Super Soft II for Khaya sides?

[charles Tauber]

From your description, it sounds like you aren't wetting the wood sufficiently.

While it is heat that plasticizes the wood and allows it to bend, steam is an effective vehicle for distributing that heat. In general, wood is steam-bent. Guitar makers usually try to limit the amount of steam/moisture since, on very thin woods, it can cause the wood to "potato-chip" or ripple across the width of the piece.

Given the issues you are describing, I'd suggest you start by erring on the too-wet side - if there is such a thing. Once you have success with that, you can reduce the amount of moisture you use in your bending process.

In the "old days" - like the 60's and 70's - many makers actually boiled their sides in a trough prior to bending. Some bent the boiled/steamed wood over an unheated form, which is pretty typical in other forms of bent woodworking. The traditional method of bending instrument sides has been dampened wood over a hot pipe, a method well worth learning if you have the inclination. (Those good at it can bend a pair of sides over a pipe in 20 minutes.)

Charles Fox invented the light-bulb-heated side bender - now almost universally using a heat blanket instead of light bulbs - in the mid 1970's. Even then, it was used with well-wetted sides prior to putting them in the bender. The bender should be sufficiently hot - heated with light bulbs or heat blanket - to hear the water sizzle as it contacts the hot metal slats.

Once the wood is in the bender, it takes a fair amount of force to bend the waist and to use the "sliders" on each bout. In four decades of bending sides in a Fox bender - until recently still heated with light bulbs - I've never had a piece of wood that won't bend or break. My suspicion is that you are expecting the wood to bend far more easily - i.e. with a lot less force - than it requires in the bender. Hence my having difficulty understand when you say "it won't bend". In my experience, it either bends or breaks, very rarely breaking, particularly at the thicknesses you are describing.

As an aside, in my Fox bender, on top of the form insert, I currently use a sandwich of a metal slat, the heat blanket, a metal slat, the wood to bend, another slat. I place the temperature probe between the second metal slat and the wood near the waist. I don't currently wrap the wood in foil or paper, though I have used both at various times. I spray the wood well with tap water, to the point of dripping, with a hand-held plant sprayer. In my setup, the wood begins to smoke at about 200 F, suggesting that it doesn't read temperature accurately since I know by the sizzling of water/steam that it is hotter than that. I could calibrate it but I don't really care the actual/accurate temperature, as it is just a reference: I know how hot it needs to be to bend correctly, based on feel and sound.

[redir]

I used to soak the sides in a bath tub full of water with bricks to hold it submerged for an hour before bending. I never had a problem doing that except that realizing later that it's just not necessary to get it that wet. But as Charles suggested erring on the side of too wet is probably a good idea. You also need a thermometer to know how hot you are too. You should be at 250deg F or higher when you start to bend the lower and upper bout.

If you have never bent wood on a hot pipe that might also be a good lesson. Once you get a feel for what it takes to bend a side set it makes more sense when using the bending machine.

[printer2]

I use SSII and it helps from what I have seen. I use a paint brush to brush it on the surface and wrap it in plastic wrap overnight. I then wipe the surface with a damp rag. I then bend on a pipe with a damp rag draped over the pipe. So the wood temperature does not get over 212 F.

I used to bend on a form with a heat blanket and have noticed some sides not wanting to bend even as I turned up the temperature. This is conjecture but I think the wood stopped wanting to bend after all the water had been boiled away, no more steam coming from the bender.

I learned a little on torrifying wood and in the process a little on bending it. Water lowers the torification temperature a little (ok steam at those temperatures) and I have the idea that moisture in wood helps a piece to bend. Think it had to do with graphs on the elasticity of wood with different moisture levels. A fresh cut tree will let you bend a piece of it easily.

The SSII seems to do the same thing to the binder in the wood (brain does not want to spit out the word, I don't feel like searching) as ammonia, I am guessing the Zep might have some in it. The water in the Zep also wouldn't hurt. When using the SSII, unless you leave the side in the form for a length of time the SSII in the wood will allow it to spring back. I am guessing people who bend in a bender balance the amount of water used with the temperature bent at. If the piece is dried out before the wood becomes plastic the higher temperatures do not help in the bending.

I know, all over the place. It would be good if I kept or could remember all the bits of information I pick up and why I think how they relate to each other, I probably would have gone somewhere in life. No biggie, the point is different people have different recipes on how to bend the same piece of wood. And it may have to do with the different amounts of heat and water present, you keen a 3D map to get all the relationships in there.

At least I think.

[kmanuele]

Charles;

Agree, and I suspect the wood itself is too dry in my shop environment.

They bend quite easily in the bender. They just would not retain the bend (too much spring-back) when taken out of the bender, and enough inherent stiffness that I was reluctant to force them into shape in the mold.
Re: slat stack. The same, except I put the wood on top of the blanket, so any scorching happens on the inside.

[kmanuele]

Speculating:

From what I can tell, Windex (ZEP) is mostly water with some ammonia and other cleaning agents. As a glass cleaner, it evaporates quickly. Probably not so with SSII? So when I let the ZEP sit for an hour on the wood, it just evaporated and there was none left going into the bender. Wetting with ZEP and wrapping with foil retained the moisture and ammonia.
Still not sure if success was due to ammonia, or just the water retained by the foil.

[John R]

Never any problems with all the usual woods even .100" eir in slope shoulder was easy in fox machine. As a beginner I used boiled water only in a tray on stovetop and clamps/cauls before making a fox bender, never any problems. Ash Maple and Black Walnut Cherry, so all pretty easy.

With those good experiences I felt ready for 'better' woods, I resawed khaya once after reading about some of its idiosyncrasies. I tried everything your mentioning except the treatment. at .080" Tension breaks at the waist clear through, bubbling when I tried water soaking etc etc. I gave up after a few sides. But I was using no backer, or fox bender.

I think it is just 50/50 with the source wood you get, and khaya is just not great for this at all IMO. Sapele. Utile, Genuine, all much better from what I have read on forums about this issue. Maybe resolve to laminate instead

One thing I noticed on the guild forum and, maybe some Martin pics, showing some of the old equipment from Westerly days was the cast aluminum forming press with heat coils. These can also have water cooling for the down cycle. I guess it heats very fast and presses very fast and the wood has nowhere to go but into the shape. The backing stiffness of the castings is a factor I imagine. So speed and heat and backer and luck getting good wood may be the issues.