Bending Questions

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Darryl Young
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Joined: Fri Jul 30, 2010 6:44 pm
Location: Arkansas

Bending Questions

Post by Darryl Young »

I have a bender made by John and I bent a sycamore side a month or two back just to get a feel for how to use it. Last night I bent a test side of mahogany for practice before bending my Cuban Mhogany sides. So so far all I've done are test pieces that won't be used on a guitar. I'm close to bending the Cuban Mahogany sides for the 00 I'm building so I want to ask a couple of procedural questions before I get started.

First, the flat edge of the side (that the top will glue against) I believe is usually lined up along the edge of the bending form. I assume it should be aligned along the OUTSIDE edge of the plywood bending form? I ask because the outside 1/4" of the blanket doesn't heat up so it made me wonder if possibly folks lign up on the INSIDE edge of the plywood side of the bending form.

When folks are giving temperatures to go by, it seems it would make at least a little difference where in the stack the thermometer is placed. The stack I've been using is (bottom to top): metal slat, paper, wood, paper, metal slat, bending blanket. I've been placing the thermometer between the blanket and the metal slat. Is that the best place and when most folks give there temperature readings is that the typical location folks are using? In one sense I think it would be better to place the probe against the wood.......but I don't want the probe to indent the side so I haven't done that. And it seems if the wood temps are different than the blanket temps, at least it's a fairly linear relationship so the blanket temp is still meaningful and useful (though may be a little different).

Any tricks for lining up the flat edge of the side, the slats, and blanket (lengthwise and parallel)? I finally lowered the waist caul to help hold things in place while lining things up and that helped prevent some of the shifting.

BTW, the method I used for pre-tapering the sides worked great! I'm surprised how accurate this turned out. Only thing I'll do different on the real sides is add almost 1/8" to the width measurements (to make sure I get the sides cleaned up by the time I've hit the width I want) and I'll be much more careful trimming the profile line on the bandsaw. May even leave a little excess and sand to the line on either my drum sander or 12" disk sander.
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tippie53
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Re: Bending Questions

Post by tippie53 »

I have the vids out on you tube. The think is how hot is the blanket. You don't want to place the thermometer on the wood . Different woods will take different heat but for a rule of thumb 325 to 375 will do the best . Some woods like more water than others.
Here is the link to the bending vids http://www.youtube.com/results?search_q ... 29l0.1l1l0
Let me know if that helps you Darryl
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
Darryl Young
Posts: 1668
Joined: Fri Jul 30, 2010 6:44 pm
Location: Arkansas

Re: Bending Questions

Post by Darryl Young »

Yeah, I watched that video before I bent the test side last night. Still not sure if you line the side up all the way against the outside edge or not (where there is no heat in the heat blanket).

Another question, the very middle of the waist on my sides is right where it should be but a little either side of the waist centerline it isn't bent quite enough. It appears the metal center caul should flex to form the contour of the middle portion of the waist. It doesn't seem the metal is flexing enough and it is mostly making contack right on the centerline.

I pulled the waist caul and the metal is fairly stiff. Also, there is a mahogany block in the center that may be limiting how much the metal can flex (or it may not be a limiting factor, not really sure). I re-installed the waist caul without the mahogany center block and without the blanket and tightened it down against the 00 to see if it would flex/bend to take the shape of the 00 waist. If you really tighten down, the metal will flex and contour with the 00 pattern. Not sure if I can use this much pressure with a blanket without damaging it. I did this 3 times and on the last time left it in this position hoping it would take on the shape of the 00 waist (my thought is this is the tightest wasit I'll likely ever use so if this was the starting point it might be better). So a couple of questions:

1) What is the purpose of the mahogany "filler" block inside the waist caul? Is it to limit the flex of the metal? Since I don't understand it's purpose, it seems it could be limiting the flex of the metal........and it seems the bend would be improved a little if the metal could flex more following the countour of the waist further. So can I bend without this?........or at least cut it narrower where the metal can flex more?

2) Since it requires a fair bit of pressure to flex the metal on the waist caul, could a thiner gauge flex and follow the contour of the waist without applying so much pressure to the blanket? For the record, it's not bad as is......but the contour of the waist on the bend could be improved a little.......so I'm wondering if either of these changes might help that.

Thanks!
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johnnparchem
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Re: Bending Questions

Post by johnnparchem »

I never worried about the waist caul taking the perfect shape of the mold, I just wanted the center on the caul or the high point tp end up in the center of the molds waist. I do the waist first but not all the way. I leave a bit to go. I then do the lower and upper bouts and come back and tighten the waist the rest of the way. This sort of pulls any slop out of the bouts I do not crank it or anything.
tippie53
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Re: Bending Questions

Post by tippie53 »

call me darryl
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
Darryl Young
Posts: 1668
Joined: Fri Jul 30, 2010 6:44 pm
Location: Arkansas

Re: Bending Questions

Post by Darryl Young »

Ok, I'll give you a call later. Again, I don't know if this would help or not so I'm just speculating (and it's very close as is). Was hoping it might pull the waist tighter where it transistions to the lower bout.

I profiled and trimmed the Cuban Mahogany sides and just finished bending the scrap from one of the sides. It seemed to bend well following the same method I used for the test side. When it cools I'll remove it and then know more.
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