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Thread: Dry Bending Sides

  1. #1
    Registered User David Houchens's Avatar
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    Default Dry Bending Sides

    I've heard someone mention dry bending mandolin sides. Have any of you dry bent guitar sides? Thanks

  2. #2
    Adrian Minarovic
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    Default Re: Dry Bending Sides

    Quote Originally Posted by David Houchens View Post
    I've heard someone mention dry bending mandolin sides. Have any of you dry bent guitar sides? Thanks
    I don't see any principal difference in mandolin or guitar side bending. Guitar sides being often thinner than mandolins' it should be even simpler. I never bent guitar sides but I bent wood for many other things.
    All you need to know to succesfully bend sides is that heat and water soften the bonds within wood (lignin?) and allow for the plastic compression of fibers. You need to remember that heat or water do work alone but not as effectively as combined so you need to go slowly and be prepared that there can be greater residual stress in the wood than with water/heat combo.
    When bending curly maple water is often reduced or even bent dry as the water turns to steam and enters the endgrain of the curl faster than the side-grain between the curls and causes uneven softening and kinks in bent sides. water also reduces tensile strength of the piece at the endgrain so thay are easier to break - you need good backing strap (with grips at the ends) and lots of force against iron to bend them smoothly.
    If you soak curly maple thoroughly you need to proceed slowly and with good strong backing against form/ iron and preferably securing the outside against tension stresses (anchored ends of wood to backing strap, some use coarse sandpaper attached to strap tah will "grip" the wood)
    Adrian

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  4. #3
    Registered User David Houchens's Avatar
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    Default Re: Dry Bending Sides

    Thanks Adrian. I've bent many sides using heat and water, just never without water. I was thinking slower with a little less heat to prevent scorching.
    Having just experienced some side to side rippling in a guitar set , I thought maybe heat without the moisture may help keep this from happening.

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    Registered User sunburst's Avatar
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    Default Re: Dry Bending Sides

    David, I've bent sides without added water. There is always some moisture content in wood (unless it is freshly oven died), and it seems to me that some wood bends better with less water and some bends better with more water. Some mahogany needs to soak for a short time, some curly maple is best with no added water or just a light spritz. YMMV

    I believe Adrians evaluation of how wood bends is slightly off. As I understand it, heat and moisture soften lignin and allow wood cells to slip past one another rather than compress. That explains why we must 'compress' the inside of the bend and cannot 'stretch' the outside of the bend. When wood fibers slip past one another on the outside of the bend it results in failure.

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  7. #5
    Adrian Minarovic
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    Default Re: Dry Bending Sides

    Quote Originally Posted by sunburst View Post
    I believe Adrians evaluation of how wood bends is slightly off. As I understand it, heat and moisture soften lignin and allow wood cells to slip past one another rather than compress. That explains why we must 'compress' the inside of the bend and cannot 'stretch' the outside of the bend. When wood fibers slip past one another on the outside of the bend it results in failure.
    Perhaps I didn't use good vocabulary, but the cells are long tubes that are pretty much connected into one continuous pipeline all the way up to the top of tree. They cannot just slip one past another. The cellulose fibers that are the building material of the cell walls are also held together by lignin and that allows them to slip within the wall, but that results necessarily into some compression of the wall as whole. At least that is how I understand wood structure being compressed during bending. But I had the books about this in hands more than 20 years ago and memory can be unreliable...
    Adrian

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    Registered User David Houchens's Avatar
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    Default Re: Dry Bending Sides

    Thanks to you both. I'll have to experiment with dry
    heat and go slowly.

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    Henry Lawton hank's Avatar
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    Default Re: Dry Bending Sides

    David Iíve been putting together a low priced DIY steam tube and shaping dryer form. I used a 4Ē tube size but it could be built larger for your guitar work. I found the heater on EBay and the steamer at Amazon both moderately priced. Iím still working on the form. Most are used and built horizontally but Iím gonna kick it up on itís side for an easier centered wrap from the top. This way I can lock down the scroll end then work it back as it lays on around to the bottom point area. The heater is wider than my ribs making it more cumbersome to use horizontally.
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    "A sudden clash of thunder, the mind doors burst open, and lo, there sits old man Buddha-nature in all his homeliness."
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    Henry Lawton hank's Avatar
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    Default Re: Dry Bending Sides

