Saturday, February 9, 2008

LordLQQK: The Wood Bender

There are times, and many more situations, where you need to bend thin strips of wood to do your bidding.

One of my numerous projects is violins, shaker boxes, boomerangs, ok.....wait a minute I did say one. Ok, lets stick with violins. Along with the long hours that are spent on the faces and backs; planing with finger planes and scrappers, and gingerly shaping the thin quarter sawn spruce, there is the shaping of the ribs, or the sides.

Now there is a specialty iron that is used just for this bending, but that is about all it can be used for. If you want something wider or just bent differently, it is kind of a "one trick pony". That isn't a bad thing if that is all you are doing. But since I am rarely asked to make violins and I have other interests than "luthierism". I needed something that is going to do more than just make violin ribs.

Without going into a lot of detail on how to actually make violin ribs, which isn't the point of this, I would like to go into the details of the bending process. I prefer to use a propane torch shot up various diameters of pipe. For very tight bends a 3/4" galvanized gas pipe is ideal.

First thing I need to cover that this does use a flame. Great care must be used: proper ventilation, heat protection for the work surface, proper flame setting, proper equipment, and heat control.

List of tools:
BernzOmatic® Trigger Head, this is specifically used because it is one of the most inexpensive torches that can be used even upside down. It can be used with a Propane canister, or for much longer use periods, it can also be fitted with an adapter to fit it to a standard 20 pound propane tank.

A plumber's welding pad, this is used in between the pipe and torch and the workbench.
And a steel gas line pipe, preferably the silver galvanized steel type, the black pipe will mark the wood.
You will also need a piece of strap metal to attach the pipe on the workbench.

For the sake of storage I used a piece of 3/4" plywood as a base, about 18"x18". Place the plumber's welding pad, doubled up, on the 3/4" plywood. Screw in the metal strapping on one side through the padding. Screwing it down keeps it in place, and that is one less thing to worry about.

To make things a little more flexible don't screw down the other side of the strapping. Since you are going to be using varying sizes of pipes it is better to use a QuickGrip clamp to hold the other end of the strap to the welding pad. Just be sure to remove the pad off the clamp on the strap side, it will melt.

Set the selected sized pipe into the strap/pad and lock it down tight. The pipe should be at least 12" to 18" long and hang over the edge of the welding pad by 12". Connect the torch up making sure all connections are tight and there are no leaks, friction tape helps where needed. Set the flame to ultra low and place it inside the pipe. Make sure the flame doesn't go out, the flame needs air and a flow pattern. Make sure it is channeled up the pipe.

Next is the wood. The wood should soak for about 20 minutes, depending, of course, on thickness. Don't over soak though or the cohesion of the wood fibers will start to break down. Also the wood should be over cut by a couple inches so that you have wood to hold without getting too close to the pipe. Also a solid strap can be used to hold the wood but if you use a strap pay close attention as the water starts to boil out of the wood. See what I am talking about in a couple paragraphs.

After the soaking of the wood, start up the torch and get it set up. I added a couple raised screws to create a path way for the propane hose can help keep the torch placed in the right spot and to keep it from moving. Drip a couple drops of water on the pipe to test the temperature. The water should boil off but still cling to the pipe. The pipe shouldn't be so hot that the water sizzles off the pipe without really adhering to the side.

Take the wood and place it over the pipe. Hold it against the pipe until you can see the water boiling out of the wood. After it starts to boil out you can removed the wood and start to bend the wood. The wood takes on a more elastic form and after the wood cools the fibers will "harden" to hold its new shape. It is a good idea to have a form set up in advance to give the wood a set state in which to cool in. After the wood cools it should keep its form with little or no spring back.

Practice and enjoy just make sure you well ventilate the room and keep the flame as low as possible.



charger1966 said...

Lord, This is a very good way to bend the wood. I am going to have to try this the next time that I need to bend some stock. Keep up the good work

Brad Ferguson said...

Hey LL Great Post,
I've been toying with the idea of making myself an F style mandolin one of these days and the process is alot more like violin making than guitar making as there is alot of carving and shaping involved in the top and back, So I might just be picking you brain when the time comes. Talk to you in the chat room.

Vic said...

Hey Lord,

I can finally view your site! After I get some more things done in the shop, I'm planning to do something more with my blog. Up to now, I've only posted energy service information. I think I'll start clean and do only wood topics. I talk about the other stuff all day and most people don't seem that interested in saving their energy dollars(unless their bills are outrageous).

muddler mike said...

very cool, LL. A couple of clarifications though:

wrap the strap with the welder's pad when clamping with the quickgrip?

do you screw the torch positioning screws through the pad too?

I've seen this type of bending in an article before (although not explained as well) and it seemed as if the guy bent the wood as he was heating it on the pipe. You recommend heating it first, taking it off the pipe, and then bending it, or does it matter?



Lord LQQK at the WoodSmithy said...


No you shouldn't have to wrap the strap or use the welder's pad to insulate the strap. The clamps you use should be metal and not be too affected by heat, and the strap shouldn't get too hot anyway.

The screws you put in should be to hold the torch hose in place. They aren't going to get hot at all.

Really it doesn't matter if you heat and bend on the pipe or bend off the pipe. The wood stays hot enough and flexible enough that you can bend it for quite some time after removing it from the heat, at least 30-60 seconds.

I am planning on preposting this in a little over a month, after I finish my mirror project. At that point I hope to have pictures, if not video, on the whole thing. I didn't really have time to document things as properly as I usually would.