Official Luthiers Forum!

Ok so its been about 6 months since my last build and I got the itch to start on a new guitar. Im doing koa sides and a sitca spruce top. The koa I bought hasn't shown up yet but it looks lightly figured. I have struggled in the past and need some advise.hot pipe is not an option for me I hate it and am terrible at it. I invested in a digital heat blanket and made my own bending machine. But I have had two issues. The first time I broke one of my sides. I was bending Australian Blackwood. I used 2 metal slates and got the craft paper wet. Followed everybody's instructions on bending. Started bending When the blanket got to around 275 if I remember right and when I got to the upper bout it cracked. I Didn't have a thermometer in between the sandwich. I was just going by the digital one that controls the temp of the blanket so does anyone know if that would be why I'm having troubles. Maybe Im bending before the heat transfers into the wood. It was steaming so I thought it should be good to bend. The second time I bent on the machine I bought new sides and superset 2. I sprayed the sides generously and covered them in wax paper overnight. The next day I did not let them dry. They were still damp with supersoft and I wetted the paper and they bent but I had stains so bad On the inside and outside. I got them sanded out but not on the inside. They were so bad I gave up. I didn't use distilled water like I should have or maybe I should have them them dry first from the supersoft. I don't know but does anyone have some answers for me. I want to buy a steamer and make a steam box for my koa sides. Maybe that will work better for me. If I do steam them should I still use a heat blanked or just take them out of the box and press them onto the mold without a heat blanket and metal slats. Or maybe i don't need a steam box and just need to get a thermometer inbetween by slats and wood. Any answers for me would be greatly appreciated.

My recommendation: buy several sets of junk sides from LMI and practice. We can all guess at what went wrong, but we will just be guessing. You have to make mistakes, experience them, and figure it out. Then you can do a better job on the good wood.

A few things to watch out for:

Thin the wood to 0.085" at the thickest.
Get the wood itself wet, not just the paper. Not soaked, but directly wet.
Make absolutely sure the blanket is touching the wood where you want bending to occur.

Good luck with the practice sides!

+1 on practice sides. I did four of those before doing the first "real" ones. The practice sides that LMI sent me were curly maple. Now that made for some good practice on my hot pipe.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Get yourself a digital meat thermometer, use it in your sandwich. You need to know the temperature of the wood, not the blanket.
Cal

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Remember, there are no stupid questions, only stupid answers!

The cracking may have resulted from the side getting to hot and drying out. The staining may have been from a reaction with the metal slats or from scorching, or both.

In your sandwich you may want to use wet craft paper next to the wood, then aluminum foil then heating blanket then metal slats.

Starting your bend at 275 could very well have been to hot causing the side to dry and become brittle. I use a thermal coupler but also keep a close out for steam. I start the bend at the waist when steam starts and you hear some sizzle, around 225. With your set up you are probably heating to high. Also, you will want to smell the steam to be sure it isn't smoke. If smoking starts spray water into the sandwich to cool and turn the blanket down or off.

Mahogany is good practice for bending koa. they are similar

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Joe Beaver
Maker of Sawdust

There is a series of three videos on YouTube that cover a technique for bending figured mahogany that should work well for koa and other acacias such as Tasmanian blackwood. You can find the first one here: http://tinyurl.com/hgjlga4.

If you can manage to obtain a gallon of veneer softener such as SuperSoft 2 (best price is direct from VeneerSupplies.com), the benefits associated with use for figured woods such as curly maple, mahogany, and koa can be significant in terms of reducing the risk associated with bending these woods. We use it as a matter of standard practice on anything figured, any hard-bending woods, and on flat or rift-sawn stock such as birds-eye maple.

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A constellation only takes shape when one maps the whole.
- Beth Brower

OK
1 if you use SS2 you spray it on and let dry.
2 how think? .070 is plenty thick
3 don't put a thermomter in the stack unless you want a crevice in your wood. The wood gets soft you can put a sink in it
4 yes you want it hot but there is a knack to get the feel
5 practice and don't over soak your wood. Too much water can be bad as too little.
6 the key is to work the heat into the wood and feel the wood relax.

SS 2 will color the wood but will sand out. If you have blues steel slats you can expect staining. I used stainless .

