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My mold is made to the dimensions I want the instrument to be.
My mahogany sides are sanded down to 080".

My sides spring back when the clamps come off some. I am not sure what's acceptable. I made a body mold, so I know that once the top and bottom are glued on that will solve some of the problems, but I am guessing that's not the way it should be done. If done correctly do the sides hold there shape?

I am wondering if I am not getting the sides hot enough or if I am not leaving them up to temperature long enough.

I have an infrared temperature gun that indicates it is getting up to nearly 300º. Once it gets up to that temperature, I turn down the heat.

I leave it clamped for 24 hours.

The sandwich:
I start with some Home Depot aluminum flashing, then very wet brown paper, the dampened side, more wet paper the heating blanket, and topped off with more aluminum flashing.

I am not using tinfoil. I have heard it's used to protect the wood if you are using Spring Steel, which I am not using.

Any suggestions would be much appreciated.

Thank you

Well, a certain amount of springback is ok. As long as you can get it to conform to the sides of the mold with your spreaders, adding the top and back will fix it in place nicely.

Obviously the less springback the better, but there's usually some, and it will vary from piece to piece.

There's a bending tutorial by Blues Creek which is essentially what I do, but then I leave the heat on between 280-310 for 15 minutes after it's bent to cook off excess water.

I would also say that I don't make my paper very damp, only slightly moist, which can help prevent cupping. IMO, 24 hrs in the bender isn't needed, once it back to room temp, it is what it is...

Thank you

I use a Fox style bender with stainless slats and a silicon heating blanket. The sandwich is (starting from the bottom) - slat, kraft paper, wood spritzed with water, kraft paper, slat, blanket. I stick a digital thermometer between the blanket and top slat. I usually start the bend about 300 and let the temperature climb to somewhere between 350 and 400. I leave the side in the bender overnight if possible, then into the mold. There is a little spring back but not much. I've bent at least a dozen sides, broken one (took a seminar with Charles Fox and watched him break one too)

Those are the instructions that John Hall included with the bending machine. It sounds like you aren't getting hot enough.

I’ve made my bending forms with about a 1/4” over bend in the upper and lower bout to help combat spring back.
If the waist doesn’t get close enough I take it to the pipe to bend it the rest of the way.


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When are you starting the bend? The most common issue we've seen is initiating the bend far too late, and after the water in the bending package is largely exhausted. If you wait for the temp to rise much above 212 deg F, the wood will be too dry to take the bend and set. Consider starting the bend as soon as visible steam begins to rise from the package. With a bend started at the waist (bring it down to 3/8" or so off the mold), then lower bout, then upper bout, we see little or no spring-back in mahogany, anigre, ash, etc., while rosewoods are always net shape.

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