Wednesday, October 22, 2014

Bending Acoustic Guitar Sides

Crafting an acoustic guitar is not only about design and acquisition of desired wood.  It's about tools necessary to accomplish the project in a way that is successful.

In my short tenure of building acoustics, I've learned one important thing.  You must either have a full piggy bank and a willingness to part with large quantities of cash, or the ability to create unusual tools necessary for a satisfactory outcome.

One of the tools of the trade is a side bender, which is used to form raw wood into the desired shape for a guitar body.  A heat generating tube is one method, which is used by many luthiers, and another more elaborate device is a side bending machine.  I've built both, but I think the 'machine' will work best for me.

The photo above is of the tube style side bender, which I designed and built several months ago.  As you can see, it's pretty simple , , , a heating element, controlled by a rheostat, heats the copper tube to the desired temperature, and the guitar side wood is hand-shaped around the extended tube.  There is a bit of trial and error involved with this type bender, and the final result can be irregular in shape.

The bending machine on the right is a creation I designed and completed today, which takes the 'guessing' out of bending acoustic guitar sides.

The design of my machine is similar to those used by other guitar builders, but I tried to take the best ideas from other machines and to incorporate them into a unit that would work best for me.  I'll try to explain why I designed it a certain way, and how it works.

It's a four-part creation made up of a base (the brown part), a body form, which sits inside the base, (this particular form is for a dreadnought style guitar), a specially designed retainer, which is located at the end of the screw press rod, is used to form the depression at the waist of the guitar side, and four spring-loaded retainers, which hold the raw guitar side wood securely on the form during the bending process.

Yes, those are light bulbs you see on the surface of the base, which are the heat source for the process.  The inside of the body form is lined with reflective foil, and the top is covered with a sheet of stainless steel.  The waist retainer rides smoothly up and down the slotted openings in the base, because of an embedded steel blade in the retainer.  The other movable retainers (the dowel rods are there to protect my hands from being burned on the heated surface during the alignment process) can be strategically positioned at bend points on the surface of the body form to hold the wood side in place during the heating and cooling process.

I chose light bulbs for the heat source, because a luthier with thirty years experience says it's the least expensive and equally efficient way to conduct heat to bend wood.  Another method is to use a heat blanket, but it's costly and requires more pieces to mess around with.  Due to the dreadnought shape, I chose to use a 100 watt bulb in the upper bout position of the bender; a 75w bulb at the waist; and a 150w bulb for the lower bout (this will equalize the heat in consideration to the distance of the wood from the bulb.  And, the temperature can be further controlled by a light dimmer on the face of the machine.  To further control the process, I added a simple-to-use kitchen timer to the face of the machine as well, to control the 'cook' time.

This photo shows the machine set up and ready to accept  raw side material for bending.

Raw wood material is cut to the desired shape of the side pattern (profiled), and sprayed with distilled water to adequately wet it for bending.

The moist side material is then wrapped in craft paper to retain moisture, and inserted onto the stainless steel bender surface, under another movable stainless sheet.  The waist position is marked on the raw wood so as to center it correctly with the waist retainer (the center mark can be seen through the vertical retainer slide opening).

When the desired temperature is reached, the movable spring-loaded retainers are carefully moved into position shaping the side as they are positioned.

The raw material is left to 'cook' for a specified time, and then it remains in the bender to cool down, before being removed to a body mold for a longer cure time.

Why did I build this contraption, which my wife says looks like something Frankenstein might have used in the lab?  Well, the reasons are not complex.  I could pay someone to bend sides for me ($50 a set), but that seems a little foolish.  If I can build a complete guitar, I should be able to build the tools necessary to complete the job.  And, a finished bender similar to what I just created, for about a hundred bucks, sells for $485-$590 on eBay.  It seemed like a no-brainer to me.  And, besides, I love the process.  I think I may have been a mechanical engineer in a former life.


  1. This looks like something out of a Jules Vern story. It is both imaginative and beautifully made, as is everything else I've seen on this marvelous site of yours. I'm gobsmacked.

    You say you are not an artist..? I disagree. Totally!

  2. Thanks for the comments Kerry, and thanks for visiting the site. My wife thinks the bender looks like something Frankenstein may use in the lab, or like it's some ancient torture device. Oh well, it serves the purpose as will be evidenced shortly with pics of the latest acoustic on the bench. I'm very fortunate to be able to accomplish some of the artsy things I attempt.