Holding green blank without tenon

Discussion in 'Newbie' started by Jamie Straw, Jul 29, 2016.

  1. Jamie Straw

    Jamie Straw

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    A few of these pieces of Black Locust are best suited to become something very shallow. I'm not keen on internal (expanding) holding with a chuck, haven't tried it yet, though I now have a Nova chuck that has a dovetail profile. Is there another way to hold a fairly green blank for turning? Any glue+glue-block option?
     
  2. Gerald Lawrence

    Gerald Lawrence

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    I use SN2s and mostly use compression on my tenon, wet or dry. I do sometimes use expansion for platters and some other turning in wood that is not very fresh so you could say partly dry.
     
  3. john lucas

    john lucas

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    Expanding into a recess is a very good way to hold wood as long as you leave enough wood outside the rebate to keep from cracking the wood due to the internal forces. If you make the opening just barely larger than the jaws fully closed you get a very good grip and it won't mar the opening so you can leave it. I do most of my platters this way.
    CA glue will glue a glue block to green wood. Don't use the accelorator for a stronger bond and use medium or thick. You have to flatten both surfaces so they meet perfectly flush. The thick CA will compensate somewhat for a not perfect fit.
     
  4. hockenbery

    hockenbery AAW Advisor Staff Member

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    IMHO using an expanding hold on a small NE bowl will ruin any chance at a decent looking bowl.
    You need extra thickness on the bottom for the Chuck. And you have a 3" hole that cannot be incorporated into a decent look for 9" bowl.

    A couple of options I use.

    1. Use larger jaws #3 and plan the outside of the bowl to be inside the tenon. If you have a 1/2" tenon and plan an 1/8" wall thickness the inside hollowing can be below the top of the tenon an 1/8". When you reverse Chuck carefully follow the inside curve on the outside. This is an extra challenge turning blind to match the curve. But it isn't that hard once you have done it a few times.

    2. Use a glue block with thick CA. CA will bind wet wood to a dry glue block for an hour or two. Wood movement will break the glue joint so you have to finish the turning in 30-40 minutes. I use a 3" diameter glue block on a small faceplate turned from dry wood with a slight concave in the glue face and a 1/8" hole in the middle. I rough turn the outside of the bowl between centers with no pin in the tailstock center and make a slight concave on the bottom 3.25"-3.5" diameter. I chisel away the little bump under the tail center and mark the bottom center of the bowl with a pencil point. Make a dimple at the center mark by twisting a drill bit in your fingers. I use a straight piece of coat hanger wire through the hole in the glue block with its end in the little dimple to line up the glue block. Draw a pencil,circle around the glue block. Run two beads of thick CA inside the circle. Spray accelerator on the glue block. With the wire in the dimple slide the glue block down the wire and twist it just as it makes contact with the wood. The twist is critical! The twist spreads out the two beads of glue toward the center in a wide glue surface because you have the two concave surfaces meeting at the edge of the glue block. I mount the bowl on the lathe, finish turn the outside hollow the bowl,using the tailstock until it is in the way. To remove the bowl I put a flat chisel in the glue joint and tap it with a mallet. The CA GLUE fractures with usually with no damage to either wood surface. Once in a while a fiber might get pulled out requiring a tiny bit of turning when the bowl is reverse chucked to finish the bottom. With this hold all but the 1/16" of wood turned away for the glue recess can be in the bowl. Amazingly this glue block technique is almost as fast as using a Chuck. Turn the glue off the glue block and it is ready to go again. The glue blocks last for hundreds of bowl if you just remove the glue and no wood.
    Also if the bowl is shallow and you are making a round footless bottom you can blend the area under the glue block into the turned surface by sanding.

    3. If you are no longer getting catches a 1/8" tenon with a dovetail jaws will do the job provided you use the tailstock support for the initial hollowing. I am doing this a lot with the NE bowls I turn from crotches. They will have round bottoms with no foot so the edge of the #2 tennon is turned into the bottom surface.

    Al
     
    Last edited: Jul 30, 2016
  5. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I don't like expanding into a mortise and especially if the block is shallow because I would want to turn away the ugly mortise and make a nice looking foot. I guess it's just me but having a bowl with a mortise on the bottom just looks like the piece hasn't been finished yet. Either turn a short tenon or use a glue block.

    How thick is the wood that you say is shallow? My concept of shallow would be less than 1.5".
     
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  6. Jamie Straw

    Jamie Straw

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    I'm supposed to be at dinner, but had to be a smarta$$ for a moment. I've gotten only one catch so far on a bowl, and that was with a scraper and not too bad. I feel safe publicly stating this tonight, because with the 1236 disassembled as it is, I won't be turning any bowls for a day or two.:D:D:D

    Appreciate all responses, just been stuck in broken tool land and not responding.
     
