The need for speed

Discussion in 'Newbie' started by Rick Prosser, Apr 17, 2009.

  1. Rick Prosser

    Rick Prosser

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    Does running the lathe at a higher speed make better finish cuts than slower speeds?

    I know we need to run slow speeds for roughing bowls and out of balance pieces so chasing the lathe across the room is kept at a minimum.:D

    Spindle turning seems to run a higher speed (in general) than bowl turning, but I have seen pro turners running high speed for bowls and boxes.

    What is it about running at high speed that gives a better result?
     
  2. KurtB

    KurtB Moderator Staff Member

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    Speed

    Rick,
    One of the things that higher speed does is allow you to cut with less force, as long as the tool is properly presented to the wood. In the case of spindles or finials, this means less lateral (sideways) pressure on the piece with less vibration.

    The speed you turn should be based on the diameter of the piece; so, spindles and finials would turn at higher speeds than bowls. A lot has to do with the 'pucker factor' of the turner!:)
     
  3. MichaelMouse

    MichaelMouse

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    No. Try his simple experiment if you aren't a regular viewer of Roy Underhill. Have someone rotate the lathe for you at a couple,three RPM and swoop your cutting tool in as you would normally do, only in slower motion. If the tool is sharp, you'll make a wonderful shaving and leave a nice smooth surface. Sort of like carving, where the piece isn't moving at all.

    If the piece is rotating at 600, every point comes by the tool ten times in a second. That's whether its an eighth inch finial or an eight inch cylinder. If you're skewed to remove a shaving 1/10" wide, means you have to move at a little less then one inch per second to get a clean cut. If you're in a hurry, speed up. I'm a pleasure turner, so an extra five minutes on a piece doesn't bother me. I seldom, if ever, cut as fast at an inch per second, and generally a bit broader than a tenth of an inch, so I get a pretty regular surface.

    The extra speed may actually hurt you in a couple of ways. First, it will allow you to rip with a dull(er) gouge, making an inferior surface, because the piece has more energy at higher rotational speeds. Second, if you break the piece or the hold, it'll hit you harder. Since Newton's third says action = reaction, the harder the wood hits the tool, the more it rebounds. The flex seems to overcome any benefit gained in rotational inertia as far as I can see.
     
  4. Joe Greiner

    Joe Greiner

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    It all boils down to surface speed, to some extent. With all due respect, Mouse's arithmetic is prone to misinterpretation. I have some optimizing charts of diameter vs. speed in rpm around someplace, but can never find them, of course. What you've observed is mostly the experience of the turner, and the turner's comfort level.

    Your pucker factor will change as you gain experience with different shapes and materials. Good judgment is the result of experience. Experience is the result of bad judgment. "Learn from the mistakes of others. You don't have time to make them all yourself." - Eleanor Roosevelt. You need all of these.

    Cutting "the wood as it wishes to be cut" is hard to beat as advice. Sharp tools, and slicing vs. chopping, will generally produce smoother surfaces.
     
  5. Bob Edwards

    Bob Edwards

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    Speed

    This is another one of those questions that you will get a different answer from each turner you ask. It never fails during a demo that someone doesn't ask "what speed are you turning at" My answer is always "I haven't a clue". I heard one well known turner answer the question,"I turn the speed up 'til I get scared than I back if off a little" I'm not that daring and I dare say I turn at a slower speed than most but the obvious answer is that speed has it's place. For example when turning a square edge piece or one with large voids I generally turn the speed up quite a bit. With a square piece consider that the tool only touches the work 4 times per revolution. The faster you go, within reason, the more often the four points come around and the smoother the cutting process will become. This is where the scary part comes in!!
     
    Last edited: Apr 18, 2009
  6. Vaughn

    Vaughn

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    That has been my experience, too. I get fewer catches and smoother cuts than I used to, and I'm also running at quite a bit higher speeds than I used to. I attribute the better cuts to experience I've gained in presenting the tools more than the increased speed, though.

    I do find, though, that higher speeds (within reason) tend to produce smoother cuts and fewer catches when I'm blind hollowing with a captive rig.
     
    Last edited by a moderator: Apr 25, 2009
  7. Dave Ogren

    Dave Ogren

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    I think that is a really great question. I am a new person to the turning world. Two weeks and about 9 bowls to my credit. In the metal industry there are speed and feed charts depending on what the tool is. I have not found that with wood, wish I could. I am turning faster and faster Currently roughing out a 14" cherry bowl at 1400 RPM's. Even on the out of balance blanks I am running them faster my lathe is bolted to the floor (no walking) so I watch to see if the screws holding the blank to the face plate are becoming loose. Usually I have to take the faceplate off once or twice to tighten up the screws, until I get the blank round and away from the intermittant cuts. I hope someone knows the answer.

