How to Use the GLS Side Bender

March 08, 2020

How to Use the GLS Side Bender

This is probably the easiest way you will ever bend sides for handmade guitars. The only drawback with this method is the labor that is involved to make the side bending jig and all the different form inserts you will be needing. You will need one form for each different sized guitar that you make, but with the time saved and the frustration of having to throw away tonewood, it is a welcome change. Bending sides with a bending machine gives you fast, consistent results and you soon will have a full compliment of form inserts in your shop - and if this is a serious hobby or a profession for you, you will have several bending machines as well. Note that this tutorial applies equally well to acoustic guitars, classical guitar, ukuleles, mandolins and hollow body electrics.
Here is the Complete Procedure:

Examine The Wood You Are Using For The Sides

Look for any end checking. This may ruin the whole piece if these checks are long and deep enough. Very shallow checks or checks that are short should not cause a concern as the sides are often trimmed enough during the butt trimming and neck routing operations. Thickness sand the sides to just a whisker over what their final thickness will be. This makes the side wood easier to bend, and saves you a bunch of time when finish sanding your guitar.

Try to use straight grained, quarter-sawn wood for the guitar sides. As you gain experience in working with and bending wood you will be able to graduate to the more figured woods which are not necessarily quater-sawn or straight grained in nature.

Before you use highly figured woods such as Bubinga with a waterfall grain, or some of the pleated or curly woods like Curly Maple or Curly Mahogany, you should have a bit of experience under your belt. One way to get this experience is to purchase or make a a few practice sides from inexpensive wood to try out your bending methods without sacrificing hundreds of dollars worth of exotic wood.

Sand Wood Sides to Thickness - General Recommendations:

Classical Guitars - 1.8mm (Final Thickness - Allow for some sanding after bending)
Acoustic Guitars - 2.0mm (Final Thickness - Allow for some sanding after bending)
Ukulele Sides - 1.5mm (Final Thickness - Allow for some sanding after bending)
Mark The Sides For Registration

First, it is important that you lay the sides on a workbench in book-matched fashion and fully understand how the grain patterns will look on the final product. If you are using a dark-colored wood, mark the center of the waist with a white pencil. Also, the waist centerline will have to show up very clearly on the side of the wood. The best way to do this is to place a small piece of masking tape over the edge at the waistline.

Then take a waterproof Sharpie Dry-marker and clearly mark the waist with a registration mark. In order to give you a little play while you are bending, make the waist registration line and edge mark about 1/2” (12mm) further from the butt end of the side. This will allow for a little movement which is usually the case when bending wood.

In order to keep the sides book-matched the registration marks should be on only one side of the wood. This will keep the sides book-matched - be sure to double-check this before you bend the second side so you don’t wind up with 2 left hand or 2 right handed sides. Not a very happy situation!

I also like to mark out the centerline of the waist on the stainless steel slats so registration of the slats and sides is very easy and any slippage is easily spotted. Again, the best method for doing this is with a water-proof Sharpie Dry-marker.

Prepare The Machine For Bending

Have plenty of work area around the side bender, and the work area is free of clutter and that you are working at a comfortable work height.

Preparing the sides for bending is very subjective, depending on who you talk to. Most luthiers wet the sides with a spray attachment on a bottle filled with distilled water, soaking them quite well, especially at the waist and bout curves. This is the only method that I utilize.

Other builders soak the sides in a tank of water for a few minutes and then immediately load them in a pre-heated bender. The objective here is to create steam when heat is applied to the wood, which makes the wood elastic and allows it to bend very easily around the form.

Thoroughly wet down the side wood with a spray mister, concentrating on the waist, and the upper bout curvatures. I like to spray both sides of the wood side with a spray bottle, then let the side set about ten minutes before spraying it one more time. This allows the side to absorb some of the moisture and aids in the steam generation to bend the side more easily.

For more detailed information refer to our Guitar & Ukulele Building Guide

Related Links:

Plans for making the Heated Side Bender - Guitar
Hardware Package for Heated Side Bender-Guitar

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