Determine where and much much to bend for ribs?


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Dear all:

Hi I was wondering if anyone has good precise ways of measuring and marking where and how much to bend when bending ribs (especially upper and lower)? As ribs are flat pieces I ha be been wondering how experienced luthiers determine how much and where to bend to form the same radius and curves of the mold. Thanks.

 

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11 hours ago, liang7079 said:

Dear all:

Hi I was wondering if anyone has good precise ways of measuring and marking where and how much to bend when bending ribs (especially upper and lower)? As ribs are flat pieces I ha be been wondering how experienced luthiers determine how much and where to bend to form the same radius and curves of the mold. Thanks.

 

Practice, practice, practice...

 

...,until you don't need to think about when and where and how much any more.

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For the c-bout I mark the center of the corner blocks with a pencil. Then measure the distance with a flexible measuring tape between the two marks keeping the tape flush against the mold. Then I mark the rib stock and pre-cut to the length I need. You can do the same for the lower bout, although I don’t. The picture shows (if you click on it to zoom in) where I mark the rib and blocks. Mostly I do it to help make the second corner block bend in the right place. 
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I am self taught, so maybe my advice is no good.  But...

I place a pencil Mark at one end of the rib to show where it will fit in the block. Then i bend trying to get close to the final shape.  Be careful to keep the bends at right angles to the rib so you don't wind up with a DNA spiral shape that doesn't sit flat.

The working from the pencil Mark I use a little heat to carefully adjust the curvature to exactly fit the mold, working on just a few cm at a time.  Be very careful not to overwork the piece.  The pencil Mark gives you a reference point for placing the rib in the mold to check shape.

I absolutely agree about going close to 1mm thickness, no more than 1.2mm.  And agree that soaking the wood leads to flame splits.  Let the wood dry out if the wood starts bending at the flames (stop immediately!) rather than bending in smooth continuous curve.

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Thanks for all the replies, I agree more practice with cheap ribs and Jim I will try again with the way you marked the ribs, I did the measuring with a cotton string which I think was probably too soft and wasn't stable enough to keep the length / shape to help marking the spots.

Merry Christmas everyone :)

 

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22 hours ago, J.DiLisio said:

If you're interested in technique, Burgess posted a video a few months back showing how he bends ribs with his body weight pulling the strap against the iron. 
It actually works really well and allows you to use thicker stock if you want to. 

Hi any direct link to the video? Cheers.

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