    I looked back at my records and found both the steam generator and the heat strap and both came from Amazon. The Earlex was just under $70 and the strap about $73. The long sweat tray is a couple short trays from Wally World like the one under the Earlex steam generator bonded together. Not much else to buy but the stainless straps and hold down clamps. A few knitting rings hold the tube to the long center support to prevent the tube bowing under the higher temperature when in use. The black top exhaust tube has a discarded deodorant roller ball that blocks it till the pressure builds enough to pick up its weight. The top tube inserted into the lower segment keeps the ball contained while slots let the steam past the ball block on out the tube. Again I could use some help with my photos orientation.
    "A sudden clash of thunder, the mind doors burst open, and lo, there sits old man Buddha-nature in all his homeliness."
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    Registered User amowry's Avatar
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    Default Re: Dry Bending Sides

    On the issue of the cells slipping vs. compressing: With figured maple, which we mandolin builders use most often, the "curl" enters and exits the faces of the wood repeatedly, so it effect each cell is very short. So, with figured wood, I'd say that cells do indeed slip past each other to facilitate the bend. I believe that's why there's less springback with figured wood, and also why if you get figured wood too wet it will fracture easily-- the lignin softens, allowing the short fibers to separate from each other. When that happens at the face of the wood, it equals a fracture .

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    Registered User David Houchens's Avatar
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    Default Re: Dry Bending Sides

    Hank, are you steaming the wood? I've bent hundreds of sides using moisture and heat. My questions were about bending the sides dry. Just playing with the idea. Going to try one soon I guess.

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    Henry Lawton hank's Avatar
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    Default Re: Dry Bending Sides

    I read moisture and heat meant a bending iron and spray bottle might be causing your rippling wood deformation. Perhaps a steam bath and drying mold might cause less stress to the wood with less deformation and fracturing. I’m still making this up as I go along but hoped it might be a low cost option for your rippling deformation with your current methods. I’m looking forward to your dry bending information to come.
    "A sudden clash of thunder, the mind doors burst open, and lo, there sits old man Buddha-nature in all his homeliness."
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  20. #12
    Adrian Minarovic
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    Default Re: Dry Bending Sides

    Quote Originally Posted by hank View Post
    I read moisture and heat meant a bending iron and spray bottle might be causing your rippling wood deformation. Perhaps a steam bath and drying mold might cause less stress to the wood with less deformation and fracturing. I’m still making this up as I go along but hoped it might be a low cost option for your rippling deformation with your current methods. I’m looking forward to your dry bending information to come.
    OFten some rippling is inevitable unless you have precise mould and counter piece that will "iron" the piece flat and keep it there till the bend is fixed. Tight bending strap helps, but the stresses within wood especially with varying grain orientation within piece will have to show somewhere.
    Adrian

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  22. #13
    Henry Lawton hank's Avatar
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    Default Re: Dry Bending Sides

    Adrian that’s part of why I’m going with a vertical wrap to make it easier get a tight centered fit on the rib form. I also divided the width of a guitar stainless bending strap and preshaped it to fit tight like a glove around the scroll and inside hip. I’m using my inside mold assembly blocks starting at the scroll and working the rib and straps tightly into place till finally ending at the heater strap temp probe that also must have a tight fit for accurate temperature control. I’m guessing 10 to 15 min. in the steam tube and another 2 to 5 min. to get it on the form tight. Lastly low heat for another 30 min. with fingers crossed and perhaps a good IPA.
    "A sudden clash of thunder, the mind doors burst open, and lo, there sits old man Buddha-nature in all his homeliness."
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    Registered User amowry's Avatar
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    Default Re: Dry Bending Sides

    I'd venture that one why reason why most luthiers don't use steam is that it gets the wood wetter then necessary, which makes figured wood more prone to breaking, and makes rippling more likely. In my experience less water is best (just a quick spritz right before bending, with figured woods). I bend a lot of bindings, lining, etc. totally dry. A benefit of using some water, though, is that it helps keep the wood from scorching.

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    Henry Lawton hank's Avatar
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    Default Re: Dry Bending Sides

    Thanks for the heads up on my folly MR. Mowry. It is well taken and noted. I am a hobbyist having fun here hoping to give back and share low cost alternatives but had no idea my methods don’t work well and minimal water dry bending is the preferred method. Sorry for my intrusion in this thread. Everyone back on your head!
    "A sudden clash of thunder, the mind doors burst open, and lo, there sits old man Buddha-nature in all his homeliness."
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    Registered User David Houchens's Avatar
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    Default Re: Dry Bending Sides

    Hank, No intrusion felt here. I appreciate all suggestions on all subjects. Feel free to comment any time.

