the face shield/helmet combo is quite robust, and would help a lot if one really exploded, two, the respirator part of it keeps the dust on the floor, instead of my lungs, and the third reason is I get a lot fewer chips down my shirt with the Triton on

    I've also learned how to stay out of the line of fire, but that is a bit of a false sense of security, sure, if one goes "BANG" and you are not directly in the line of fire, that is good, but I'm sure most of us have our lathes against a wall, so ricochets are always a problem

    Good info just the same!
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

  7. #7
    Just get rid of that vs lathe and go to a 3 pulley, a lot less decissions to make that way

  8. #8
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    Vaughn, Like you say Richard Raffan has been turning since before I could drive. But I have not found all that much need even on a 8" or 9" bowl to go over 750 to 800RPM to get a good finish cut or shear scrape with a bowl gouge. Like you say, as I have gotten more comfortable with my tool control the speed has come up but I understand about the rotational forces at work and quite frankly it is pretty scary if a bowl or other large chunk of wood comes apart.

    While I always wear a Uvex Bionic faceshield when I am roughing a bowl. I still just like to wear my safety glasses when I am really getting into the final shaping of a bowl. Hearing stuff like this always makes me think twice about that.

    Vaughn by the way how can I get invited to participate on the World of Woodturners site? I would love to get an invite.

    Thanks,

    Alan

  9. #9
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    1000RPM seems quite fast to me too...Having a bowl come apart while nothing is touching it would make me turn the speed down quite fast, er I mean slower.

    Most of my finish turning is down at about 700rpm. Then again if a blank is pretty balanced so is the roughing. Belt changing although not hard ranks right up there with cleaning up the curlies for me...that doesn't happen very often either.
    A man is rich in proportion to the number of things he can afford to let alone. -Henry David Thoreau
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  10. #10
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    Interesting facts!

    Very interesting information!

    As far as what I turn big bowls at, it depends. If it's a solid chunk, then I turn the speed up. With one that has punky areas, or a large number of voids, I think I would keep it around 800 rpms or less. But I suppose the mass of lathe matters as well. I maybe have too much confidence with the speed, just cuz the ole' Rollstone, is around 1500 lbs. Also, when I do choose to bump it up, I make sure my body isn't in the "throw" path. That way if something does happen, I will be well to the inboard side of the piece as the projectiles fly out. I know this isn't foolproof, but it's kept me bruiseless so far.

    Hutch

    P.S. BTW I have turned a 20" bowl at around 600 RPMS. It was very well secured, and the speed was very critical to producing the finishing cuts at the 1/2" rim. There was so much flex that the chatter was causing serious issues. In situations where the rules of the road are streched (or broken) I am always aware of the dangers. I make sure that I "test the waters", away from the lathe at the circuit breaker, before I approach such a workpiece. I don't want you to think that I am careless or reckless.

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