MIMF

Hey folks, I have checked out this site a few times and I have to say that all the additional information here tied with books of reading has really helped in my quest to become a luthier. With that said, I thank all of you, and say hello!
I have run into some big trouble with side bending. 6 pieces of wood, all snapped. Wood bending is all new to me. I saw that steaming is relatively ineffective because of the width of sawn wood used. So I decided to go down the route of heating an aluminum tube with a blow torch. After finishing the first bow of the bottom of my soon to be OM, the board simply cracked. I may be using the wrong type of wood, or have a bad technique?
To note: I did not do this hastily, or without caution. My wood was soaked overnight, and spritzed with water accordingly. Maybe its time to switch to a 200w lightbulb and dial it down? My technique required heating of the tube for about 15 seconds every minute of the bend. Should I have left the open flame shooting inside the tube the whole time?
I am lost, and any help provided is very appreciated!

Hi Caleb,
Yes, you should probably left the flame on the whole time. Aluminum doesn't hold heat as well as steel or cast iron.You want the pipe hot enough to where drops of water dripped on the pipe sizzle off the surface.
What type of wood are you bending, and is it quartersawn or flatsawn?

Don't soak overnight. Just a light spritz before bending. Also, how thick is your sides? They should be no more than about 0.080".

Go slowly. Get the pipe hot enough for a drop of water to not only sizzle, but bounce around on the surface of the pipe and keep it that hot. Gradually rock and move the side over the hot pipe to heat it. You will feel the wood relax when it is ready to bend. Do not force it. PRACTICE ON SCRAP!!

Caleb,
The pipe needs to be hot the whole time you are using it, so yes, keep the flame going. dial it down to "low heat" after it is hot enough (dancing drops) and you should be able to keep it pretty much the ideal temperature. I use a galvanized steel pipe, which has more thermal mass than aluminum, so the temperature doesn't swing so much as the heat transfers to the wood. Adjusting the flame should take care of it though. If the wood discolors you need to move faster, wet more often, turn down the heat or some combination of the three.

There has been raging debate over how long / if to soak the wood. There are pros and cons to each side, but it really depends on the wood as to what will be effective for your technique. I've always started soaking both sides right when I light the torch. By the time the pipe is hot enough to use the first side is ready to bend. It takes me around 10 minutes per side, so the second side soaks for around 13 minutes. The second side always bends easier than the first. If the wood gets too hot/dry you can get a case hardening effect where it won't bend (in that area) any more no matter what you do. This can happen if you "worry" the wood in a particular location too long. Depending on the wood (again, sorry, experience is required) it's possible to get the wood "pretty close" and clamp it tightly to the form overnight. This often will allow the wood to set in the proper shape, assuming you were close enough and the wood was still somewhat wet. Similarly, bending wood binding (& purfling) can be done "pretty close" and taped into the slots to form a good fit.

I don't know if you have done this already or not, but it helps to stuff the end of the pipe with steel wool so you don't burn holes in your shirts and it helps keep the temperature up in the pipe. One thing I did wrong when I started was orienting the torch so the flame shot directly on the top/bending surface of the pipe. It got too hot, too quick and scorched wood. I reoriented the flame toward the bottom of the pipe and this, in concert with the plugged end, seems to work well. Another good tip is keeping a clean, white, cotton rag (a t-shirt or dish towel) in a bowl of water. When you go to bend, wring the rag out and place it on the pipe, then place your wood over the top of the rag. The steam from the rag helps and it prevents the wood from getting scorch marks. Just make sure the rag stays damp or it will burn.

Excellent point. I have always used a cap on the end of my pipes and it didn't occur to me that anyone wouldn't. I also drill a number of holes in the bottom of the pipe so there is some (hot) air flow through the pipe that isn't directed at body parts. I seldom put the "nose" of the torch further than about 1/4" into the pipe itself, but the flame is completely in the pipe. I also make sure the flame is horizontal (parallel to the pipe). The cap is important because it allows a more even heat on the pipe (via contact with the exhaust, not direct flame) and I can stand directly in front of it when bending for leverage.

