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| Bending Molds: Springback Compensation? http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=917 |
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| Author: | Mattia Valente [ Tue Feb 01, 2005 7:41 am ] |
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Right, so I've built and used a mold for my first two bodies, and it worked well enough, but not quite to the point where I'm not going to be re-building it :-) The thing's this: The last time around I took the basic shape (outline by the mold), made it smaller by the amount of the sandwich+side thickness, so the result would fit into the mold perfectly. I also made the waist a little deeper, and brought the ends in a little (and in the process slightly messed up the clean curves on lower and upper bout that I was aiming for and had effectively transferred to the mold..hence the re-build). My question to you guys is this: how much compensation, if any, do you add to your bending mold? How far 'in' do you bring the lower and upper bouts? How much additional bend do you give the waist? How do you 'fair' these curves in so as not to 'mess' with them overmuch? I've already got the parts for the 2 outside molds I need to make (Medium Jumbo and a Parlour, although possibly more of an 00) rough-cut, and I'll be moving on to the bending molds when those are finalized and assembled. Just a little fine-tuning left on the Jumbo (slightly too flat spots) and a bit more on the Parlour before I whip out the pattern bits and make MDF dust! |
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| Author: | LanceK [ Tue Feb 01, 2005 7:59 am ] |
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None- for me its a non factor. I dont worry about overbending. I just pull the ends in and blockem up. |
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| Author: | Michael Dale Payne [ Tue Feb 01, 2005 8:00 am ] |
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Mattia as simple as it sounds I bend cook for 10-15 min. allow to cool for 24 hrs. then cook for 10 min. again and allow to cool. I find this seems to relieve most of the spring back left in the side after the first cook. Nothing scientific about it, but kid of like stress relieving steel. When you hot form steel you impart stress inherent to the form shape. You eliminate the stress by heat treating. |
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| Author: | Mattia Valente [ Tue Feb 01, 2005 8:12 am ] |
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So that's two votes for no compensation at all other than size for the side 'sandwich' if I'm reading this right.. |
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| Author: | Kelby [ Tue Feb 01, 2005 8:18 am ] |
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Hey Mattia, I'm anxious to hear people's response to this question. Personally, I don't use any compensation at all. Although the sides do springback a little after bending, it's nothing a good body mold and some spreaders won't cure while I glue everything up. Cheers, Kelby. |
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| Author: | Dickey [ Tue Feb 01, 2005 8:21 am ] |
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I compensated my last constructed mold about 3/4 Inch on the tail, about 3/8 " at the neck, and nothing at the waist. Lance is right, most folk don't worry about it. It just made sense to me to compensate a little, thus making glueup a little less stressed. Someone hand bending would keep on bending until it hit on the money. But like Lance, aw shucks, it just doesn't matter all that much. I do like it compensated, but I don't plan to retrocurve the others I have, just when building new ones I'll do a little of that. |
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| Author: | Michael Dale Payne [ Tue Feb 01, 2005 8:21 am ] |
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Yep as far as I am concerned |
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| Author: | Colin S [ Tue Feb 01, 2005 9:17 pm ] |
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No compensation at all. Just the same as the mould with allowance for side thickness etc. Why over complicate things. Springback isn't a problem, that's what the mould is for. I also reheat the next morning, after trimming to length and sanding then I put it in the mould still warm. Colin |
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| Author: | Mattia Valente [ Tue Feb 01, 2005 10:37 pm ] |
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OK, it's looking like a landslide victory for 'no springback compensation'. I'll see if the cutout pieces from the mold making are big enough, otherwise I might include a minimal amount of compensation at the end, so as not to be wasteful ;-) Dissenting voices let yourselves be heard now! |
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| Author: | Dickey [ Wed Feb 02, 2005 12:44 am ] |
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I started adding compensation to my molds based on Collings doing the same. I just wanted to try it, and it works well. |
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| Author: | rlabbe [ Wed Feb 02, 2005 2:57 am ] |
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I like compensation. Like the others, I won't go back and compensate the molds that are uncompensated, but if you can get a more exact bend with no added effort, why turn your nose up at it? It's easier than the bake/cool/bake method. Just bend, then slap it in the outside mode. Done. |
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| Author: | Mattia Valente [ Wed Feb 02, 2005 3:18 am ] |
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What parts do you compensate? Just the ends? I'm thinking I might add a little at the ends, since I can compensate there without having to worry about 'messing' with the curves overmuch, but leave the waist alone. |
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| Author: | Colin S [ Wed Feb 02, 2005 3:46 am ] |
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Mattia, Don't overcomplicate it. It's really not neccessary. Just go smaller than your mould by the thickness of the side and slat. That's all that's needed. Colin |
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| Author: | jfrench [ Wed Feb 02, 2005 3:51 am ] |
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No compensation here either, and usually my sides hold their shape perfectly in a half mold with nothing clamping them to it. Regards, Joshua French |
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| Author: | rlabbe [ Wed Feb 02, 2005 4:38 am ] |
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Mattia, just a bit at the ends (1/4" max?) and a bit at the waist. Like everyone says, it is not necessary, it's more of a nicety. |
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