Making Forms for Fox/Universal Sidebender

[Larry Schultz]

When I make a new form for my sidebender, I undersize it by the thickness of the sides, and usually have to touch up the bends on a hot iron. But I'm wondering if anyone exagerates the contours of the form, in the waist and at the ends, so as to minimize the "springback" effect, and if so, by how much? In otherwords, can the waist be made a little deeper, and can the ends be "undercut" somewhat so that when the side is removed from the sidebender, it is closer to, or dead-on, to the plantilla's shape and thereby reduce or eliminate the need to touchup the bends on an iron? Or is this just asking for trouble?
Any insights are appreciated!

[Bob Webster]

I prepare my bending forms for my Fox bender the same way you do, with no compensation for springback. The reason is because each set of wood is going to respond to the process a little differently. I just bent up a set of East Asian rosewood (D. bariensis) that went into the assembly mold with no touchups. However, the set of East Indian rosewood that I ran through the bender previously required substantial touchup. I concluded quite some time back that I could end up chasing my tail if I tried to compensate for springback. BTW, I use both the lamps (does a better job at the waist) and the silicon heating blanket.

[Ronnie Nichols]

I have a home-made bender similar to the Fox. I built my dreadnaught bending form just exactly as you suggested. My sides are overbent a little. They are probably exagerated by 1/2 inch or so at the ends and not quite as much at the waist. It has worked out fine for me with no problems. I've built 6 dreadnaught guitars with it. After the neck and end blocks are glued in, it seems to me that the side form holds the shape until the linings, back, and top are attached. I think I'd rather have the sides overbent as underbent. This is just my little 2 cents worth. I'm sure others may have a different idea.
Ronnie Nichols

[Doug T]

Ronnie, I agree. I've got a homemade bender that each form is just a touch over bent on the ends. The only wood that really didn't hold its shape well was a curly bubinga guitar with a tight waist. Yow that stuff is like spring steel. I also line the inside of the forms with aluminum foil to reflect as much heat (I'm using the ol' 300 watts of light bulb method) and once I did that, it seemed to improve the action of the form.

[David Houchens]

Do you heat them, then leave overnight, then heat again? Someone suggested this to me once. I don't leave overnight as I've not hade enough springback to be a big problem. It might help set the shape. I did build a hollow form I store them in until I start to glue but they still spring a little. David

[Larry Schultz]

My thanks to everyone who has replied on this topic.

When I posted these questions back in September, I found out the next day that the discussion had been "deleted" with no explanation as to why, but I see it's now back on the forum. Interesting.
Anyway, I made my new form with a deeper bend in the waist, about 1/4", and I undercut the ends of the bouts by about 5/16". The waist bend came out right on the money, but there was still some springback at the ends. That's acceptable to me, as I find it much harder to rebend the waist without throwing off the bends in the bouts than it is to have to touch up the ends.
I find I can minimize the springback by 1) making sure the sides are throughly wet by sponging with water until they don't absorb any more, 2) getting the form up to a high temperature by closing everything up with the metal slats in place and running the light bulbs for at least 10 minutes before adding the wood sides. I've only been using the light bulb method so far, but I think a silicone blanket will probably work faster and provide more even heat. 3) making sure the wood in the waist area is good and hot before running down the screw. I monitor the interior temperature of the form with a digital pyrometer (massive overkill, but it's left over from my HVAC days; a dial thermometer with a 4" stem, like a cooking thermometer, works just fine too), 4) letting everything stay heated for about 10 minutes after the bending is completed (watch that interior temperature!). I have forms that are lined with aluminum foil, and some that are not. I can't say I've noticed much of a difference either way. I leave everything to cool in place for a couple of hours then reheat the package up to temperature again and then go through another cooldown. I either put the bent sides in the mold (touch up bent if needed) or just leave then in the bender until I need them. I'm thinking some touchup bending is inevitable, but I think I've got the majority of the bends about right now, and some minor rebending at the ends isn't a big problem.

Thanks again to all.
Larry