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Joe and Rich my friends I understand now. The slots in the bender's sides match the slots in the bending form so the bar is lowered into place during the bend supporting the stack from beneath all the while. The lower the caul is the tighter the springs get.

This looks like an excellent idea to me and cheap insurance. I'll have to check the slots in the side of my bender and see if they are a size that I would work with. As you can see my bending form provides no support under the waist......

Many thanks!

Hesh, I have the old LMI plan for the fox bender. It calls for 1/4" x 1" aluminum stock for the center support bar. I'm not sure of the springs, the plan doesn't give sizes for them.

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A higher purpose for wood.
Rich Smith
Issaquah, WA

Hesh, my friend...yes you understand it correctly now. It is so hard to describe something in words that simple pictures could have done much faster.

I have learned a lot over the last few weeks about these benders...I wish I had know this stuff a month ago. Ha ha. I have probably bent a dozen sides in the last few weeks trying to understand the engineering side of whats going on. That is the bad part of being an engineer as my day gig. I need to understand even the stupidist of things! Ha.

J

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Joe

We used very strong screen door springs for ours. We just cut them down to length. There is a lot of tension on them. I see some large 1" diameter springs, but honestly the 1/2" heavy duty springs we have seem to work great. We bought them at HomeDepot or Menards. I think there was two springs per package for about $3 or so. Just check to see that they are the heavy or strong version. I think it may be listed in pound/pressure.

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Joe

What I do not like about Kathy’s for is the fact that if you are not very carful the sharp corner at the apex of the horn adds a lot of stress at a singular point on the apex of the horn at the same time the return of the cutaway radius is engaging. I assume she has to keep pulling on the sandwich to keep a buckle from forming at the horn. I could be wrong but that is the way it appears to me.

I had much rather form a bend at a time rather than try to form two bends at once.

Michael, don't you have the same issue with the fox bender with cutaway caul?

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A higher purpose for wood.
Rich Smith
Issaquah, WA

Not if used right, You should as I posted in a differnt thread last week manintain the caul tangent to the horn first and allow the caul to work its way around the horn and down into the cutaway valley. Not just plung straight into the cutaway valley and even if you do a plunge bend instead of following the form around the horn bend there is never a sharp singular pointed surface in contact with the sandwich using a press caul the caul is round no sharp edges

I wonder if Kathy's jig can be modified to address your issue?

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A higher purpose for wood.
Rich Smith
Issaquah, WA

Dang how I love my Doolin style bender

None of those centering bolts or modified bending forms or waist clamp bars..... just a couple of springs and a lot of tension on both sides of the sandwich during all bends.

I think the original question has been answered already, 1st purpose, tension for bending the waist, 2nd purpose, alignment of the sandwich.

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Rod, got a picture of one (Doolin bender) ? Its not too late for me to modify my plan.

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A higher purpose for wood.
Rich Smith
Issaquah, WA

Richardo, here you'll find my post about the Doolin style side bender I made.

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My Facebook Guitar Page

"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

Thanks Rod. Seems we have a variety of opinions as to the necessity of the center bar. Your bender looks alot like the one I use for ukes. Except I found the screw down for the waist too time consuming and converted to a screw press which I really like.

_________________
A higher purpose for wood.
Rich Smith
Issaquah, WA

Joe
It's not too late to add it to your jig. Just cut a slot in the sides of the jig and the top of the form.

One very important item not noted yet - the aluminum slot must be perfectly flush with the top of the form, or the caul at the waist will push that area below the top of the form and crack it - defeating the purpose of the bar in the first place

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John Ressler

I used the bar thing at another shop and now use one without it (one of John's) and have not found any difference in bending or when taking rims out of bender. One way works as well as the other. I do prefer the use of triple form when bending rather than just two. Other than that just a like Ford or Chevy (or to be PC, which I hate PC, add your favorite green car) arguments