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I seem to have had a run of bending issues. Seems if the genus is Diospyros, things go awry. On my current baritone project, I wanted to do a Florentine cutaway, something I've only done before with Indian rosewood, but this time it's with Macassar ebony (didn't help that I chose a set with sides only barely long enough).

The first side came out of the bender Ok, although there was a hint that some faceting was beginning at the edge of the upper bout bend -- easily sanded out. For the cutaway side, I did the main side piece up to the point just fine, cut off the recurve section flipped it and started its bend on the mold in the bender near the upper bout curve. That's when things started to go south. Came out with lots of facets and not much curve, although the show face looks OK.

On to the electric pipe, the wood just doesn't want to relax, and the existing cracks make it move unevenly. It's 70 thou thick, 1.8 mm, but I can't thin it more in it's current state. I can see I'm just at the point of scorching, but doesn't relax. So, what next?

Plan A. Soak the cutaway section in a pot of hot water and hope that a lot of moisture in the wood will help it relax on the pipe. (So far I've only spritzed lightly). I fear it will go all wavy, but I don't have much to lose. If I can rescue it, I'll be much relieved.

Plan B. Dig out another set of Macassar and use new sides for a second attempt. If the back and top weren't already cut and braced, I'd scrap the cutaway idea, but I'm kinda committed now! I fear a second attempt might not go much better and I'll have ruined yet another set of expensive sides.

Plan C. Dig out a set of IRW, expecting greater chance of success bending that, as it's not been a problem in the past.

I guess I'll start with Plan A and see where it goes. The guitar is not a commission, so no real worries about a commitment to anyone if I change B/S woods, although the aesthetics are skewed. Other ideas?

I went my first four years of building wondering why folks made so much fuss about bending. Of course, all but one guitar in those years was IRW. But since then I've struggled cracking ebonies in general and jarrah, and managed to overheat a black heart sassafras side to point of charring! May have to import some SuperSoft for future non-IRW builds!


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You're not alone. Here's the result of my attempt at bending flatsawn Malaysian blackwood http://www.luthiersforum.com/forum/viewtopic.php?p=620475#p620475
Fractures and splits and ripples and kinks. By blind luck I got the waist in an area that relaxed and bent with ease on both sides. But the tail area was extremely determined to cup, and the shoulder/cutaway area didn't want to do anything at all. I was working at .05-.06", so thickness is probably not the issue. It's more a question of exactly what conditions will make it relax. A wet paper towel on the pipe seems to help a lot, but the added moisture is what caused such extreme cupping. But if your set is quartered, then that shouldn't be as much of a problem. But the cutaway never fully relaxed with the towel either, so I don't know what to do with a piece like that.

Another option is to look for some matching macassar veneer. Either make the cutaway piece out of EIR or something and veneer it, or just use a stack of veneer slices.

How hot are you bending? Ebony wants a lot of heat. The only way to salvage it is to build a Tony Karol cutaway bender. It's worth the effort. I don't have pictures of mine, but here's a photo of Tonys. It works very well.

http://luthiersforum.com/forum/viewtopic.php?f=10101&t=26950&p=384713&hilit=Cutaway+bender#p384713

Some helpful ideas here -- thanks guys!

I'm aware that ebony requires lots of heat, having struggled with many ebony binding strips. On a previous Malaysian Blackwood build I dodged a bullet in the bender, but the very edge was trying to fail (later removed as a binding channel).

In the bender, my digital thermometer was showing about 275°F when I started to bend, and then up to 325°. But, with the slight reverse curve in the cutaway piece (cut from the main side and flipped to match grain), the contact between the slat and the wood was not good -- I suspect this was part of my problem and I simply didn't get sufficient heat transfer as I started the bend.

I decided to start down Plan A and threw the piece into a pot of water, brought it up to the boil and then let it steep. It was when I saw the figure pop in the water that I vowed to do everything I could to rescue this gorgeous piece of wood, rather than abandon it. In the hot water, the piece relaxed and became almost straight again!


I tried again on the pipe, but it didn't feel any different. It's now clamped flat between straight slats at right angles to dry more completely. The cracks on the outside curve surface have virtually disappeared. I think I'll be able to thin the piece further in the sander.


