Sizing a side-bending Form

[John Scime]

Im starting off (slowly) on my first build - an L00 replica.I have a Blues Creek side bender that I purchased a while back, used, with a dreadnaught bending form. I intend to build a new form for the L00.

Building the outside building form from the plan I have is easy enough. But I wonder if the inside form needs to be adjusted or reduced to account for the thickness of the side? In other words, should the inside form be roughly 3/32s smaller than a line traced from the outside form?

Please give me your insight. And thanks in advance!

John

[Barry Daniels]

Yes, it should fit the inside surface of the sides so it needs to a bit smaller.

[Marshall Dixon]

...In other words, should the inside form be roughly 3/32s smaller than a line traced from the outside ...

That's what I do, but make it 1/8" to account for the sheet steel in the bending sandwich.

[Barry Daniels]

And you may want to add a bit more for the heating blanket if you use it on the inside of the wood instead of the outside.

[John Scime]

Thanks, as always!

The wisdom and experience of this forum is second to none!

Js

[Bryan Bear]

I'll openly admit that when I take sides out of the bending machine, they are never perfectly in the shape of the bending form or the inside of the mold. There is always going to be some degree of pushing the sides into the mold be it from a small degree of spring back or slight inconsistency in the offset shape of the form or other factors. So with that in mind, yes, I make my bending forms smaller than by mold but I do not worry so much as to say that I downsize it by 0.085" plus the thickness of my bottom slat, the paper and foil I wrap the side in. . .

when I am making a new shape, I make an outside template for the mold and get it how I want. Then I make an inside template and sand and or rasp it to as close as I can get to a good fit. Then I use a router bit with a binding bearing to make my sheets for the bending form. I think I use the one for a 0.10" but I might actually make it more than that, It has been a while. It doesn't have to be perfectly engineered.

[Clay Schaeffer]

When I make a new set of forms I will cut out both the inside and outside form from the same piece of plywood. I draw the outline on the form, carefully cut on the line with the bandsaw and use the inner piece for the bending form and the outer piece for the building form. The band sawed line is sanded on both pieces and this helps create the size difference needed for the forms. As Bryan mentioned, tolerances are not extremely critical, close is good enough.

[John Scime]

Thanks, Bryan and Clay. This discussion has been very helpful! I think I'm ready to go now.

Cheers. Js