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    Adrian Minarovic
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    Default Re: Dry Bending Sides

    I think (just musing here) that there is probably vast difference between using tiny or medium amount of water and using fully steamed wood, especially figured.
    If you use no or very little water it won't get through the piece to soften the outside in the runout areas to split easier. It just wets the inside and helps in compression. But once you add more water and it soaks through the endgrain to the other side it will make the outside softer in the runout areas then between them and prone to separating under tension. But if you fully steam the wood (like in furniture factories under pressure and temp slightly above boiling point) the whole mass becomes much more pliable and even though the outside is softened and can break in the runout areas since the inside is also much more softened than just by little water and heat, the whole can bend without fractures. If you use good compresion belt and proceed slowly and steadily around form you are pretty safe, IMO. Some woods really behave almost like wet noodle when properly steamed. I bent some ash sticks (3/8" thick almost 1" wide) for snow shoes many years ago and it went much easier than I thought after I cooked them in water thoroughly (the first attempts with dry heat failed). And that was straight grained wood without defects.
    Adrian

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    Registered User sunburst's Avatar
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    Default Re: Dry Bending Sides

    From my own experience, not from anything I've read or been told, here is a 'hypothesis' that I have formed.
    First a little background;
    We know (as mentioned in this thread among others) that to successfully bend wood we need to compress the inside of the bend rather than stretch the outside of the bend. We know that over-stretching of the outside of the bend results in failure. In other words, the piece of wood breaks.
    We know that in normal wood the neutral axis of a symmetrically shaped piece of wood is at the center of the piece at normal temperatures, but at elevated temperatures the neutral axis moves toward the outside of the bend. That is, in large part, how we can get away with bending thin pieces without using a bending strap that eliminates stretching of the outside of the bend (as used in steam bending).
    I know from my own experience that sometimes a piece of wood will bend on the bending iron to an extent and refuse to bend any more. If I try to continue the bend the piece is likely to break. If instead I lay it aside and let it cool, I can then continue the bend.
    So here's my hypothesis:
    As we apply the piece of wood to the bending iron we heat the side contacting the iron. Early in the process the wood is much hotter at the inside of the bend than it is at the outside of the bend. That assists us in bending because the cooler outside of the piece resists stretching and subsequent failure better than hotter wood. As we continue to bend the piece the heat goes through the piece so that the outside of the bend is nearly as hot as the inside of the bend. That is when failure is likely. Let it cool and the process begins again when we go back to the bending iron; we once again get a temperature gradient through the wood and we can continue a bend that was 'stalled out' and in danger of failure.

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  33. #19
    Adrian Minarovic
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    Default Re: Dry Bending Sides

    Quote Originally Posted by sunburst View Post
    From my own experience, not from anything I've read or been told, here is a 'hypothesis' that I have formed.
    First a little background;
    We know (as mentioned in this thread among others) that to successfully bend wood we need to compress the inside of the bend rather than stretch the outside of the bend. We know that over-stretching of the outside of the bend results in failure. In other words, the piece of wood breaks.
    We know that in normal wood the neutral axis of a symmetrically shaped piece of wood is at the center of the piece at normal temperatures, but at elevated temperatures the neutral axis moves toward the outside of the bend. That is, in large part, how we can get away with bending thin pieces without using a bending strap that eliminates stretching of the outside of the bend (as used in steam bending).
    I know from my own experience that sometimes a piece of wood will bend on the bending iron to an extent and refuse to bend any more. If I try to continue the bend the piece is likely to break. If instead I lay it aside and let it cool, I can then continue the bend.
    So here's my hypothesis:
    As we apply the piece of wood to the bending iron we heat the side contacting the iron. Early in the process the wood is much hotter at the inside of the bend than it is at the outside of the bend. That assists us in bending because the cooler outside of the piece resists stretching and subsequent failure better than hotter wood. As we continue to bend the piece the heat goes through the piece so that the outside of the bend is nearly as hot as the inside of the bend. That is when failure is likely. Let it cool and the process begins again when we go back to the bending iron; we once again get a temperature gradient through the wood and we can continue a bend that was 'stalled out' and in danger of failure.
    That sounds correct to me (for bending dry or with just little moisture on the inside surface) and that's what I've been doing for curly maple sides. It's simplest way for free-hand bending over iron.
    I've done full steaming just with straight grained wood but I see that Siminoff used it for quite thick (1/10"-1/8") sides on his bending jig with smooth bends and I guess Collings or Ellis are doing it that way with their bending machines like Gibson does.
    Adrian

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    Registered User amowry's Avatar
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    Default Re: Dry Bending Sides

    Yep, I agree too, and if I'm bending on a hot pipe I only apply water to the inside surface, like Adrian mentioned. I think that helps aid compression while preventing too much stretching on the outer surface.

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