Cracked EIR fox bender

[Mike Ryan]

Hello,
its been a while.
Trying to bend some east indian rosewood. Sides were brought down to .085. Used homemade classic Fox bender, om profile, silicone heating blanket. Bend at 350 and wetting the sides times 2 then wiping off. Brought down waist slowly, then large bout, then small bout slowly. Still got this cracking in what appears to be sapwood. Double heating gave me a good profile with little spring back.
Wonder why and if there is any salvation for these sides. Cracking is in the same place on the other side. Bent some anigre in the same mold without problems.

Thanks in advance.

[Mario Proulx]

Since it broke in the same place on both ribs, and other woods have bent well for you, I suspect the wood itself had hairline cracks and/or other invisible weaknesses.

Happens...(unfortunately)

[Michael Lewis]

I would look closely at both sides to see if the fractures mirror each other, if they do it is as Mario suggested but if the cracks are just in the general area and not a mirror then I think the "sandwich' of metal and wood was not snug and possibly not hot enough. It is important to force the metal leaves together so the wood and blanket are snugly captive. This makes the wood form into the shape you want and keeps it from rippling across the side as well as helping prevent cracking, but it must be hot enough to soften the wood. EIR generally bends very easily.

Did you hear any cracking when making the bends?

[Mike Ryan]

I did not hear any cracking but could have missed it.
Any way to salvage these ribs?

[Doug Shaker]

Repair, hmmm. If you have side mold, you might be able to laminate something on the inside. The combination, glued together, might hold a good curve. I don't know what else you could do.

[Mario Proulx]

A lot of suppliers will sell you EIR sides only if you ask, for very little money, so it's not worth trying to save these. Call Allied Lutherie, StewMac or LMI and tell them what happened, and ask if they'll sell you a set of ribs only.

You'll put in a lot of time trying to fix those, and even laminated, they'll still be prone to give you grief a year or two down the line, in the form of finish cracks or other bugaboos.... Just replace them.

[Pat Foster]

Mike,

If you send a piece of these sides to a supplier, they might be able to get a close match on a replacement pair.

Pat

[Pat Foster]

Make yourself a narrow stand about 6" tall notched to straddle your bandsaw blade, and cut a bunch of pre-bent binding out of the good part of those sides.

Pat

[Clay Schaeffer]

If the sides have not been cut to width you might lose most of the cracked area when they are. There are a few tricks to increase the width of the sides that remain. A parlor guitar using a narrower side set and might be another possibility.

[Mark Swanson]

You could also build an Octave Mandolin or Bouzouki with them.

[Mike Ryan]

Yes, the crack is in the same place on both sides.
All great suggestions. I had not thought of the one to make binding out of them. I kind of like the look of plain bindings sometimes.
I am going to send some wood for resaw at lmi so i might send along the back for a match. Good idea, Pat.
I will say that bending with a silicone blanket is hard for me but I think it could be that there are so many ways out there to do it and think about 1/2 of them are in error.

[Michael Lewis]

Many tasks are difficult to master, but once mastered they seem easy.

[Mario Proulx]

And there's a reason it's called "mastering" the task; if it were simple, everyone would be doing it. <g>

Practice sides are a good idea, even if they are mystery wood. Practice bending everything you can get your hands on....

Here's a quickie video of me bending some cocobolo. I preheated the entire assembly for roughly five minutes prior to starting the video; you -did- preheat everything in your bender, correct? If you don't preheat, the upper slat will be cold; the only way to get heat on both sides of the bend is to get the upper slat good and hot(as well as using a slat that is heavy enough to hold the heat through the bending process). My slats are .022" stainless steel.

http://youtu.be/sUJbB0pa7Zs

Edit: notice that I use my hands(in heavy, insulated gloves!) to press the upper slat tight against the rib when bending, and that I am only bending where my hand is, such that my hand supports the bend. Also note how I allow the bend to relax a bit every few seconds. You have to be quick(to avoid the upper slat cooling too much) but you still need to allow the wood time to re-organize its fibers as you bend, and part of that it allowing it to relax a bit. I don't believe in the cauls and springs and all that a fox bender uses, as you're more likely to have unsupported areas, and the tactile feedback that I get through my hands and ears tells me when/if I need to ease-off and when to go ahead; this is where experience and practice comes into play....

[Mark Tierney]

It looks like a compression fracture, and probably happened in the tree. Had it been caused by bending technique, the surface we see, being in tension, would show long splinters at the break instead of the squiggly little line of a hairline fracture.

[Rodger Knox]

It can be fixed, I had a bloodwood side break like that. I wouldn't recommend fixing it, the repair is much more difficult than starting over and the probability of a satisfactory result depends on better than average repair skills. The guitar I fixed will be mine forever, the repair is not good enough to let it go.