Speed, torque, cut, scrape?

Discussion in 'Newbie' started by Regis Galbach, May 28, 2017.

  1. Regis Galbach

    Regis Galbach

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    Now that I'm starting to do things larger than pens, lathe speed becomes more of an issue. I turned pens at 2800-3300rpm. Certainly not suitable for 6" bowl.
    My lathe (1221VS) has 3 belt positions where I could actually turn 900rpm or less in all 3 belt positions.

    Therefore, my question is should I use the most torque for the speed that I am cutting with? Does it matter?

    When doing pens, I stayed at the highest speed position and cut about 3000rpm and applied CA at about 250rpm. Should I turn & finish a 6" bowl at 900-100rpm?

    Related question is should I cut and scrape at the same speed (for same size item)?

    I'd like to learn as much about turning speed as experienced turners will offer/share.

    Thank you,
    Regis
     
  2. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Use the low speed range where the lathe will have the most power because you really do need the extra power. On lathes with electronic speed control, whether AC or DC, the power is proportional to motor speed. With the belt in the low speed range, the motor will be running at the highest speed while the spindle will be turning at a rate appropriate for bowl turning. I rarely turn bowl size pieces faster than 800 RPM.

    If you read Road & Track you know they love to talk about torque, but really it's power that does the work ... torque is for tightening bolt heads ... or winching a four wheel drive truck out of the mud and back onto the pavement where it belongs. :D
     
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  3. hockenbery

    hockenbery AAW Advisor Staff Member

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    Ditto on the low speed range.
    In addition to more torque you have fine granularity in speed control.
    I have the same lathe and speed range doubles with each pulley step
    60-900 120-1800 240-3600

    On the 60-900 A 1/10 of a turn of dial is 84 rpm
    On the 240-3600 a 1/10 of a turn is 336 rpm

    the finer control with the 60-900 belt really helps in eliminating vibration.
    When roughing I set my speed just under the spot where the lathe begins to vibrate too much.
    With an out of balance piece the lathe will vibrate a little regardless but you don't want the lathe on the verge of moving around.

    When I use my big Oneway. It has plenty of power on the middle belt but I go to the lower belt on large out of round pieces to get the finer control of speed.

    I like to sand with the bowl in the 200-300 rpm range maybe slower.

    Finally when you are starting out slower speeds are better. At higher speeds bad things to happen faster (and maybe more often) with more damage to the work or the turner.
     
    Last edited: May 28, 2017
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  4. robo hippy

    robo hippy

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    I guess I could add that power needed depends on how you turn, and how big your tools are. As a production turner (retired from that now) I need a big lathe and big tools. For a mini lathe, So, bigger tools tend to take more power when cutting. If you are going easy on your cutting, and your tools are sharp, then you don't need the big tools. 3/8 inch gouge, and 1 inch wide scraper max. If you try to take off too much in one pass, or get too much steel into the wood at one time, then that is when you stall the lathe, and/or have catches. I do scrape (far more than most people), and do that at the same speeds that I do when I cut with gouges. I do have a bunch of bowl turning videos up on You Tube. Just type in my alias...

    robo hippy
     
  5. odie

    odie

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    I turn all of my bowls at the 1200 rpm belt setting. The actual speed I'll turn any individual bowl is solely dependent on the highest speed within this speed range that produces the least vibration.....I've found this speed to be where the finest cut will be had. I'd guess the average speed I turn bowls at is somewhere around 800-1000 rpm......but, if I can get vibration free at 1200 rpm, I'll use it.....because speed is a factor (but not the only factor) in producing finer cuts. This is very similar to swiping a sharp knife at a piece of paper. You can swipe the knife slowly, and you won't slice the paper very cleanly, even though the knife edge is sharp......but, if you swipe fast, the knife will slice the paper very cleanly. The same principle applies to woodturning......up to a point. There is a speed you can turn at that will yield a good clean cut, and increasing the speed won't produce a cleaner cut......provided vibration doesn't factor into this. A vibration free rpm is the better part of the equation when searching for clean cuts, than speed is.

    For a rank newbie, I would suggest heeding some advice you're getting from Al and Bill......and slow it down a bit less than the speeds I turn at. This is strictly for safety reasons. A new bowl turner is bound to get some fairly large catches......up until that point where he's getting some sense of what can and can't be done with the presentation of gouges and scrapers. A big catch can be dangerous.......and, adding speed will increase the danger! :eek:

    -----odie-----
     
    Last edited: May 31, 2017
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  6. John Torchick

    John Torchick

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    Thanks for the inquiry and thanks for the advice. I'm turning pens and want to move on to small bowls or platters. Makes sense to monitor speed, piece size and vibration.
     
