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I'm building up steam (slight pun) for bending the sides of my next guitar and I'm a bit paranoid. The wood is some stunningly figured coco and I just want to make sure I've covered all the bases.

First, I have never used Super Soft for any sides and everything (knock wood) has gone well. Should I consider it here? I checked a couple of online sources, it seems to range from 9 to 12 bucks a bottle, but by the time I added shipping and some handling fees it was well over 22. I guess I have a little problem paying more to ship something than the cost of the product itself. But if I need it.,..

I use a Fox bender, wood is thinned to 0.090, it's a simple OM shape with no cutaway. I normally put brown kraft paper next to the slats - will the oil in the wood give me any problems? Is the oil a problem with Super Soft? Recommended bending temperatures (240 to 300 F?)?

I think I've got my other coco concerns covered (I'm faithfully wearing my dust mask) and I plan to wipe all the glue seams with acetone (I'll be using Titebond for the seams). Long range plan is to pore fill with Zpoxy and finish in either nitro or KTM-9, but for right now I need to bend some sides.

I just bent 2 well figured sets of cocobolo but I thinned to .050" and laminated them. No trouble to bend at all. Didn't need Super Soft. I wrap in brown paper as well as foil. The paper will suck a lot of oil out of the wood and makes cleanup a breeze. Super Soft will change the color of the wood but if you stay as thick as you are now you should be able to sand the discoloration out. I do highly recommend laminating sides, especially with figured woods. It makes them much easier to bend and the lams are stiffer than the solid wood by itself.

There is some good info on using Super Soft for bending sides in this thread: http://luthiersforum.com/forum/viewtopic.php?f=10101&t=48694&hilit=super+soft

Some of the posts there specifically address using it on cocobolo.

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There is no consensus that wiping the joints with acetone is a good idea. Many feel it just brings oils to the surface...

I’ve built several of coco, most of it figured and they all bent like butter.

I just bent a set for a Tenor Uke and a set for a dred. I bent the dred at 80 and the Uke at 65. I used supersoft on both. I sprayed it on and let it sit a few days.

Bending procedure is slat - blanket - foil - butcher paper - side - butcher paper - foil - slat. I bent at 290 degrees.

Zero spring back at all and they both bent very easily.


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"but by the time I added shipping and some handling fees it was well over 22. I guess I have a little problem paying more to ship something than the cost of the product itself. "

But what did the cocobolo cost you?

Cocobolo doesn't usually pose too much of a problem if it is thin enough, but an OM has a fairly tight waist, so if you feel you need an "edge" the SS might give it to you. What type of figuring do the sides have?

You should be fine, I'd go .080 on the sides. If you have cut offs from trimming do a test bend.

There are three concerns with cocobolo when we build with it in this shop - the incredible amount of resin that is shed, the color change seen at higher temperatures, and gluing. The first concern - all that resin! - can be addressed with using wet butcher paper as discussed in previous threads...most will end up being absorbed into the paper as the bend progresses, so a good deal of cleanup is avoided. Lower peak bending temperature will also deduce the amount of resins dumped...

The issue of color change is best handled by planning for lower peak temperatures during bending and doing to the back what is done to the sides. Coco only requires 250-260 degrees F for even highly figured stock to bend without any help, and the higher the temperature used, the greater the oxidation of the resins and the more color change seen versus the back. We use our standard bending stack (slat, foil, wet paper, wood, wet paper, foil, slat, blanket, slat) and begin bending as soon as steam is seen being generated, then throttle down the blanket as soon as the bend is set and dry at a lower setting (220-225 deg F) for a little longer (50-60 min instead of 30-40 min). The back is stickered and weighed and is baked at the same temperature as the sides for a similar duration (about an hour at 230 deg F seem to avoid too much stress and resin cleanup), and comes out matching the sides far better than if untreated.

We have used cocobolo bindings on a few recent guitars, and handle the bending in the same manner, ensuring that we bake the tail graft and handle any Venetian or Florentine trim in the same fashion as the bindings (heat to ensure the same color change). In general, the lower the bending temperatures, the less color change and less resin seepage is seen, so we err on the side on more moderate temperatures than the 300-320 deg F we might wish to see with some harder-to-bend woods like curly anigre.

On gluing, we keep in mind that oxidation of the surface of the wood reduces the effectiveness of the chemical bonding provided by both hide glue and Titebond, so a freshly planed, scraped, or sanded surface provides the best chance of a good bond. Even a few hours between jointing and glue-up can adversely effect bonds in cocobolo, as can be seen by how rapidly a freshly planed or sanded piece of cocobolo will change color.

Because the resins in cocobolo are soluble in both water and in hydrocarbon-derived solvents such as naphtha, using either or both to try to clear the joint of contaminants may not do much else besides more evenly distribute those resins. In the past, we have used both epoxy and urethane adhesives to join cocobolo backs, but have not seen any advantage over fresh hide glue or Titebond on a freshly prepared joint. For other joints, scraping and sanding just prior to gluing seems to offer the best strategy to keep things together.

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Woodie, are you baking the back at final thickness or leaving just a little extra on for safety? What are your thoughts on putting SS on a back to match with the sides (I had already been considering this or some other treatment to better color match the sides).

Brad


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We thin to joining thickness than bake - the color change runs all the way.

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Thanks, makes sense. Appreciate the tip!


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I recently bent 2 pairs of Cocobolo for current guitars - 1 very figured, the other not quite as much. I thinned to .078 or so, and didn't do anything different with the exception of wrap in paper, and used my bender. Bent easily. The only thing i noticed was they scorched a bit (not a problem, sanded out), and was a bit surprised cause i didn't use a lot of heat.

Glenn

Most rosewoods bend like butter. Cocobolo is not a big deal. Follow Woodie's suggestion on paper to contain the resin mess, and lower peak heat with a longer warm cycle.

Andy

What do you mean by figured?

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