I could thin the ebony to, say, 35 thou, back it with an inside piece of IRW, and try to bend both together in a Karol style bender? Then laminate the two pieces with Titebond when cool? I'm not sure if I should wick CA into the crack areas prior to bending, as my experience is that CA repairs fail and expand under very high heat.

With my IRW Florentine guitars I've been able to get a good joint at the point to avoid having to bind. I like the look of the matching grain lining up at the point and it will look particularly striking with the Macassar. If I can't pull it off, then binding the tip is always an option.

I'll cobble together a dedicated Karol-style Florentine bender tomorrow. Other ideas and suggestion s on how to proceed are welcome!

How the heck do folks bend ebony into Venetian cutaways without failures?


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I agree with David's suggestion that you use sufficient heat with the Macassar. Also, as you thought, thinning the wood before bending then laminating an inner veneer is a good strategy. I've included a shot of my bending jig--a little less sophisticated than Tony's. Essentially an inner and outer caul with enough space between to accommodate the wood, heating blanket and a steel 'backstrap'. I bend at a maximum temp of about 310. This set up has even worked with black locust, which was even more resistant than the macassar.



[url=http://s1198.photobucket.com/user/highdrawlicks/media/IMG_0191.jpg.html]

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michael propsom
www.propsomguitars.com

Regarding thinning the wood, I've found that with my set up, the macassar bent fine at .060. I don't know if you really want to go down to .035. But, you have to do what makes you feel comfortable.

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michael propsom
www.propsomguitars.com

My side is thicknessed to .070". I wet down the side and put craft paper on both sides that is also wetted. This is sandwiched with foil and into the bender, clipped to the heat blanket and steel. I turn up my bender to 500,when I see steam, I start the bend. When the bend is complete, I turn the heat down to 310.

Wrapping ebony in foil really seems to help as it holds the steam in during the bend and cook process.

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No. I don't wrap it in it. The edges are open. It's there to prevent the spring steel from discoloring the wood. You want the steam to be able to escape otherwise you'll be cooking it forever to set the bend and dry it out. The craft paper helps keep the wood wet.

David: The damaged cutaway section is now flat and ready to reduce in thickness as I like. I've made a good start on fabricating a cutaway bender that will handle both my OM and MJ models. The form is finished (laminated 2x6 spruce) and I've cobbled together springs and other hardware ready to assemble.
Because the location of the point is critical (matching as close as possible the main side section), I've organised the mold to to start the bend there and proceed to the heel. Question for you on your sandwich in this bender: Sounds like our sandwich is similar -- I also use wet kraft paper, but no foil as my slats are SS. On my Fox-style side bender, my assembly, from top to mold is:
Slat
Blanket
Slat
Kraft paper wet
Wood
Kraft paper wet
Slat
Mold

The sandwich is clipped together and everything moves together , slipping as required when bending. My thermocouple is located so that the wood is between it and the blanket, so it reads temperature of the wood, not the blanket.
All sound good? Or do you/Tony use fewer slats or perhaps a permanent slat fixed to the mold?
I will do tests with two pieces of 50 thou rosewood to see if they bend properly together. If so, I'll thin the damaged Macassar and bend it together with a piece of rosewood for later lamination.
I had hoped to have this body closed by now, as I have to travel much of the next two weeks. Guess it will be closed when I get back.


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I've done a sandwich like that before, but didn't find I gained much from it, but it won't hurt either, just makes it harder to bend the sandwich. I use a unitary blanket that has a built in thermocouple. I don't know that the thermocouple is going to read the heat of the wood, as the heat transfer from the steel will be read long before the wood gets to temperature. Listen, and look for steam, then start your bend, slowly. Don't fear bending really slow, as in several minutes to complete the bend. Look at Taylor's videos of their benders and how slowly they move.

I'd also shoot some CA into the cracks before you bend it and clamp them home. They may still open up when you re-bend, but it'll help stabilize it. If they open, clamp them down with a 1/4" x 1/2" piece of UHMW plastic caul and hit them with CA. Work your way through all of the fissures.

Very helpful, David -- thanks!
What slat(s) do you leave out? The middle? The middle AND the bottom?
Cracks have been CA'd. The piece will be left dry and flat in a ventilated press 'til I return from my trip.
I know I've been bending faster than I used to -- time to take it slow.


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I just use an inner and outer slat.