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  7. Regis Galbach

    Regis Galbach

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    Thanks for all the tips. When I watched robo-hippy's scraper video I almost wanted to through out my gouges...LOL
    I will use lowest range and keep it slow for now and will hopefully I'll remember odie's comment about once finding speed that cuts clean, faster won't help.

    Thank you all,
    Regis
     
  8. Vern Crandell

    Vern Crandell

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    Another thing to remember is, the larger the piece, the slower it should spin. The general rule of thumb is diameter of the piece times rpm should be in the 6000 to 9000 range (maximum). For your six inch bowl 1500 rpm would be the maximum. Remember this also depends on if the piece is balanced, sound (no cracks, splits, etc.) and your experience. Slower is always better if bad things are going to happen.
     
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  9. Regis Galbach

    Regis Galbach

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    Now, that sounds like feed/speed on a metal lathe. Thought there would be something like that but, wasn't sure

    Thank you,
    Regis
     
  10. Bill Boehme

    Bill Boehme Administrator Staff Member

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    This is a rule of thumb that Craft Supplies puts in their catalog , but sometimes it's incorrectly interpreted as minimum and maximum values ... using the six inch bowl for example and mistakenly thinking that the optimum speed should be between 1000 and 1500 RPM. I think that a better way to visualize the rule of thumb is to think of the lower number as the beginning of the red danger zone on a tachometer and the higher number is the "never exceed or bad things will happen" speed. I would want to start a six inch bowl at no faster than 50% of the smaller number ... which would be no faster than 500 RPM. If the wood is out of balance then maybe 25% or 250 RPM.
     
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  11. Mike Johnson

    Mike Johnson

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    Depending on the lathe the turner is using will many times determine the lowest speed to start at.
    Many of the budget priced lathes do not have slow enough speeds on the low end when roughing
    out blanks or turning larger pieces. This can create hazards for the beginning wood turner when they
    don't have the experience to identify a bad situation waiting to happen. I have watched a number of
    video's on the internet of wood turners roughing out blanks at too high of speeds or blanks that were
    extremely out of balance. Many of the reeves drive lathes will slowly turn at higher speeds as the reeves
    pulleys become dirty and gummed up. These can be a hazard unless you stop and clean the reeves pulleys
    and shafts so they work properly. Another valid reason to use a VFD for speed control.
     
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  12. john lucas

    john lucas

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    Bill and Vern have given you a ball park idea of speed ranges. For roughing start about as slow as your lathe will go and if it's too slow (think thunk thunk thunk) then speed it up a little and find a speed where your comfortable. As it gets round you can increase the speed but the speed ranges Vern gave are a good reference point. Always, always listen. If you hear anything unusual stop the lathe and figure out what it is. Cracks can be there, especially for new turners who aren't used to looking for them. A bowl spun too fast and you get a catch can blow up easily due to an unforseen crack. Although it is true that you do get finer cuts when the wood is spinning faster you can easily get a very good bowl at a very slow speed. It's just a matter of not forcing the tool to cut. Much safer to turn slow and not get hurt than to turn fast thinking you'll get a better cut and then get killed. For a very long time I never turned over 1200 rpm. Just didn't think I needed to. Patience and learning how tools work and you can turn anything at that speed or slower. As you get experience of course you can turn pens and small boxes at much higher speeds.
     
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  13. Hy Tran

    Hy Tran

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    In metalworking, in general, there is something of a sweet spot in terms of speed-of-tool-relative-to-workpiece (surface feet per minute for those of you still using customary units). In wood, the sweet spot is huge (you can get clean cuts without excessive wear on the tool over a very large range of speeds), so as the others here have stated, safety is of prime importance--because it's the wood being brought to the tool, rather than the tool being brought to the wood.

    For finish scraping (to remove the feed marks from the gouge), I like dialing up the speed (nice kiln-dried stable wood), and I take the lightest cut possible, moving the tool slowly (as slowly as I can move smoothly, basically).

    What everyone else said about roughing cuts and initial rounding. If your tool bounces, you are not controlling the cut. Rethink which way the wood is going, and how would you do a cut so you don't have an interrupted cut (or minimize interrupted cutting).

    Blanks that have been pre-cut to "pretty round" are easier to work with.

    Have fun!
     
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