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Side Bending Tutorial

4Side Bending Machine
This is probably the easiest way you will ever bend sides for your 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.

Here is the complete procedure:
 
Examine The Wood You Are Using For Your Guitar 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)

Marking The Sides For Registration

Mark Waist Centerline on Each Side
First, it is important that you lay the guitar 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


Make sure you have plenty of work area around your side bender, that your 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 Side Wood

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.

Assemble the Sandwich

Get the sandwich situated first. Begin by laying the bottom stainless steel slat on your work bench. Next place the wet wood side over the slat while aligning the wood with the stainless steel waist registration markings. The heating blanket should be placed so it is in contact  with the wood. Finally, follow-up with the top stainless steel slat. Place  a spring clamp at the lower bout end of the sandwich to hold everything together.

Anchor The Bender To Your Workbench

Lay down the bottom SS slat first,then the wood side to be bent, the heating blanket and finally the top stainless steel slat. Align the marker on the waist with the stainless steel slat.

Before you use the bending machine, it is best if  the feet of the bender are anchored to the workbench. I use a couple of quick-grip clamps to do this. An alternative is to place the bender in a woodworkers vice, but this requires the removal of the feet. Another option is to clamp in on the work bench with the vice and bench dogs. Whichever method you use, make sure the bending machine is secured and will not move. You will be working with extremely hot stainless steel and any slip of the bender can cause very severe burns.

Prepare the Bending Machine For The Bending Mode

Load the proper form insert into the machine and install the waist guide bar to lock the form insert into the bending machine. Crank the waist retainer up as far as it will go. Insert the sandwich into the bender and slowly crank the press screw down to squeeze the sandwich about half-way to the waist. The sandwich still needs be able to move for fine-tuning adjustment and registration.

Look through the guide bar slot on the bender and try to spot the registration mark you made on the side. Adjust the sandwich until the registration mark is centered on the channel.


Hook up the lower bout retainer with both extension springs. Do the same with the upper bout retainer. Next, hook up the waist retainer extension springs to the guide bar and crank the press screw until the guide bar just barely engages the form insert receiving channels (about 1/8” or 3mm).


 
Bending Machine in Bending ModeSlide the lower bout retainer about half-way around the form insert or until it stays in place without sliding back. Adjust the spring clamp at the back of the sandwich so the sandwich stays in good contact with the heating blanket. This will provide even and thorough heating throughout the entire wood side.

Now Move to the Upper Bout

Install a couple of spring clamps on the sandwich to provide good contact between the heating blanket and the wood side material.out. Place a spring clamp on either side of the sandwich so is has good contact with the heating blanket here as well. The bender is now ready for the next step - the heating mode.

Take the thermocouple probe end and insert it between the heating blanket and the wood side. This can be anywhere along the sandwich you can find an access space. Once you start the bender up you need to have good contact by the probe to accurately monitor the temperature.

Prepare Yourself Prior To Starting The Bender

Once the bending machine reaches its high temperature, the side, the heating blanket and especially the stainless steel sheets can be as hot as 350 degrees F. This means you can be seriously burned without any protective wear. Be sure to wear leather gloves on both hands and a long-sleeved shirt prior to plugging the bender into the electrical receptacle.