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NR Scraper Turn Speed?

Discussion in 'Woodturning Discussion Forum' started by Randy Anderson, Aug 9, 2020.

  1. Randy Anderson

    Randy Anderson

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    I'm a heavy user of my NR scrapers. For us mere mortals even our best work with a gouge will have a tool mark or compression mark here or there and a good NR scraper and time are much more interesting than 80 grit paper. I know the basics - good bur, light touch, even movements, sharpen often, etc. I'm still not settled on the right speed and maybe it's a big "it depends" answer. On natural edge green bowls I try to keep it slow to avoid warping of the tall wings while spinning. 450rpm seems to be a good speed to start at and see if gets a good finish. Lots of variables on those - wood movement, wall thickness, balance, etc. On dry bowls I sometimes can still get chatter marks and wonder if it's too much pressure on the cut or speed, or a combination. It "feels" better at slower speeds, still in the 450-500 range but does that impact the life of my edge? Just curious of some general rules of thumb that would help. I know in general with gouges that faster is better but...
     
  2. john lucas

    john lucas AAW Forum Expert

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    If your getting chatter it's too much pressure. Takes.a.super light cut on the wings.
     
  3. Richard Coers

    Richard Coers

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    The bowl size must enter the discussion if you want to talk about speed.
     
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  4. Roger Wiegand

    Roger Wiegand

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    For her 3-4" pieces Cindy Drozda runs at ~2500 rpm (top speed on her lathe) in the demos I've watched. She starts sanding at something absurd like 600 grit after the NRS. That would be the equivalent rim speed of 800-1000 for a 10" piece, but I have the impression she'd go faster if her lathe did. I haven't seen her turn a big piece.
     
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  5. Randy Anderson

    Randy Anderson

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    Wow, that's fast. Don't think I want to try and spin a 13" bowl that fast. Not really looking for a set speed for NR scraping but rather does faster or slower produce better outcomes in general. I've seen people do both - scrape at turning speed and others specifically say slow down a lot for NR scraping. I do believe my chatter is more about my impatience with that last tool mark that just won't come out so I subconsciously (or on purpose) press harder than I should. Depending on the wood it is cool when after a bit of time with a scraper you hate to even put sandpaper to it.
     
  6. Robert D Evans

    Robert D Evans

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    I find that faster generally creates smoother cuts.
     
  7. odie

    odie

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    I have a theory that each lathe has a certain threshold of inherent vibration, and when you spin one particular piece of wood, the vibration may be slightly different than the same piece of wood on a different lathe. The wood block and the lathe each contribute to the vibration intensities that are possible. As you turn, the vibration may be altered. (It usually gets better or stays the same, but there are times where the vibrations are exacerbated.

    As Robert suggests, faster usually produces a cleaner cut, but there is a point where adding rpm does not produce a better cut. IMHO, it's also important to refine the rpm to produce the least vibration possible. No detectable vibration is great, but sometimes the least possible vibration is the best workable speed.

    There are other variables, such as sharpness, tool choice, presentation......and an individual's personal technique, that all enter into the overall quest for the cleanest cut possible. :D

    -----odie-----
     
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  8. john lucas

    john lucas AAW Forum Expert

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    The only reason speed.produces a finer cut is the tool.is taking a shallower cut. People have a tendency to push any tool.faster than it wants to cut. With scrapers.its more.about pushing the tool deeper since you dont have a bevel to control the cut. With interrupted cuts like a natural.edge.bowl it's too easy for the tool.to.be pushed too deep. Increasing the speed reduces the time a tool.can fall.onto that gap so you have less bounce. The better your tool.control the less this is a problem. I would suggest simply doing a test.
     
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  9. hockenbery

    hockenbery AAW Advisor Staff Member

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    That’s the key element. with the scraper it is edge contact pressure not the bevel pressure. Edge contact pressure can be more difficult to control. Mastering the bevel presser with the gouge will help.

    Floating the bevel on air and wood is the most difficult task in turning.
    Master turners do this well at most any reasonable speed.

    Less experienced turners tend to cut too fast across the interrupted cut area because they are subconsciously afraid of cutting there and want to get through it.
    The higher speed allows both a faster feed rate and less time for the tool to cut deeper into the air than the wood.
    The key is learning to float the bevel on the air at the same depth you were on the wood.
     
    Last edited: Aug 10, 2020
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  10. robo hippy

    robo hippy

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    I keep the lathe at the same speed I use for turning when using the NRS. I use them more on boxes than I do on bowls, except for sweeping across the bottom of a bowl. Generally I prefer a shear scrape for cleaning up the sides of a bowl. It depends on the wood more than anything else.

    robo hippy
     
  11. Brandon Sloan

    Brandon Sloan

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    For me it all comes down to tool control. The speed of the lathe needs to match my tool control. It’s a balancing act. I see no benefit to turning something at high speed, if I can’t keep up on my end. Same as turning at slow speeds, if I’m too fast with the tool, results will suffer. After watching as many turning videos as possible, I’ve come to this conclusion. The tool is going to do its job and cut the wood. The lathe is gonna do its job and spin the wood. The rest is up to me. It’s good to ask these types of questions because you get an idea of what some damn good turners are doing. Using what you learn from others will really help you find what works best for you.
     
  12. john lucas

    john lucas AAW Forum Expert

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    One of the best sentences ever Brandon.
     
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  13. Brandon Sloan

    Brandon Sloan

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    Thank you Mr. Lucas, you just made my day.
     
  14. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    In my experience, NRS does not work on all woods. I can leave a glossy finish in some, but it will tear the heck out of Koa. You have to re-cut it with a gouge. I like a rather fast speed for the NRS. Within reason of course.
     
  15. robo hippy

    robo hippy

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    Brandon, that is an excellent quote. Where is the T Shirt?????

    robo hippy
     
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  16. Brandon Sloan

    Brandon Sloan

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    I’ll send you one!
     

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