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Hi guys,

humble question, , What should be the best temperature to bend Black limba sides ?
Is it necessary to wrap the sides in paper ?

thanxs in advance,

frans

_________________
Don't worry be happy.

I use 350 with wet paper .

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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

With Black limba you may want to keet it right at 300 to keep it from scorching.
I have built 3 guitars from it and it's a pretty easy wood to bend and work with.

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Peter M.
Cornerstone Guitars
http://www.cornerstoneukes.com

Thanxs alot,

I try the 300 dgrs and shall wrap it in slightly wet paper.

I bent the koa on 278 and it bend easy at a thickness of .80 ( 00-size ),
which thickness do you advise on the limba for an OM based size.

frans

_________________
Don't worry be happy.

Hi Chris,

That's a nice BL back; did you finish this one already ?
I like the body shape but was wondering how you did/do the armrest to match the curve of the top aesthetically speaking.

frans

_________________
Don't worry be happy.

Black limba can be brackish and do some serious cracking. The first Black Limba I bent , went like butter . The next planks had a horrid time bending. You have no fear of scorching if you keep the wood wet . Once you are on the pattern you can back off the temp and use a dry out cycle .
Also too much water can cause warpage so the key is to bring in enough water to get the job done without over soaking it . A touch of downy fabric softener won't hurt .

_________________
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, thank you for responding with more info.

what would be in your opinion an appropriated thickness for an OM-size ?

frans

_________________
Don't worry be happy.

Our goal in blanket bending is not to simply heat the wood to some selected temperature, but instead to take a controlled, evenly distributed amount of water and convert that to steam as we accomplish the bend. Indeed, until the water has been turned to steam, the temperature of the wood will not rise much above the boiling point, as all of the excess energy being generated by the blanket is taken up in the phase change from liquid water to steam (i.e., it takes about 539 times as much energy to move from water to steam as it does to raise the same amount of water just one degree F, so we see a pause during bending as all that water is flashed to steam).

- Control the amount of water by wetting the paper in the bending package instead of the wood itself. Not only does this evenly distribute the water, but it also allows the amount of moisture to be controlled based on the relative sheen of the paper... satin is about right for mahoganies and anigre, while other woods that prefer more water or luthiers that need a bit more time to get the bends done and set, a glossy or semi-gloss appearance to the paper gets that done. Another good reason to use butcher paper (FWIW, brown is much more absorbent than white, but best to use white with very light colored woods like holly) is that for resinous wood, the butcher paper drinks up all that hot resin and avoids depositing it on the slats (to be removed with relatively harsh solvents.

- Bending temperature is much lower than peak temperature. We begin bending as soon as there is evidence of steam being generated in the bending package, and once the bend is complete and the water in the package has been exhausted, peak temperature begins the process of pushing trapped water out of the wood as well as acts to lock in the bend for timbers which are relatively resin-poor like limba. Because the free water in the bending package has already been expended as steam by the time peak temp is reached, all bending must have been accomplished well prior to that highest temp point in the cycle. In general, a short pause – perhaps a minute or so - with blanket on full after any sign of steam generation has disappeared will get the stack to about 280-300 degrees F, and 2-3 minutes after steam ends will get closer to 320-330 F. At that time, the blanket can be set at perhaps 80% on a router control (variable versus full, and at the bottom of the red arc or just below) and the package allowed to dump any further trapped moisture for 20 or so minutes.

- Using cut-to size foil and paper sheets (e.g., 6" x 35" slat size) takes about as much time as making up an 'envelope' and increases the area through which water vapor may be pushed out of the bending package. This avoids the primary issue with envelopes - trapped moisture re-condensing as the stack cools and re-wetting the wood. A secondary issue with closed envelopes or a sealed edges (i.e., paper and/or foil folded over the edge of the wood) is wrinkling or rucking of the paper and foil, leading to additional marking and the need to scrap or sand off those markings. We want the bent side to come out of the bender uniformly dry and with little to no spring-back, so paying attention to where we are in the bending cycle is worthwhile.

- I've mentioned before that most of the student failures I saw were the result of waiting too long to start the bend, with a consequence of running out of available moisture to flash to steam before completion of the bend (complete = final hard-setting of the waist). With black limba being a fairly easy wood to bend in a Fox-style bender, the fix is to 1) make sure adequate water is available, 2) use a 5 watt/square inch bending blanket running at full wattage to quickly generate steam, and begin the bend as soon as evidence of steam generation is seen.

I just finished a set of sides at Greenridge this past week. The material was sinker mahogany somewhat compromised with numerous across-the-grain worm holes. While Super Soft was used, the real edge in bending was just getting things done as soon as the steam started rolling off the side. As mentioned, there may be timbers that really do need some sort of exotic time-versus-temp ramp to bend well, but simply getting the bend going at the right time and moving through the process with dispatch seems to give near perfect results without additional items in the bending kit.

Piling on here………Has anyone had success with bending and having no spring back with a Fox style bender. I haven’t thus use a hot pipe.

Woodie thanks for the detailed description of your technique. I hadn't thought of leaving the aluminium wrap open. Next time.

Cheers Dave M

Just to clarify, not a technique I developed - just what the shop was already doing when I came in the door. As to springback-free bends in the Fox, most of the issues I saw with student guitars had to do with too much time spent assuming the bending package needed more time to heat beyond the point where steam was coming off the stack, failure to hit peak temp and then allow the wood to thoroughly dry and set (avoid closed foil or paper envelopes), or failure to get enough water in the package. Likely 90% of under-bent sides I saw were the result of waiting too long to begin the bend and exhausting the available water before the waist or cutaway was hard-set.

Also worth using Supersoft on woods that are figured or tend to suffer fiber collapse when bent too wet (another reason to put the water in the paper rather than soak the wood surface).

Other tips:

- Rosewoods are often ready to come out of the bender while still warm, versus mahogany or anigre that really wants 12 to 16 hours in the bender.

- If you do find your side comes out of the bender a bit damp in the waist, load it back in sans slats, etc. and reset the bouts, cutaway, and the waist, then allow to dry for another 12 hours. Sometimes an under-bend is just too much water left in the side, so a little strong persuasion and time's healing balm (and evaporation) can help, and certainly should be tried before taking out the pipe for touch-ups.