Acoustic Guitar Construction

Peter, I build mine with wood spreaders and have had great performance.

I used 7-8 spreaders total and position them carefully so they are just tangent to the curves - careful not to let the square edges of the spreaders stick above the outline of the body - no bumps/humps in the bends.

I also use a silicone blanket for heat, and sandwich the set with steel on either side. This means my bending forms are fine being just wood and wood screws.

IF you are using light bulbs inside your bender to generate the heat, then a metal wrapped/jacketed form would be wise.

I use the bulbs in the base. Inside of the form is covered in aluminum tape. I've switched to using 1/2" wood dowels covered with aluminum tape. Have not noticed a difference from the aluminum rod I had used on the first couple of forms. All my forms are covered in sheet aluminum. And pre bend the waist.

here it is on cad