Official Luthiers Forum!

I'm building my fox bender. The LMI plans call for an aluminum bar that lies under the sandwich and goes into the bottom of the form. The bar is attached by springs to the press. How important is this? Would the bender work as well without?

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

It's purpose is to apply pressure at the waist to prevent it from cracking. It is most important for figured woods, but you can get by without it for non figured woods

_________________
John Ressler

I did not add it to my recent foxbender and now wish I had. It really does add some support to the bottom of the sandwich while initially bending the waist. I end up using some close pins to hold the sandwich closed in that area until it is to the point of getting in the way.

THe bar pulls up under the sandwich giving that added support to keep the sides from fracturing.

I almost wonder if this would have helped in my cutaways too...

Joe

_________________
Joe

I might be missing something here but do you mean the removable bar (or on a Blues Creek bender a bolt) that goes through the sides of the bender and the bending form? If so this does nothing more then keep the bending form centered under the waist caul - which is critical I would add.

Sorry but I am not sure I understand what you mean.

Some of the FB style units have a flat bar that helps center the form in the jig but also have springs attached. This bar is in a slot that allows it to be pulled up toward the stack. Once you connect the springs to the bar that attach to the uprights, it pulls the sandwich upwards while the caul pushes the sandwich downward. While the sandwich is up in the air (as opposed to laying next to the form like at the upper and low bouts) in the waist area, the sandwich has a tendancy to open up a little. The bar keeps the stack tight which reduces the chances of fractures and facets. John Ressler was explaining that to me....and from what i understand he worked with Fox...the man. When I built my unit that does not have this feature, one area I had trouble was keeping the stack tight at the waistline. Having this bar/spring set up would no doubt have eliminated this problem.

Joe

_________________
Joe

No there is on the Fox design an aluminum bar that is tied to the waist caul with springs that goes under the sandwich and engages into a slot on the form when you get close to the form. It both keeps the sandwich tight at the apex of the waist bend prior to engaging the form and acts a centering device on forms that are not secured with a rod or bolt. Many of new designs have eliminated this in favor of a stretched taught sandwich or a clamped as needed supported sandwich. I have not used the bar method for several years because it just did not seem needed if you keep the sandwich clamped tight or pulled tight. The intention was to eliminate the gap that wants to form at the apex of the bend between the bottom slat and the wood as you approach the form.

Hesh its the aluminum bar under the sandwich that has hooks on the end. Its connected by springs to the sides of the screw press frame. The reason I ask is some benders such as the Everett bender sold by LMI do not have this bar.

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

I did not know this - thanks! My Bender just has a bolt that only pulls out but not up.

??? scratching my head bolt tha tpuls up????? The bar is part of the waist caul mechanism not the form. It fits into a slot on the form as the bend gets close to the form. Most folks have abandoned this

Here is a photo of the bar with springs. This is as designed by C Fox, which I copied (with his permission of course) When I took his class a couple of years ago, he explained the purpose to be to apply pressure at the area most vulnerable to cracking - the waist. The process - 1. Screw the caul down part way until it makes contact with the "sandwich" 2) attach the springs to the bar, which brings it in contact with the sandwich 3) screw the caul down within 1/2 to 1 turn 4) bend the ends 5) complete final turn at the waist

Again, if you aren't using figured woods or bending sides for a dreadnought, it probably isn't necessary. I have found it to help considerably on more figured woods, tighter bends and on brittle bindings - such as ebony.

_________________
John Ressler

I studied with Charles Fox in 1977!
We used the bender then -and i do now with the bar in place.
It pulls the slats tight against the wood-so there is less chance of tearing or breaking!!!
I've never cracked a set with that in place-
Think about it!
The metal slats act as a support for the wood that wants to let go!
or as another layer of wood -to help keep the wood from splitting!
The springs pull the bar up to the lower slat and apply pressure so the wood will be less likey to split!
I've bent many highly figured sets on mine-also if I need to do any hand bending I put either a wetted veneer(.028) or metal stock
on the convex curves!!!!!!!

Mike

_________________
Mike Collins

The bar works as an alignment device to assure the waist is in the proper position. We at Blues Creek Guitars. use a pin to locate the waist and let the pin locate the pattern in the press. I find the pin holds the cutaway side more secure.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

John is the bolt sprung? What keeps it up against the sandwich?

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

Rich, I am not sure who's pic this was, but here it is with the sandwich in place and the spring pulling it up tight. I think this picture has the waist caul allready set 100% down, but imagine how the bar would pull up as you unscrew the waist caul

_________________
Joe

OK you guys got me curious so here is one of my forms. As John said a large bolt goes through the bender sides and the form and keeps the alignment with the waist caul.

But what I am learning in this thread is that the bar style provides support under the stack at the apex of the waist bend, where support is really needed. And the springs are intended to pull the bar even snugger against the bottom of the stack.

Looking at my bending form it looks like I could retrofit this idea and add some springs.

It also looks like notching the bending form would be a piece of cake on my band saw with the form on it's side and doing both sides at once and then using a sharp chisel to do the bottom of the notch.

My question is in the bending sequence when do you hook up the springs? Before the last 1/2" of the waist caul is lowered?

Thanks!

Hesh there is another view if the bar on page 108 of the new LMI catalog.

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

When you start off bending sides, the sandwich is not supported from underneath. There is a gap between the form and the metal slats. Once you connect the springs to the bar, it pulls the bar up under the slat to support the bend. As you crank down the waist, the bar goes downward back into the grove...but will add some tension as it goes.

As some have stated here, in some cases, it is probably not needed...and in some cases it nice to have. If your building a new jig, you should consider adding it just in case.....your uke sides would have benefited from it in the first place. Really the only difference to building a FB with it (as long as you use the sloted stand-ups) is cutting a groove in the form. My FB used channels instead of the grooves or slots so I could not add it.

_________________
Joe

Hesh, once you start adding downward presure to the waist the stack will want to open. I would say a few turns into the process would be a good time. The other thing that makes a difference is the shape of the waistline. The archtop I just did has a deep waist. So when the side wood material is resting on the upper and lower bouts, there is still about 3 inches for the side wood and caul to travel downward.

here is a pic of the waist that would have benefited from this:

_________________
Joe

You are right Joe, looks like its worthwhile doing the bar while I'm at it.

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

But I think I will go Kathy Matsushita's way with the cutaway bender. She uses a separate form for bending the cutaway. You can see it at her site.http://home.comcast.net/~kathymatsushit ... /atc4.html
I have some curly koa that I just can't take a chance on.

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

Here is how we built ours...and we could not add the tension bar. The next one I build will include it on the waist and the cutaway areas for sure.

_________________
Joe

BTW: I think I saw a picture of Todd Stocks setup where he made a seperate form for cutaways that also fit in the fox bender. It looked funny at first, but basically it just bends the 5" long side piece that fits the florentine cutaway. I think Kathy did hers with a seperate clamp and jig IIRC.

Joe

_________________
Joe

Joe has it right!
I heat mine so water bounces off the slats!
I sprits the wood (with water) and of course I've marked the waist with tape and a visible marker-
Then I slide the sides in-I line up the center of the waist and attach the springs to the aluminum bar-then slowly crank the wiast down!

The springs pull the slats up against the wood!
They act as another layer of wood if tight enough so the side will not split easily!!!
The I do the upper bout-then the lower!
Never had a failure!!!!!


Mike

_________________
Mike Collins

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.

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