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Thread: side bending - cracking

  1. #1
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    Default side bending - cracking

    I'm practicing bending sides with a bending iron and some poplar.

    I planed the sides down in a planer to @ .25" thick.

    I took off a smidge with my safety planer in the drill press.

    I'm freehanding it.

    Should I get one of those metal backing strips to help? I Seem to get to about 80% of my bend and then it cracks...

    Thanks in advance, ad

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    Default Re: side bending - cracking

    The sides with my Siminoff kit are only 1/8" thick. Plane them down to this and see what happens.
    Ralph
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    Default Re: side bending - cracking

    You might want to do some research on whether poplar can be bent or not- some woods just don't bend well; I haven't heard yea or nay on poplar.

    I'm building my first mandolin, and I can tell you that figured maple is a bear to bend without breaking, especially in the tight curves. I wound up taking my sides down to 0.10" (which is plenty, and is recommended by some makers) and using a metal backer. Even then the tight bends were dicey. the backer strip really helps. Don't get them very wet at all- it makes them more likely to break in the curl, which is really end grain.

    Rick
    Last edited by Rick Lindstrom; Dec-31-2008 at 7:05pm. Reason: typo

  4. #4

    Default Re: side bending - cracking

    I agree, 1/4" is too thick. The dulcimer I built has 1/8" sides and it was iffy to bend in mahogany. I don't have a steam box so I soak the pieces overnight and bend them over a hot pipe, propane fired 3" black iron job.

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    Default Re: side bending - cracking

    Holy Toledo, you guys! Even 1/8" (.125" or about 3mm) is pretty thick, but at .250" you'll have to steam bend it like boat parts, probably using a backing strap. I bend guitar sides at about .080", and uke and pancake mandolin sides a bit thinner, around .070".

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    Default Re: side bending - cracking

    Quote Originally Posted by Bob Aliano View Post
    I agree, 1/4" is too thick. The dulcimer I built has 1/8" sides and it was iffy to bend in mahogany. I don't have a steam box so I soak the pieces overnight and bend them over a hot pipe, propane fired 3" black iron job.
    I reiterate (sadder but wiser)- when you get ready to bend figured maple, the wetter it is, the more likely to break.

    Rick

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    Default Re: side bending - cracking

    Doh its birch, not poplar....

    Thanks,ad

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    iii mandolin Geoff B's Avatar
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    Default Re: side bending - cracking

    .07-.08" is what I usually do, especially in the tight curves

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    Default Re: side bending - cracking

    whats the best way to get from .25 to .08?

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    Default Re: side bending - cracking

    A thickness sander is one of the best ways, a belt sander and a board to stroke the side against the belt, a drum sander in a drill press with a fence, and other ways that aren't so easy like planing or scraping by hand.

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    Default Re: side bending - cracking

    I did mine on a cheap oscillating sander I got at Harbor Freight. Make a fence and away you go.

    Good for various other stuff too.

    A Safe-T-Planer on a drill press would do it as well, and also be good for other stuff like contouring your plates.

    Rick

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    Default Re: side bending - cracking

    .70-.80 works for me. Never bent birch but I'd think anything 1/4 would be tough to do. May be able to rip it on the bandsaw, just the blade width will get ya closer. Safety planner will work also. Thickness sander would definitly be the best. Go slow.

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    Registered User Bill Snyder's Avatar
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    Default Re: side bending - cracking

    For sides I would get close with my table saw and finish up with a plane. If you have access to a thickness sander that would be the way to go or the sanding drum on a drill press with afence set up.

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    Default Re: side bending - cracking

    I use my table saw to get close then hand plane and scraper to the final dimension. Also use a spoke shave and shavehorse for shaping necks.

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    Default Re: side bending - cracking

    Backing strap? YES absolutely. Thickness? .25 is about twice as thick as it needs to be and then some.

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    Default Re: side bending - cracking

    Thanks for the advice. I will try it with a thinner piece today.

  18. #17
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    Default Re: side bending - cracking

    Yeah, 1/4" is way too thick, unless you're laminating rims for one-legged drums. Also, make sure your iron is hot enough. Water should pop and sizzle as you lay the wet side against the iron. Then, don't try to make the bend on a small contact between the wood and the iron. Rock back and forth - around the arc of the iron - heating, at least, a couple inch area, all the time.

    I've not found a metal backing strip to be of any help, at all, other than to introduce something else to maintain control over. I merely wipe the wood - side that's going against the iron - with a wet rag, re-wetting, as necessary. Some wood bends easier with no wetting at all. Main thing is, go slowly, and feeeeeel what's happening. It's like learning to ride a bicycle. You fall down a few times, but after a bit, you say "Oh, so that's how it works."

