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I wanted to build my first Venetian cutaway but didn't have the molds or bending machine mods to use my bender so I built a quick bending iron using a BBQ starter. The wood in question is a striped Sapele and try as I might I could NOT get this wood to bend. Water, no water, hot, hotter, hottest - it would bend only so far then break. Tried a LOT of different techniques and even though it's been a while since I've bent sides I have had success in the past, but this wood just seemed extra stubborn.

I figured it was my technique so I built the forms and mods for my bending machine and thinned to around .075 and gave it a go. The waist bent fine as it had for a couple previous builds but the cutaway broke in the same way it had when bending by hand.

Used water on paper (some have said not to use water?) and bent around 300 - 325 degrees. Seemed to go OK but the bend (break) came out like the pic below.

So I thought maybe it was just the wood. I had some ambrosia maple laying around and thinned to the same .075 lots of water (no idea if this is good or bad) but it bent down right easily. Perfect bends with almost no spring back.

So I don't know if it was just a stubborn piece of Sapele? Bad technique? Either way I won't try again with that Sapale after so many failures but am curious do the pics tell you anything? Run out? Just stubborn and time to move on?

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Larry,

Looks like you're fighting quite a bit of runout to me.

M

Some pieces just won't cooperate...

That looks like a pretty tight bend so that makes it more challenging. If I'm not mistaken, the figuring in that sapele is caused by the grain running in and out of the surface. That makes it more prone to separating on the outside surface of a tight bend especially if wet. I haven't bent sapele but I've found that the tendency for woods like that (curly koa, highly figure bubinga) to separate on the outside of a bend when bending on a hot pipe can be reduced by applying water only to the inside surface of the bend.

For figured woods in particular, I treat the sides with SuperSoft veneer softener before bending on the hot pipe. That makes them a lot more cooperative.

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I've always had problems bending sapele. Too bad; some of it looks great.

Sapele is just hard to bend. I’ve had it break bending the waist of a dread (hardly any bend at all). The figure curls through it such that wherever you are bending, there is runout. I prefer to build Venetian cutaways, but when the side breaks at the bend, that guitar becomes a Florentine.

I looked back through my notes for the guitar below I built some years ago that has similar figuring. The seller called the wood "African Mahogany" but it might be sapele. The sides set for that guitar bent fine so it might be that the particular piece of wood you have was the problem.

In case it helps, the sides were 0.080" thick and my hot pipe was set right around 400 degrees (maybe a higher temperature would have helped for your sides?). I spritzed the sides with water while bending. This was done before I started using SuperSoft.

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Balsamo wood is very hard to bend an so is zebrawood for me using a watlow heating blanket . They bend very slowly and are prone to cracking at the tight bends on ukes

I've made 2 Sapele guitars & it was a PITA both times - each time I cracked sides.

Kevin Looker

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In the beginning I had issues with 5 sets of Sapele. it boiled down down to not being thin enough, not the correct heat combo and/or bending to quickly.

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My first thought was that it's not enough heat but then I've never used Sapele before and from the comments apparently it's a difficult wood to bend. But I'd go thinner for the cutout area and up the heat. A drop of water should jump, pop and sizzle off the iron before you bend on it.

Thanks so much for all the comments and replies.

I'm not that experienced in bending wood but tried as hot as I dare, even a little scorch, and the wood from this re-saw just never gave up.

After the experience with the maple that bent like butter, I'll bend any remaining Sapele without a cutaway as it bent through the waist a couple of different builds.

Again thanks for the comments and information.

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If you want to save the cutaway side, make the cutaway in two parts and join with a solid block. I took this idea from my Grandpas' Selmer Maccaferri - the cutaway had been put in after the guitar was made.

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nigel

http://www.theluthierblog.com

Larry, I've had Bubinga act like you're describing and, in fact, the first set of Bubinga sides I bent (I use a pipe) were too scorched to use. For the next set I did the same thing but put a piece of cloth on the iron and kept it dampened with a spray bottle while I bent the sides at high heat. That worked. For cutaways and/or hard to bend wood I also like to to use SuperSoft 2 https://www.veneersupplies.com/products/Super-Soft-2-Veneer-Softener-Conditioner.html.

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Steve Smith
"Music is what feelings sound like"

When I have had wood that would not bend I used a supersoft, a steam box then the blanket and form. I call it the triple play. So far it hasn't failed me. But then again I don't use saple.

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Michael F Smith
Goat Rock Ukulele
http://goatrockukulele.com

What sort of support is the bend getting in the cutaway area, are you using a bending aid (SuperSoft II), and are you getting the bend started in sufficient time to finish the shaping while there is still adequate moisture to generate steam to plasticize the wood?

Based on what I've seen here over the past three years, the tighter the bend, the more critical the need for the slats in a blanket-type side bender to fully support both inside (failure in compression or buckling) and outside (failure in tension) of the bend. Although just about any thin metal will work for slats in the moderate bends seen in a full body guitar, we move to string stainless or - better yet - spring steel when bending something tighter than 1.5" radius on our Fox-style blanket benders. Spring stainless provides more support than standard stainless, and spring steel is heads and shoulders above spring stainless when it comes to resistance to bending and thus, support in the bend for both surfaces.

