Taking fine cuts inside a bowl...

Discussion in 'Newbie' started by Jamie Straw, May 31, 2016.

  1. Mike Johnson

    Mike Johnson

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    What happens if you forget to take light cuts with the bowl gouge at higher speeds. :eek:
    I usually take a break and sharpen the tool and start fresh when make finishing cuts, otherwise you can get in a hurry and end up with a tool catch.
    Most mistakes happen when you spend too much time during a turning session and try to push the project along too fast.
    Most of the time when I get in a hurry I end up having to spend more time fixing the mistakes from loosing focus or attempting a short cut.
    No fun putting long hours into a piece and messing it up when you are close to the finishing process!
     
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  2. odie

    odie

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    Howdy Breck.......

    Thinking of the process as 2-step is a good way to understand it. I do have a question for you, though......If the increased speed makes the gouge flow smoothy during the second step, why not use the increased speed for the first step, as well?
     
  3. hockenbery

    hockenbery AAW Advisor Staff Member

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    Speed is a trade off.
    Faster speed generally makes for a better cut.
    Faster speed makes more vibration and more vibration makes for a poorer cut.
    I generally adjust the speed up to an acceptable vibration. Once it is round the vibration Decreases and the speed can be increased.

    Vibration is a function speed, size of the piece, the amount of warp, How well the grain is balanced,density balance of the wood, and how well the bowl was lined up for re-turning.
    With a smaller bowl up to 10" or so you can probably go full speed without vibration.
    With a 15" bowl you might have to go a 1/3 of the speed you would with the 10" bowl until it gets round.
    A poorly lined up bowl will require a slower speed than one that is lined up well.
     
    Last edited: Aug 4, 2016
  4. robo hippy

    robo hippy

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    I prefer to turn at higher speeds. It doesn't make for a better cut, but it does make cutting easier/smoother. I think for me, the slower speeds are slow enough that my thought train stalls where faster speeds keeps the concentration in line, if that makes any sense. You get more cuts per inch than at slower speeds....

    I have always wondered at how much wood elasticity plays into vibration.... Dry wood, not as much, but wet wood a lot, especially as your speed goes up. With grain orientation, especially with high speeds and thin walls, the bowl will elongate along the grain, and shorten up cross grain, pretty much in the same way it warps as it dries. Probably a big part of why green pieces go oval as you turn.

    robo hippy
     
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  5. Breck Whitworth

    Breck Whitworth

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    When I said to think of the final turning as two stages that is a method I use with students or those who are not real experienced turners. The main reason is to get them used to resharpening their gouges before their final finish cuts. The extra speed is more of a mental thing for newbies because a little extra speed seems to put them out of their comfort zone just a hair. I have found they will then concentrate a little more on rubbing the bevel before tilting the gouge into the wood for smaller shavings. Also it seems to help them to remember not have a death grip on the gouge. For me the speed doesn't really need to increase because I am comfortable with the higher speeds. Being a little more cautious before allowing the gouge to bite into the wood seems to help my students. Being an old teacher I use whatever works until I find something better. I have found that there are many different ways to do things and get good results, so try stuff until you find what works for you.
     
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  6. odie

    odie

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    Thanks for the clarification, Breck.......I get it! :)

    Great food for thought here in this thread.......! :cool:

    As I see it, there are two reasons one might slow down the rpm......out of balance, and harmonic vibrations caused by general shape compounded by thin walls. There isn't much you can do for out of balance, but slow down until it's gone. For the harmonic vibrations, I've found the Oneway bowl steady to be a great help to me.

    As for size of the workpiece, Al......Yes, I can agree that size is a factor, particularly for very large bowls...... but bowls that are smaller can also have both out of balance, and harmonic vibrations......either, of which can be contributing factors.

    Robo.......I think your word "elasticity", and my words "harmonic vibrations" are referring to the same thing. I think you are absolutely right that, if you can, a higher speed is more desirable than lower speeds, particularly during the final few cuts prior to sanding. This is where I've found the Oneway bowl steady to be applicable to the results possible. It's not a "silver bullet", but it is a help......the rest is up to you!
     
  7. hockenbery

    hockenbery AAW Advisor Staff Member

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    Small things can vibrate for sure.
    Lathe size is also a factor. An out of round bowl will vibrate more on a lighter lathe than it will on a heavy lathe.
    A small bowl might vibrate a lot on a100 pound midi lathe and not at all on an 800 pound Oneay.
     