Justin Bretz wrote:I don't know if you have done this already or not, but it helps to stuff the end of the pipe with steel wool so you don't burn holes in your shirts and it helps keep the temperature up in the pipe. One thing I did wrong when I started was orienting the torch so the flame shot directly on the top/bending surface of the pipe. It got too hot, too quick and scorched wood. I reoriented the flame toward the bottom of the pipe and this, in concert with the plugged end, seems to work well. ...

I bend most woods totally dry, with little problem. I do put a wet paper towel on the pipe when I'm bending the waist to cut down on scorching. Mostly it's a matter of waiting long enough for the wood to get hot enough to become elastic. You can feel it when it starts to give. If you just keep light pressure, you'll feel it start bending without much force. Every wood is different though, so you have to feel for it at different temps.

A word of warning about open hot flame as from a propane torch, and steel wool, it can ignite. Put a cap on the end of the pipe.

Thank you all so much for your help! I did not have a stop placed at the end of the pipe, for fear of thermal expansion. Steel wool or a cap will definitely be added on my next attempt. I will try using galvanized steel this time, because I was getting scorch marks in some areas, and none in others. That must have been due to the incongruity of heat...
Also adding a wet rag this time should be better than spritzing the wood every few seconds. I have been practicing with cheap (relatively) flat sawn walnut for this project. I am glad I have, I'd rather be out 20 dollars than a few hundred from my bending escapades. I plan on using some quarter sawn mahogany my next project.
I can't thank you all enough for your help. Hopefully I can keep the break record to 6 sides.

You can practice bending on 1/16 plywood. It bends rather easier than most woods, but it's still useful for learning the technique. I'd have though $5 worth should be enough to get you going.

Galvanized steel pipe has a very rough surface which will prevent full contact and heat transfer to the wood. I think you would be better off with a black steel pipe.

I use to use a thin aluminum pipe but it did not seem to hold enough heat so I switched to a thick brass pipe and it worked much better.

Heating galvanized pipe to high temperatures can also give off semi- toxic fumes - don't do it indoors or drink some milk soon after.
I would not use steel wool in the end of the pipe. As Michael mentioned it can ignite, especially the finer grades of it.

I used a 3" truck tail pipe extension($7 pr *.00. Cut it in half, split one half, and shoved it inside the other half for thickness. Put an electric charcoal lighter in it, plugged it into a router speed control, stuck on a grill thermometer, and bend away.

I had not thought about the grill thermometer!

FWIW: I'm in the light spritzing camp. Like the others have stated, you need to be patient and wait for the wood to relax, before applying gentle pressure. I also think it helps to rock the wood slowly on initial contact with the pipe until the wood starts to relax, and slowly work towards the wet edge.

I use a 3" aluminum pipe with 1/4" walls, 500 watt halogen lamp, and caps on both ends (one of the caps is an oven thermometer). There's plenty of thermal mass and very good conduction of heat. A dimming switch allows me to dial in the temperature (425 F for me).

Just out of curiosity, how many canisters of propane does it take to bend a set?

Just out of curiosity, how many canisters of propane does it take to bend a set?

You can likely bend a couple dozen sets of guitar ribs with one little propane bottle....

That sounds like a lot of sets. I've never used a torch, but if I were to, it would probably take me a couple dozen bottles to do a set. <BG>

I just ran out on a bottle of propane. I bent 14 sets with that canister and did a few odd jobs with it as well.

Interesting posts about galvanized pipe, which I've used w/o problem since the mid 1970s. I don't think the relatively low temps I use for bending cause much poisoning of my system, but some may disagree based on observing me. Personally I'd be more afraid of Aluminum, which I don't use for cookware either. I choose relatively smooth pipe sections, so I haven't seen a problem with bumpiness.

I'd love to use all those fancy electric gizmos to heat the pipe with, but I'm off grid and rely on a solar/battery system. I try to conserve as much electrical power as I can where it's possible. A thermostat would be nice, but a little skill and experience can make it all work in less than ideal conditions.

Bob, I'm not sure if you are serious or not...
But I can confirm what Mario said. I used a torch and iron pipe for my first few guitars (maybe it was 5 or 6) and I still have that same cheep-o torch. Used it to sweat pipe joints when I re-did my shop. Still has plenty of gas in it.