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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

Thanks for all the replys. For the stains in my wood it shouldn't be from the metal slats because I had them wrapped in craft paper and I thing I wrapped them in aluminum foil too. I work at a cabinet shop should I just practice bending somenscrap maple..and see if lmi has some mahogany

I have ruined sides using the common brown/tan Kraft paper -- the dye in the paper leached out and caused indelible stains in a nice set of curly cherry. I recommend the white Kraft paper, we actually use parchment paper found in the grocery store baking aisle.

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Ken Cierp

http://www.kennethmichaelguitars.com/

In terms of your process. You must rely on the wood - not the numbers - to tell you what to do.

Put an oven mitt on your hand and feel the wood package. Press down on the package to feel it as it bends.... When the temperature is about right - you will feel the wood relax and soften under your hand pressure. Get to it right then and bend away. If you go too slow - it can stiffen back up.

If it's not getting flexible but it's really hot - stop. Maybe try wetting down the sides more. I bend mostly straight wood - but I find more water works better than less. ESPECIALLY with Mahogany.

Practice wise. Straight grain American hardwood (such as oak, ash, maple, cherry, walnut, hickory, poplar, aspen, birch, box, and sweet gum) makes great practice wood. Doesn't matter if it's flat or quartersawn for practice duty. Just stay away from stuff with knots in it.

Equipment wise... early on, I had the adjustable controller and the temperature sensing. I ended up burning it up by mistake - and had to just plug the blanket straight into the outlet... Bending got about 500x easier to do... I now just make up the package, plug it in and run it full 100% wide open. I start bending as soon as the wood starts relaxing... Bending takes me 25% the time as before when I had all the fancy stuff trying to more carefully "regulate" the process. And I just unplug it when I am done.

Paper wise - I just use white non-dyed paper towels. I just unroll 4' or so, wet them down, squeeze out most of the water, and off I go. You just have to use quality paper towels that don't turn to mush when they get wet. Call me a phillistine.

Thanks

We've never seen other than the usual grain raising and minor, quickly sanded off staining. We always use a barrier sheet (foil) and either the brown or (when bending holly) white butcher paper. We avoid wetting the wood at all while stacking the bending package, using the paper to hold the exact amount needed, which eliminates the staining associated with all that liquid, mineral-laden water.

As someone that loves baking and is very aware that whatever goes into the oven ends up in the cake or pie or cookies that come out, I avoid grocery store parchment paper such as Reynolds in favor of the mail-order silicone-free variety. If using parchment paper for anything other than baking, make sure it states that it was not treated with silicone; otherwise, expect the heat and vapor pressure generated by bending to move the silicone from parchment paper to anything in contact with the wood, or the wood itself. Even 100% unbleached, 'good for the earth/If You Care' branded paper simply guarantees abundant silicone is present, as the environmentally questionable component is not the silicone, but rather the heavy metal-laced quilon treatment on some non-silicone parchment.

Although we have in the past used flat-probe thermocouples to monitor temperature, we've gone to simply starting the waist down as soon as the first whisps of steam are seen. We bring the waist down to about 3/8" off the form, then bend the lower, then upper bout...all this takes perhaps two minutes to do, and is completed before the water present is converted to vapor. The bending issues I have had have all been related to waiting too long to start the bend on woods where we are carefully controlling the water.

Excessive spring-back and failure to take a bend seems to be a problem that always relates to expending most of the available water in the package before starting the bend, so going with 'first whisps of steam' as the starting gun works for us.

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A constellation only takes shape when one maps the whole.
- Beth Brower

FWIW, I like heavyweight plain wallpaper lining paper, no water on the wood.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Here is my take on side bending. Non figured or lightly figured koa is easy to bend. Should not give you any trouble. My article shows uke sides being bent. Guitar sides are easier. My thickness for guitars is about 2.2mm. Enjoy your building! http://www.pegasusguitars.com/how-i-ben ... sides.html

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“ The meaning of life is to find your gift and the purpose of life is to give it away” Pablo Picasso

I really like that hinged waist caul tower! Brilliant -- Ten gold stars out of ten.

Thank you, I just may copy that design.