    Dave in Asheville
     
  8. GeorgeH

    GeorgeH

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    In addition to wood turning, I also do wood carving. I can tell you with a high degree of confidence that the "speed" and degree of force with which the cutting edge contacts and passes through the wood is less important than how sharp the cutting edge is in the first place. No degree of speed will make up for an edge that is not sharpened to its optimal edge. So, I guess you cold say I'm back in MM's club again.
    IMO, if you want to turn at production speeds then crank it up and go for it. Personally, I like to take my time and enjoy the total experience.
     
  9. Mark Warden

    Mark Warden

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    Hi Dave I'm pretty new to turning also but one thing I can tell you for sure is if your screws are coming loose your pushing it too far. And another thing I learned is at higher speeds you build up more heat and you can crack a green piece of wood from heat buildup and once it cracks it can literally explode. Just a step in the learning curve I thought you might what to bypass. Happy turning:cool2:
     
  10. Kefferpl

    Kefferpl

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    Speed

    Seems like i remember something of a formula used in spindle work Diameter * speed = 9000 ? Anyone else seen that
     
  11. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Dave, 1400 RPM is too fast for roughing. I would even consider it faster than necessary for finishing cuts. The screws in the faceplate are trying to tell you something. If they get loose then they are very close to letting go altogether.
     
  12. KurtB

    KurtB Moderator Staff Member

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    Speed

    A rough rule of thumb is diameter of the piece x rpm should equal a number between 6000 and 9000. Please note that these are not rpm numbers. They are a guideline number. So if your piece starts at 14 inch diameter, then your starting rpm should be about 425, and as the piece gets rounder and smoother, you could get up to 642 rpms. I would definitely say that 1400 rpm on a 14" diameter piece would be hustling.
     
  13. MichaelMouse

    MichaelMouse

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    Leave cutting by the numbers to the CNC people. They have meaning there. Wood is not as homogenous as metal, and you can't make a constant advance into the turning as the X-Y drive does. As I mention a lot, you can't even present the tool at the same sharpness angle after you sharpen, either, which means that precision-grind jigs are unnecessary. You vary your sharpness/skew/clearance angle so that it produces the best shaving and as little pressure on your guiding hand as possible. That will change CONSTANTLY as your angle to the grain changes, as in bowl making.

    This is hand work. "work of risk," if you will, though some apply scrapers and lasers through limiting jigs in an approximation of machine - no risk - work. If the product rather than the process is your aim, enjoy. Just don't expect to use someone else's thumbs to do your work.
     
  14. Frank F

    Frank F

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    I'm in the speed can't compensate for dull tools or flawed technique camp. The only time I've found a little extra speed helpful is with interrupted turning or turning the ghost. The speed makes the voids pass quicker and the ghost more visible. The tool has less time to enter the space. Obviously when turning the ghost, LIGHT cuts are a must at any speed, otherwise the tool will find a void.

    When I say a little extra speed, I don't mean to crank it up so the wood looks a solid blur. Be reasonable.

    I realize that I may be compensating for bad technique, but so far this works for me.

    On the flip side, slower speeds are a great diagnostic tool. Sometimes when I can't get the tool to do what I want, I slow down to 100 to 150 rpm to see exactly what's going on: what I'm doing wrong. NOTE: If you can't get a good shaving at 100 RPM, your tool needs sharpening. If that doesn't work, you need more practice.

    Frank
     
  15. George Foweraker

    George Foweraker

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    I turn everything at the fastest speed i feel is safe.
    I turn the speed up until i start to get some shake then turn it down until i lose it.
    As the piece comes into balance i gradualy turn the speed up.
    If you are turning until screws start to loosen you are heading for a fall.

    george.
     
  16. LHauch

    LHauch

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    To quote Bill Grumbine (from one of his great videos which I highly recommend for people wanting to learn to turn bowls http://www.wonderfulwood.com/)

    "If the lathe's not shaken and your not shaken, you're turning at the right speed."

    Works for me, as I developed better tool techniques and confidence, I started turning the speed up on the lathe. It probably to 6 months for me to be comfortable with finishing a 10" dia. bowl turning at just under 1500 RPM. Depending on how well the blank is balanced, I start between 250 and 500 PRM on bowl that size. As I true it up, the speed goes up.

    Now, after about 3 years, I don't look at the speed, except at the very beginning (don't want to turn a winged bowl at spindle speeds.)

    Cheers,
     

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