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Bending Form Layout
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10101&t=16826		 Page 1 of 1
Author:  John Killin [ Fri Apr 11, 2008 12:17 pm ]
Post subject:  Bending Form Layout
I'm getting ready to cut the wood for my exterior mold. I'm working on a 000 using the Stew-Mac plan. I’m not sure, but I am thinking that if I’m careful, I could use the center section of off cuts from the exterior mold to make a bending form.

I plan on bending with a blanket in a fox style bender. My question is, when you are laying out a bending form, do you cut down the center line of the guitar for the bottom, or do you add a couple of inches to the center line? So is it a true half outline (minus blanket and side thickness), or is it the half outline with additional material on the other side of the center line.

I hope that makes sense.

Thanks,

John
Author:  Mattia Valente [ Fri Apr 11, 2008 12:28 pm ]
Post subject:  Re: Bending Form Layout
killin5 wrote:
I'm getting ready to cut the wood for my exterior mold. I'm working on a 000 using the Stew-Mac plan. I’m not sure, but I am thinking that if I’m careful, I could use the center section of off cuts from the exterior mold to make a bending form.

I plan on bending with a blanket in a fox style bender. My question is, when you are laying out a bending form, do you cut down the center line of the guitar for the bottom, or do you add a couple of inches to the center line? So is it a true half outline (minus blanket and side thickness), or is it the half outline with additional material on the other side of the center line.

I hope that makes sense.

Thanks,

John


Mine have additional material past the centerline, following the shape of the other half. That's because all of my shapes have rounded heels and butts, not Martin-esque flattened areas at the butt and heel.
Author:  Michael Dale Payne [ Fri Apr 11, 2008 1:03 pm ]
Post subject:  Re: Bending Form Layout
The mold should be the inside dimension of half the body less the blanket and slat thickness if below the wood. I use 1" past center line continuing the arc to allow a tad of over bend but this is not at all critical since you trim to center after the bend anyway.

To me the most important thing is getting the body shape right. This is often missed because new builders will cut the body shape to the outside dimensions of the guitar, but should be inside dimensions less the thickness of anything between the wood and the mold. If you use your blanket on the inside that would be less the blanket thickness and less one slat thickness if you put the blanket on the outside of your wood it would be less one slat thickness. Anyway you arrange your sandwich you want the finished bend on the inside of the wood to match the inside dimension of the guitar. Some builder even build a tad less than this for the body shape to account for spring back.
Author:  Frei [ Sat Apr 12, 2008 2:06 pm ]
Post subject:  Re: Bending Form Layout
You might want to take some off the ends also, for springback. I got about 3/4 inch on the back at least, and about 1/2 on front, mabe a bit less. This is my new dred mold.Just take the pattern and set it at the peak of the curves and draw the line to the amount of cutoff. This may vary depending on your experience. I got lots of springback, and I heated it plenty of times etc... Mahogany and Paduk had same amount of spring. I will then use the bent side wood, as close as I can get it, to make the outer mold, as my wood doesnt form to the mold that well when I would put it in.


Image
Author:  Shane Neifer [ Sat Apr 12, 2008 9:53 pm ]
Post subject:  Re: Bending Form Layout
But also remember that you can add that extra onto the bottom with some scrape wood. You will to be VERY accurate on your bandsaw when you cut it out though. Me, with LOTS of woodworking experience, I just used some other wood (MDF actually).

Shane
Author:  John Killin [ Sun Apr 13, 2008 8:08 pm ]
Post subject:  Re: Bending Form Layout
Thanks for the tips. I used Todd's approach while cutting my outside mold pieces and now have the center part that I can use for the bending mold. I wasn't sure if I would be able to cut both with out messing up at least one of the parts. I used a scroll saw and pulled it off. In high school I was banned from using the scroll saw by my shop teacher. I had too many broken blades. There is a mental thing with me and the scroll saw.

So for the bending mold, this being my first guitar bend, should I make my mold to the shape of the guitar minus the side and blanket thickness, or should I exaggerate the bends? I don’t have a technique yet, so I’m not sure if overcompensating thing might be a bad thing.
Author:  Guest [ Tue Apr 29, 2008 3:15 pm ]
Post subject:  Re: Bending Form Layout
I have finally completed my exterior mold. It came out pretty good. I'm ready to move on to the solid form. bliss

Todd,

You cut a groove in the waist on your solid form. Is there a part on the waist press on your bender that registers there? I hadn't planned on doing anything like that on my bender. The bender will be my next project.

And without starting a new thread, is MDF suitable to build a fox bender with?

Thanks,

John
Author:  John Killin [ Tue Apr 29, 2008 3:17 pm ]
Post subject:  Re: Bending Form Layout
That was me in the last post. I could have sworn I was logged in when I started the reply.

John
Author:  Brock Poling [ Tue Apr 29, 2008 4:03 pm ]
Post subject:  Re: Bending Form Layout
MichaelP wrote:
The mold should be the inside dimension of half the body less the blanket and slat thickness if below the wood. I use 1" past center line continuing the arc to allow a tad of over bend but this is not at all critical since you trim to center after the bend anyway.

To me the most important thing is getting the body shape right. This is often missed because new builders will cut the body shape to the outside dimensions of the guitar, but should be inside dimensions less the thickness of anything between the wood and the mold. If you use your blanket on the inside that would be less the blanket thickness and less one slat thickness if you put the blanket on the outside of your wood it would be less one slat thickness. Anyway you arrange your sandwich you want the finished bend on the inside of the wood to match the inside dimension of the guitar. Some builder even build a tad less than this for the body shape to account for spring back.


Along these lines.... I put the blanket on top, but I still make the interior support .100 smaller for the side and the bottom slat.
Author:  Frei [ Tue Apr 29, 2008 6:55 pm ]
Post subject:  Re: Bending Form Layout
Oh, man, theyre gettin plywood from China too?? pfft
Author:  John Killin [ Wed Apr 30, 2008 3:58 pm ]
Post subject:  Re: Bending Form Layout
Can you point me to a photo of the waist caul and the tension bar. I have an idea of how this would work, but I think I am missing something.

I asked about the MDF because I have some laying around that I'm trying to come up with a use for. I bought it for my exterior mold and then rethought it and used plywood. Unfortunately I ripped it into strips so I can't use it for a radius dish. I was thinking of using it for the bender itself. Not the solid form.

Thanks,
John
Author:  John Killin [ Thu Jul 03, 2008 9:27 pm ]
Post subject:  Re: Bending Form Layout
Ok being a new guy and asking some basic questions I figured I would post some pictures of what I am now calling a success. So here is the fruit of this thread.
Attachment:
Bender 2.jpg
Author:  John Killin [ Thu Jul 03, 2008 9:31 pm ]
Post subject:  Re: Bending Form Layout
And the Mold.
Author:  John Killin [ Thu Jul 03, 2008 9:39 pm ]
Post subject:  Re: Bending Form Layout
Pattern routing was a big success. My only real issue with it once I figured out what I was doing was I had some tear out in the plywood. The router grabbed the piece and flung it a couple of times. It only took a couple before I stopped. This was on the smaller pieces for the caul.
Attachment:
Bender Chip.jpg


I still need to make the spreaders for the mold. I'm sure I'm doing something wrong here. Any tips on doing these smaller pieces would be appreciated.

Thanks for getting me this far.

John
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