  8. odie

    odie

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    True for an out of balance condition, but not necessarily true for harmonic vibrations. In the case of the latter, it's strictly a matter of tool application, geometry, integrity of a specific piece of wood, and wall thickness. The weight of the lathe is less of a factor for this kind of vibration than it is for an out of balance condition. There are ways to successfully deal with it.
     
  9. hockenbery

    hockenbery AAW Advisor Staff Member

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    I would think vibration from tools is likely to be more with a lighter lathe.
    When you get those vibrations from the tool use you just have to back off what you are doing.
    Sharpen the tools, take lighter cuts, use less bevel pressure, keep thicker supporting wood toward the Chuck or faceplate.
    Taking the 1/128" cut with a gouge takes a lot of practice.
    Beginners get the 1/4" cut and the 1/8" cut pretty quickly.
    Mastering the thouch to make the light cuts take a while.

    The good news is that people who don't have finesse with the tools can still do really nice pieces.
     
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  10. Zach LaPerriere

    Zach LaPerriere

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    Hi Al,

    That's definitely something to work toward! Can I ask a few of questions?

    1. How much cleaner do you think consecutive micro cuts gets the interior of the bowl? In my experience so far, a couple 1/32 cuts on difficult grain is about as clean as it gets for me. I've tried finer and haven't noticed a difference, but I'm at best an intermediate turner on a good day.

    2. You mentioned the Michaelsen grind as good for the first couple of inches. I'm a big fan, though I usually use a 3/8 or 1/2" with a Michaelsen grind. I prefer the flute-up cut with the Michaelsen grind once past the rim.
    Do you have a favorite gouge or cut for the rest of the interior, both the curve further in and the bottom? On steeper curves of course the flute-up doesn't work very far in, and I find micro cuts more difficult when rolling the flute clockwise. I find an Ellsworth grind best for flat bottoms.

    Thanks!
    Zach
     
  11. robo hippy

    robo hippy

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    I will not use the flute up cut. Mostly it is prone to catching because if you come off the bevel even the smallest bit, you have a scraper pointing up into the spinning wood. I prefer more open fluted gouges, like Doug Thompson's fluteless gouge, and roll it over almost vertical for a higher shear angle, and hold the tool almost level. If it comes off the bevel, you have a shear scrape. 70 degree bevel, relieved heel, and ) nose profile. I am different that way. I don't use the swept back gouges at all, mostly because they work better with a dropped handle and you cut more with the wing than the center of the nose.

    robo hippy
     
  12. hockenbery

    hockenbery AAW Advisor Staff Member

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    I don't use scrapers inside bowl very often. On about a third of the crotch bowls I do I have to use a scraper on the bottom because the twisty grain will get lifted up by the shear cut. The edge of the gouge slips under the grain stead of cutting it. Just the nature of how the edge meet the fiber. A round nose scraper removes the last little bit of wood when this happens.
    On a very few deep cut rim bowls I will have some difficulty keeping the bevel and get a hint of chatter and USA a scraper to clean it up. I switch to the scraper when I have enough wood left to scrape and not enough to fail again with the gouge and scrape.

    What I strive for with the gouge cut is to be able to sand with 220. Most of the time I can sand 90% of the surface of hollow forms and NE bowls starting with 220'once they have dried for a few days. There are usually a few spots where I use 180 especially a transition line where I have not been able to match the two surfaces more than a 1/3 of the way around. On cut rim bowls I usually start sanding with 180 unless I have turned beads or other details which I sand at 220 or 320 depending on how they look. With a 1/32 cut you should be able to start sanding with 180 or 120.

    Small bowls are easier than large. I returned a 10" hard maple bowl recently used only the Ellsworth except for turning inside the foot where I used spindle gouge some. This bowl was easily sanded with 220. Probably 320 in spots. Of course hard maple is a wood the cuts cleanly easily.


    I use the Ellsworth almost exclusively on the inside of bowls. Don't do many steep walls and I like a curve to make the flute up shear cut work. I do do a few NE hollow form openings that are close to straight.