Sapele (Entandrophragma cylindricum), Khaya (aka the African mahoganies), the genuine mahoganies (Swietenias), and the acacias (A. koa, A. melanoxylon) all seem to want a very quick rise to bending temp, just enough water to get through the bending cycle, but not enough to fully saturate the fibers under compression on the inside of the bend (thus causing local buckling failure), and benefit from pre-treatment with SuperSoft 2.

Our usual process for bending calls for a rapid rise in temp, with bending started as soon as visible steam is generated in the stack (waist, then lower bout, then upper bout or cutaway), so we always use a 5 watt/square inch blanket (ours are all proTherm models from Mr. Hall). Worth making sure your blanket is not the 2.5 watt/square inch or even lower model which will burn through the moisture reservoir before getting to bending temp, and that whatever timer/rheostat control you are using allows 'full open' current to the blanket for the first 8-10 minutes of the cycle.

A sure sign of a slow temperature rise and related exhaustion of the moisture in the bending stack is a side which will not hold shape and has excessive spring-back after bending. If your sides have minimal spring-back, it would seem that the issue is more likely either lack of support in the area of the bend or a need for pre-treatment of a wood that benefits from that prep.

Use of a steam box seems to me to be counterproductive here, as the issue is not getting penetration of heat and additional moisture into the center of the wood as with thicker stock, but instead a quick rise in temperature and a flash of steam generated by a relatively small amount of water - just enough to last through the bend and not so much as to encourage the sort of fiber collapse we see in over-damp woods of the species mentioned. Perhaps a very short steaming cycle would avoid picking up too much moisture, but the available window of time to get a side from steam box to bender and worked before the surface temperature dropped below the boiling point would seem to be quite narrow, given the very small volume of a typical side, relatively meager mass, and large radiating surface area.

Finally - it could be worse...you could be trying to mill and bend anigre!

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Great post! I also switch to stainless on a cutaway but I offer one caution, the spring steel can have enough spring to crack the side when getting it out of the bender. I use some clips to hold the inside slat in the venetian cutaway before loosening the cutaway clamp.

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Yes some wood most certainly doesn't want to bend! It took me a while to decide that this home dried sycamore just wasn't going to behave. Dave

Anyone with experience with Goncalo Alves?

I've got to bend some Brazilian Tigerwood / Goncalo Alves for a Florentine cutaway, but with a more modern OM with tighter radii on the upper bout. Initial tests with scraps shows this one is a little more tricky to bend.

SuperSoft veneer softener - is this stuff the same or is SS2 THE stuff to use? https://www.woodcraft.com/products/veneer-softener-tamer-pint

Great advice Woodie and will heed it for future bends.

Thanks

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The sides look a little thick, how thick are they? If you try it again I'd probably thin them down a little more.

One of the major reasons I moved to laminated sides was that it made bending so much less stressful because just about anything bends easily at 0.050", even stubborn curly ebonies like Malaysian Blackwood bend with ease. I broke a really nice side of Malaysian Ebony at the upper bout while bending (turned it into a Florentine cutaway) that prompted me to move to thinning and then laminating the sides. It took some work but I haven't looked back since. If I were building Venetian cutaways (I don't) I would definitely want to bend very thin sides then laminate.

I screwed the spring steel right to the bending mold to avoid that exact problem after I felt like I was about to snap a side. If the mold is wide enough the screws won't be in the way. If the mold is more narrow you have to take care to get the screw flush and then grind perfectly flat so as not to mar the wood.

The next time we bend cutaways, I'll have capture some video...there is a step-by-step procedure that the boss teaches that minimizes the chance of the slats popping a side or set of bindings...IIRC, the lower bout and waist are relaxed, the blanket slatand upper slat pulled through, and the now-freed blanket and upper slats clamped so that they cannot exert much in the way of a load as the cutaway ram is released, leaving just the inside slat to fight.

Keep in mind that the purpose of the slat is to move with the wood to provide a tension strap effect on the outside curves, and anti-buckling support on the inside curves...fixing the slat to the mold seems like it would take the slats largely out of play in that role.

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Some great advice here and many thanks. Love the idea of laminating but need to invest in a set up of sorts, perhaps down the road a bit?

In the case in the OP the Sapele was thinned to approx. .075 and was successful bending more than one side (waist) for a non-cutaway couple of guitars, it was the Florentine curve that would not behave. Nor would it behave thinner with all kinds of heat and moisture combinations on a hot pipe.

I thinned some Maple as stated in the OP to the same .075 and it bent like butter. Not saying there might not be a method to bend that particular Sapele but I will not attempt again and have decided to simply use the remainder for non-cutaway guitars.

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Curious about the lam system you use? I've seen strictly molds and a vacuum system using existing molds.

https://www.youtube.com/watch?v=n_iKG9hyggk

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