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Ken Cierp

http://www.kennethmichaelguitars.com/

I generally follow the lower temperature recommendations above- I start bending the waist at about 225 F, and try to finish before all the steam is gone, usually around 275-280 F. I do the waist to 3/8" above the mold, then the lower bout, then the upper bout. About 1-1 1/2 minutes for everything. I do use a flat temperature probe in the sandwich. I want to know the temperature the wood is at. When bending heavily figured woods- I've recently done Koa, Maple, and Primavera, I use Supersoft II that I let dry overnight. I spray the wood and let any excess fall off. Then wrap the wood in wet butcher paper- I used the brown kind, even for the Primavera (luckily no staining), then wrap it all in aluminum foil- I believe the aluminum foil is a big help by containing the steam in the package longer. Bending stack is SS slat, blanket, wood package, blanket, SS slat, held together with spring clamps on the ends. I built a solid state controller that helps me control the temperature- I set it to 270 F for the bending, then up to 310 F for 10 minutes, then back to room temp. If I have the time, I let it sit overnight, but if I want to get both sides done in one go, I take the wood out of the bender and clamp it in my external mold overnight.

I'm on well water with iron in it, but I have multiple treatments- ozone, greensand, softener, followed by a Reverse Osmosis filter. That's what I use for the bending- works fine so far.

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Gene

Politicians and diapers must be changed often, and for the same reason- Mark Twain

I will remind once again --- Even with their High Tech side benders, Martin thins the blanks to .078"

It is my belief that trying to bend material that is too thick is the number one self inflicted bending problem.

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Ken Cierp

http://www.kennethmichaelguitars.com/

It certainly is true that thinner wood bends easier.... And I think the #1 thing you can do if you are having problems with some specific wood bending is to go thinner. I had some evil Sapele once upon a time that just would not bend at any reasonable thickness. I ended up with sides at 0.065" thick and I decided Torres would be proud

I will say that certain easy-to-bend woods will bend just fine far thicker.... The last quartersawn oak sides I did bent at 0.145" thick. Quartersawn Cherry (probably actually heartwood maple) at 0.140".... I used this thickness because I am shooting for heavy sides and the attendent benefits of such. Both bent without any issue at all. The oak actually flopped onto the form once it got hot... Oak is the only wood I have ever had over-bend (instead of the usual springback) using heating blankets and bending forms.

Thanks

The foil between the wood and the slats with stop the metal staining. Just paper will not.

And yes, practice makes perfect. I think in general, when it comes to bending, there are two types of woods. The oily and the not so oily. In the first group there are are the rosewoods and ebonies, and some of the tropicals, and in the second, most of the rest.

And of course there are two sub categories for each, figured and non figured. In general oily woods bend easier. Non oily wood might take a little more heat and water and figured wood tends to cup with to much water.

My point is that the procedure that works well for a certain category might need some tweaking for another. If you can practice with each before you bend the real deal you are indeed a fortunate fellow. Seems to me technique is about 60% of it, with side thickness, moisture content and heat about the other 40.

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Joe Beaver
Maker of Sawdust

I made 8 practice sets after work today. Maple and 5 sets at .70, 2 sets at .85 and 1 at .75. I just bent the .70 and it was really easy. And I bent the .85 and that definitely took more to bend. I got the wood wet and the paper towel damp. Wrapped the wood with the paper towel and then wrapped that in foil. My sandwich from bottom to top went slat wood heat blanket and then slat. I ignored bending at a certain temperature and instead started when the wood started to drop on its own and I could see steam. It didn't really start sizzling till I was done. So I ended up bending around 225 with both and with the .70 I was done bending around 260degree and the thicker .85 I was done around 290degree. Everything wend good but I did have some minor stains only on the inside. I used tap water so maybe that's why? Is .70 a good number for thickness on most types of wood to make it easy? Also how long should I let the wood cook for after im done bending and at what temp

A lot of good advice has been shared, and I think you'll find common patterns even if the exact details aren't always the same.

I use Todd's method, which is what Woodie linked to and described. My current guitar is highly figured koa. I sprayed with SuperSoft II the night before, let it dry as John Hall mentioned, and bent according to Todd's method, wetting the paper with water straight out of the hose. The bend came out great.

Stick with it. You'll get it!


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