    . Reed,
    The flute up shear cut is best learned in a hands in session.
    Anyone trying to learn without help is likely to get lots of big catches especially if they hold the tool too tightly. When teaching ourselves we all have a natural tendency to tense up when we Are apprehensive.
    The Ellsworth grind on a parabolic fluted gouge works really well. People that learn the shear cut don't get catches because the tool does not roll into the wood once the bevel is locked in it just follows the curve.

    I encourage people to learn the flute up shear cut in handsome on. It is not a safe cut for people to learn on their own.

    Al
     
    Last edited: Aug 11, 2016
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  13. hockenbery

    hockenbery AAW Advisor Staff Member

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    @Zach LaPerriere
    A tool I use a tiny bit is a finishing gouge Trent Bosch introduced me to.
    He used a 3/8 bowl gouge for flute up finishing cuts inside and out by grinding the two sides differently.

    image.jpeg
    The right side is a traditional grind the left side is swept back with a very short wing.

    The right side is used flute up on the outside of the bowl cutting foot to rim with the bowl jamb chucked so that it makes a near verticle slicing cut.

    On the inside it makes a flute up shear cut similar to the Ellsworth.
    The leading edge of the left side is bit more vertical than the Ellsworth leading edge.
    I have one somewhere in the shop but since I do mostly hollow forms and natural edge bowls don't use Trent's tool for the few cut rim bowls I do each year. Also my little Michelson does as well if I need it.

    You may not want an extra tool,
    However anyone doing production bowls might consider it.

    A weekend workshop with Trent has changed a lot of lives.
     
    Last edited: Aug 11, 2016
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  14. robo hippy

    robo hippy

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    Al, the above gouges look to me like SRG's (spindle roughing gouge). The flute shape is identical. To me, the safety point is the part of the gouge that is doing the cutting should be directly over the tool rest, so all of the force of the cut goes down into the tool rest. This keeps the tool 'balanced'. With the flutes pointing straight up, you are working one side of the teeter-totter/seesaw, and it wants to roll into the cut. Roll it onto its side, and cut with the bottom 1/3 of the tool, and you have a balanced cut that will not catch, even if you come off the bevel. You still get the high shear angle for a clean cut.

    I am playing around with the NRS (negative rake scraper) for bowls. I never have used a scraper flat on the tool rest for that bottom sweep to take out the ripples or for clean up. The NRS works in some of the harder woods, but I still find the shear scrape to cut cleaner most of the time. When you sweep across the grain with a scraper, like across the bottom of a bowl, it will cut more cleanly than it will when you are plunging down through the grain like going down the side of a bowl. I still like a 70 degree or so shear cut or shear scrape for my bottom finish cuts.

    robo hippy
     
  15. hockenbery

    hockenbery AAW Advisor Staff Member

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    Big difference from an SRG.
    Trent's finishing tool is a 3/8 bowl gouge made from a round bar with a flute cut in it.
    A "u" fluted bowl gouge can look like an SRG at some level of abstraction but the steel is thicker
    And being milled from a round bar the bowl gouge is much stronger than the typical SRG.

    The smallest SRG I KNOW OF IS 3/4" and most are 1 or. 1.25"
    Most are made from a flat bar that is bent into a flute after a tang is cut in the bar.
    SRG is too big and too weak to use on bowls.

    A catch with a 3/8 bowl gouge can be bad but it is sort of limited to gouging out a 3/8 diameter chunck of wood.
    An SRG gouging out a 3/4" or 1.25" chunk of wood is many times more dangerous.
     
    Last edited: Aug 12, 2016
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  16. Zach LaPerriere

    Zach LaPerriere

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    Al—

    Thank you very much for your detailed response. My apologies for a late response...I was out commercial fishing for a bit over a week, far from the internet, land, and my lathe.

    I would feel like I'd gone strait to heaven if I could consistently begin sanding the inside of bowls at 220. I know a lot of my courser grits is the nature of the soft woods here in Alaska, but I know my skills aren't what I would like them to be.

    I've been paying attention that you've mentioned a course with Trent twice now. Seems like a great thing to do this Fall.

    Trent's finish gouge makes good sense to me. I'm a huge fan of sheer cutting the exterior of the bowl on finish cuts, and that is essentially what it looks like his finish gouge is up to, especially where it's most needed on the interior.

    Anything to save on courser grit sanding time, short of selling my soul or importing wood!

    Best,
    Zach
     

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