Bending Form Spreader Rods question

[johnnyg]

One thing I am not sure of is how to size the bending template. My plan was to trace the inside of the mold I got from Ken as as starting point. If the sides are going to be about .075" thick, should the template be reduced in size by the same amount? If so, is there an easy way to get this done accurately without the use of a CNC router? Am I going about this all wrong?

Also, I would like to make the waist pipe bender using your design, but I don't have a heating blanket. The luthier supply houses are pretty expensive. I checked with Watlow and Omega and they don't have many in stock any more and not in the sizes I need for waist and full side bending. They want a 10 week lead time to get them for me. That is too long of a wait before I can progress on this build. Are there any other suppliers of these blankets that you are aware of?

[ken cierp]

My plan was to trace the inside of the mold I got from Ken as as starting point. If the sides are going to be about .075" thick, should the template be reduced in size by the same amount?

Don't worry about it

I don't have a heating blanket

There's a suitable blanket on Ebay for little $$

[johnnyg]

Thanks Ken, I will definitely confess to worrying too much. its details like this that trip me up.

I located the 4 x 6 blanket on Ebay and picked it up for $20! Thanks for the push in the right direction.

[peter havriluk]

Putting holes in aluminum sheet:

Ken mentioned nailing a layer of aluminum sheet to the mold.

To make the attachment holes in the aluminum sheet, I have a suggestion that I think will do a better job faster and more accurately than drilling through sheet, which will leave burrs on the holes that would be best chamfered or hammered down. Get hold of a 'Whitney punch' set or one of its many clones and punch the holes. Super quick, doesn't need an alignment punch to center the hole, and leaves a nice clean hole that doesn't need any more attention to be usable. Just mark the holes with a magic marker and punch away. And this tool is useful in a zillion ways, once it's available. Easy to put a hole in felt or leather, for example.

[ken cierp]

Power punches are indeed cool tools -- do they make dies for such a tiny hole #54 drill size is what I use for the recommended nail size 18. The economy Whitney sets I've seen have 1/8" as the smallest.

[peter havriluk]

Smallest Whitney brand punches I've used have 3/32" in the sets that come with the punch handle. The Taiwanese Neiko set I looked up before posting my comments also bottoms at 3/32". Never had a use for something smaller, never looked for one smaller. Just looked at a drill gauge/decimal inches table, #54 is .055", 3/32" is .0938".

[GlennH]

One thing I am not sure of is how to size the bending template. My plan was to trace the inside of the mold I got from Ken as as starting point. If the sides are going to be about .075" thick, should the template be reduced in size by the same amount?

The approach I'm taking, with encouragement from local luthiers, is to work as you have done with a form based on a tracing from the inside of the female mold. The only thing I'd change from that would be to tighten the neck and heel end a little - like at most 1/4 inch - to anticipate springback. Perhaps drop the waist 1/8" or so for the same reason. Don't overthink it.

I'm experimenting with heavy steel mesh over the form to provide lateral support for the wood to keep it from rippling. We'll see how that works. Heat is coming from silicone blankets, not from inside the form.