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Spreader Jacks for Inside and Adjustable Forms

June 08, 2020

Spreader Jacks for Inside and Adjustable Forms

Not all luthiers utilize these handy jacks as they are used to hold the pre-bent guitar sides tight against an inside form. Also, if you use either our Adjustable Inside Form, or Side Forms, you will want to use spreader jacks with these forms as well.

I do use the inside form and I love it for many reasons. I won't go into that right now as that will be another article, but I can say that I feel an inside form has simplified the building and fitting processes quite a bit. So if you use an inside form you will want to make a set of these Side Spreader Jacks

Two or Three Jacks?:

Usually 2 will do the job. It really depends on how long the sides have been in the bender. Shorter times in the bender require more support in the inside form. Still, a spreader used at the waist is seldom required. Also, if you build our bending system, it will take very little pressure to keep the side tightly supported in the form.

Spreader Jacks Before Assembly
Spreader Jacks Before Assembly

Spreader Jack Modifications:

Spreader jacks are are usually made with square ends, but fully assembled. Mark yourdesired upper and lower bout curvatures on each block, using a top template. Then you can sand or cut carefully to the pencil line and sand smooth. Here in our shop we use a disc sander to sand the contour on each block. You can easily cut or sand the contours on the assembled jacks, but if you want to take them apart, you can do that too. See the assembly and dis-assembly instructions below.

Removal of Wood Blocks From Turnbuckles:

We assemble all of our spreader jacks from solid wood, with hardwood dowel pins. No glue is used to hold the pins in place. The dowels used are 3/8" diameter for the 3 largest sizes of spreader jacks and 1/4" dowels for the smallest one. To remove the dowel, place the wooden end so the face is solidly supported and the dowel can be pounded freely out. We use our woodworkers vice, cracked open about 1/2". To knock the dowel out, use a 3/8" (or 1/4") x 2" or so long blot. Use a plastic tipped hammer and the dowel should come out quite easily. Don't use too much force or you risk collapsing the wood face.

Replacing The Wood Blocks on the Turnbuckles:

Key for doing this is to place the wooden block on a very stable work surface without any bounce. The best place I've found the my cast iron table saw top. Place a slight chamfer on the end of the dowel with sandpaper. Insert the dowel and tap to start the dowel with a plastic tipped hammer. Insert the turnbuckle end into the block and align the eye with the dowel hole. Use more force as you progress by pounding the dowel into place.



Using The Jacks:

You will find that using these jacks is a pleasure. They are quick and easy to both install and to remove. Build your Spreader Jacks  in good woodworking tradition by finishing them off as a tool you would be proud to show off in your shop. Usually since the span of the face of the jack is so short, you can use them on practically any shaped guitar.

One Last Thing:

It is always good practice to have a spare spreader jack to fit to the waist. Even though it may not be a part of your standard instrument building regimen, a waist spreader can come in very handy when you need one.

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