    Of course, after you think you've got it all figured out, there comes that piece of wood that keeps you humble, and you say "Jeeze!, have I ever done this before?" Welcome to the many faces of mandolin building.

    Happy New Year

    Gene

  19. #18
    Violins and Mandolins Stephanie Reiser's Avatar
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    Default Re: side bending - cracking

    Adam,
    I usually sand my sides down to no less than .065", and actually try for that thickness. A little heavier for the long section bass-side. A backing strap for sure. Stew-Mac sells them, and they aren't too expensive. Well worth it. What are you using for a bending pipe? I use four different sizes of 6" iron "nipples", which are plumbing fixtures that you can pickup at Home Depot or any well supplied plumbing parts center. I have 1-1/4" to 2". They work well, using a propane torch, but I may breakdown and get an electric one. I sand my sides down to thickness using a 4" x 36" belt sander, which was $99 at HD, but I am planning to upgrade to a 6" x 48" in the near future. I think someone mentioned a spindle sander with a fence, and that is also a great idea. The violin boys just plane them down to thickness with a hand plane. For what it is worth, the part I hate to bend the most is the S-shaped section that goes around the nose, or dovetail, area to the first point. This would be on an F-model. IF you're building an A you would not have this issue. Siminoff suggests stopping at the centerline, but I depart from his literature by carrying this side piece on into the scroll. I do not soak the wood, just spritzing it. IF you are experiencing scorching of the wood, try soaking a cloth or heavy-duty paper towel in water and placing this between the wood and the pipe. Mario P. has suggested to me here to put something in the end of my pipe to help spread the flame more so as not to experience "hot-spots" which cause scorching, which I have upgraded to since these pics were taken. Take your time, and with some practice you should be able to feel the wood let go and assume its new shape. On guitars, I actually prefer hand-bending as opposed to mechanical benders, and the whole bending process is very enjoyable and is one of my favorite segments of the instrument building process.
    Good luck! and show us how it went.
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    Last edited by Stephanie Reiser; Jan-01-2009 at 8:42am. Reason: mis-spelled word
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    I may be old but I'm ugly billhay4's Avatar
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    Default Re: side bending - cracking

    .07 or .08" thick. Easy on the water. Spritz them is all. Slow with the heat and wait until the wood wants to bend itself.
    Bill

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    Default Re: side bending - cracking

    It's really the heat that is doing the job in allowing wood fibers to slip and then rebond to one another in the new shape. The water or steam is just carrying the heat into the wood and preventing scorching. One trick that some of the guitar builders are using is to put a little bit of Downy fabric softener in the water. Another is to use a commercial veneer softener available over at "Joe Woodworker". It's a site devoted to veneering and vacuum jigs. Very interesting stuff.

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    Default Re: side bending - cracking

    Here's a link to the Super Soft II stuff.

    http://www.joewoodworker.com/veneering/flattening.htm

    Apparently, the effect only lasts for 4 to 7 days, and then the wood stiffens back up. This could be fantastic for doing F style mandolins.

  23. #22
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    Default Re: side bending - cracking

    maybe i'm going too fast, or maybe my iron isnt hot enough... what temp should I be bending at?

  24. #23
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    Default Re: side bending - cracking

    The iron should be hot enough to make water sizzle, but not hot enough that is immediately scorches the wood.

    If you're working sides that have been wetted, you should hear the water popping and sizzling a bit when you bend them. Sometimes you'll see steam coming through the wood (depending on species).

    My experience has been that mahogany will bend nicely when soaked in hot water for an hour or so, but figured maple will break instantly if it's more than just a bit wet.

    In the course of bending the sides for the mandolin I'm making, I turned no less than five sides into piles of two inch shards before I finally managed to get a set bent (and this was for an A style!). When I ordered the wood from Old Standard, I told them that it was to be my first mandolin, and they were nice and sent extra wood so that I was left with enough even after breaking up a bunch. They probably knew what was going to happen.

    YMMV

    Rick

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  26. #24
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    Default Re: side bending - cracking

    Stephanie, after reading your reply, I also use the pipe/propane to bend. I usually take a wet rag, ring it out a bit and rub onto the wood before bending. Accidently dropped the wet rag on the hot pipe, ding, ding, why didn't I think of that! Lots of steam and no more scorched wood. Thanks for mentioning it. Jerry

  27. #25

    Default Re: side bending - cracking

    I'm trying to bend maple sides and have managed to crack three pieces. Thickness is about .075. I've tried soaking, dry, and moistened. Soaking definitely makes the cracking problem worse, at least with this material. Here's a photo of the crack after about 40 minutes of what I would consider very gradual bending on a stewmac bending pipe:
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    This wood is from a 2007 LMI kit and it's been sitting in the hot SW desert since then. Can the wood be too dried out?

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