  7. MichaelMouse

    MichaelMouse

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    Absolutely. You have a few pieces of misinformation to dispose of before you do, however. First, a recess will ALWAYS give a deeper bowl than a tenon with heart up. More or less even with heart down, provided you intend to leave the tenon as a feature. If not, depth favors the mortise.
    [​IMG]
    The narrowest part of each is 2" to scale. In reality, you'd want to make the tenon nearly 2 1/4" to account for recircularity after shrink. Second, you automatically get more wood around a mortise, so unless you think the hold must "grip" rather than snug in place, and you crank too much into the chuck, lifting up the thinnest part with the wedge, use it. Fit it properly, as in the examples shown here.

    [​IMG]

    Note the corrosion images.

    Now, time to be smart and not willy-nilly hang a 40 pound hunk of wet wood. Turn between centers until you're at your most balanced and lightest, and check periodically for SNUG, NO MORE if things seem to make noise or wander. I use a pin chuck, but pin jaws - longer the better and BOTTOMED for alignment, like the dovetail jaws - a woodworm screw, properly shouldered by the jaws surrounding it, or a faceplate also work fine.

    I can do, though I don't make it a practice, a 16X9 throwing more water than the picture above on a 2" mortise, and I'm nothing special, just a cutter versus a scraper, so to reduce resistance on the passage of the tool.

    [​IMG]

    Sixteen X 7 or so.
     
  8. hockenbery

    hockenbery AAW Advisor Staff Member

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    @MichaelMouse has missed that we were discussing smaller natural edge bowls.

    The recess takes away so many design options. First the bowl has to be thick walled with a wide foot to accommodate the recess. The big hole in the bottom just doesn't fit with design options I want Availble to choose among when I turn a natural edge bowl.
    Below is a diagram of the recess. If you use a 3/8 deep recess you can't have 1/4 walls in your bowl. And a 3 inch hole makes the bowl too dumpy looking for my taste.

    image.jpeg

    With a tenon you have the option of a round footless bowl which I prefer for natural edge bowls.
    You can also make a foot any size smaller than the tenon. The bowl does not have to look dumpy.
    Below is a diagram showing using all the wood with tenon. Of course you have to turn away the tenon when you reverse Chuck the bowl to shape the small foot shown.

    image.jpeg
     
    Last edited: Aug 1, 2016
  9. robo hippy

    robo hippy

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    Al, the way to escape that extra thick bottom is to turn a small concave shape off the foot to meet up with the inside wall thickness. I guess it would be half of an ogee, so on your drawing, about a 1/8 to 3/16 radius which would match the 3/8 deep recess and wall thickness. 3/8 is way too much of a recess, 1/4 is over kill, and 1/8 is fine for almost all applications, even on green wood.

    robo hippy
     
  10. hockenbery

    hockenbery AAW Advisor Staff Member

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    Reed,
    That works, I can turn away the edge of the recess which is a good thing to do, and I can make the bottom curve to a small foot but I have lost more wood than I would have had I used a tenon.
    In addition it is much easier for me to visualize the finished bowl using a tenon than it is with a recess.

    Basically if the goal is a small foot or no foot a 2-3" recess does not get you there in an efficient way and wood is turned away for the recess that isn't turned away when using a tenon.

    It is my opinion the average turner is going to break an 1/8" recess much more often than they will break an 1/8" tenon.

    Recesses are good for lots of things. They don't work well for me on small natural edge bowls
     
  11. MichaelMouse

    MichaelMouse

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    Nope, unless you have some fetish about all points being equal thickness, it's perfectly possible to have the recess only an eighth or so, while the curve to the recess is a quarter or so. Not a convincing explanation there.

    No limit to curvature elsewhere, either.

    [​IMG]

    From candy dish to full centerpiece, anything is possible.

    [​IMG]

    Sorry, both are unnatural edges. Here's a natural.

    [​IMG]

    Just for you, a "foot" fo a little lift. You should get some practice.
     
  12. hockenbery

    hockenbery AAW Advisor Staff Member

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    @MichaelMouse
    Your photo proves the point. You end up with a 3" diameter foot. It works well for the large bowl in your photo.

    You know by now the discussion is about small bowls so assuming you are not just being a troll I'll try one more time.

    The discussion is about small NE bowls where the 3" foot is way out of proportion.

    It comes down to what we perceive as esthetics If you like a 3" foot an everything regardless of size that is your choice.
    As long as the 3" hole for the recess is part of the design it works.

    I like a smaller foot on smaller bowls or no foot which is my favorite especially for larger functional natural edge bowls.
     
    Last edited: Aug 1, 2016
  13. Gerald Lawrence

    Gerald Lawrence

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    Another way to handle the compression tenon is to have no foot at all and have a calabash style (rounded top to bottom) . This I have recently started doing and it works very well for 7 inch and smaller NE bowls. Sorry no pics, gave the first ones away and the last is in finishing stages.
     
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  14. MichaelMouse

    MichaelMouse

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    Can't see the difference in the diagrams, where you have to start your bowl tenon shoulder above the edge of the mortise, I perceive. "Just for you," I include a a demonstration of a mortise inside a tenon, to show that your contention that you can't go thin and bark up in the same piece, and you still don't get it. BTW, 2" plus maybe a quarter larger each size for the "foot" makes 2 1/2. You want to argue style, I want to present substance. Can't help YOU, possibly influence others to think creatively and not fear a perfectly useful concept. The open mortise no-foot form sitting on its 2" (or other) base is also my preferred way of conveying lift. It's just that I like to have folks use the bowl or plate rather than chase it.

    You know there are 1" dovetail jaws, or do you? If you're working small, they do a nice job of staying small. The little dark maple wood chip dish was ~6" long and maybe 2 wide with a 1" recess. As a matter of taste or style, you use what's appropriate to your objective, though sometimes it looked better in your mind than on the table. This is a bit over 10 with an inch and a quarter base. Obviously there's an inch or more of thickness on the bottom to keep it from tipping over. Now if only it had looked as good in person....

    [​IMG]

    In any case, newbies, remember that a set of dovetail jaws give you an excellent hold when you realize that they don't "grip" anything, just wedge the nose up against the bottom of the mortise as they expand. I believe the key to use of ANY hold, innie or outie, in maintaining circularity and position throughout, is to use support from the tailstock for as long as possible. Also safer, because even a horrible "catch" won't send the piece up into whichever portion of your anatomy you may have in the way. Which, incidentally, can oly happen if you are UNDER the wood. Cut above center on convex, below center on cncave surfaces, and there will be air there. Use the gouge properly, like this (c and it cannot catch, right Jamie?

    If you have a Nova chuck and just HAVE to have an external hold, I suggest the "75mm" set, which are actually larger in outside diameter, but can hold a 1.8 inch spigot or 1.3" (standard 2X) square.
     
  15. MichaelMouse

    MichaelMouse

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    If you're doing a tippy container, makes perfect sense. Doesn't hold much securely, though. I have made some "sets" with round bottoms resting in through holes in bases. See the board dish above, and imagine cutting the central area thin enough to see the jaws in the mortise underneath. Knife and sandpaper make a finish for a circle to rest the dish in. Carry one more step, cutting a groove the size of the base hole, and they can go catty-whompus or put the firm opening up by fitting the groove into the hole to prevent tilt.

    NB: At lakeside shows, keep them calabashes contained where they can't roll off the shelf under wind pressure.
     
  16. hockenbery

    hockenbery AAW Advisor Staff Member

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    1. @Gerald Lawrence
      I also do round bottoms on most of my NE bowl and hollow forms. Mine are not as ellegant as the calabash shape. Surprisingly the round bottoms add a lot of functionality to the bowl.

      Below is a spalted citrus bowl 8.5 X 6.75 an 1/8" wall
      and 12 X 8.5 sycamore bowl that still needs sanding in A couple of spots

      These bowls are quite stable in use. They may rock a bit but they still hold salad quite well.
    2. image.jpeg
    3. image.jpeg
    4. image.jpeg
    5. image.jpeg
     
    Last edited: Aug 2, 2016
  17. robo hippy

    robo hippy

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    Turning off a 1/4 inch tenon compared to turning off a 1/4 inch recess, you remove the same amount of wood. Takes me back to the early years of our club when we had a meeting about mounting things on the lathe. My main information source was Richard Raffen, who used a recess. Several of the members of the club, when use of a recess came up, all told about the problems they had when using a recess. Being pretty much a total newbie, I kept quite, and went home to ponder all the problems they had. I had experienced every single one of them. I figured out that I had solved all of those problems, which was why I had and still almost no failures. You experience the same problems with tenons, and you solve them. For me, there is no advantage or disadvantage to either one as long as they are properly made. The one exception I will make is that I will never use a recess on end grain wood. I only split wood for the wood stove.... If I have a questionable piece of crotch wood and bark inclusion near the mount point, then a tenon.

    robo hippy
     
  18. hockenbery

    hockenbery AAW Advisor Staff Member

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    Reed, that is true! However you can use the wood in the tenon as part of the finished piece.
    The wood that was in the recess is on the floor.
    Recesses work fine if you have the wood. Recesses don't work well for small pieces.

    Certainly part of it is comfort level. I can't break a tenon by cranking too hard on the Chuck key
    I can break a recess by cranking too hard on the Chuck key.

    My first Chuck was a precision Chuck that only had recess jaws that expanded as the jaws were pushed down over a cone in the center of the jaws.

    A tenon is so much easier to make when working between centers than a recess so I just naturally went to tenons for about 99% of what I do.
     
  19. Jamie Straw

    Jamie Straw

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    So cool, Gerald. Could you give me a general idea of how the process goes? I might get more out of the wood supply if I know how to do this!
     
  20. robo hippy

    robo hippy

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    Well, the recess can be incorporated into the design as well if you leave the recess in rather than turn it off, which for production work is an extra step and you can't charge extra for doing that. Found out a long time ago that the only ones that really care about the recess are other woodturners. If you can break your recess by turning too hard, you haven't made the shoulder big enough. If I am working between centers, then I only do so till it is time to turn the recess. Never use face plates, just expand into a recess made with a forstner bit. That is production work though and I might consider different techniques for 'Art'.

    robo hippy
     
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