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Thinking about guitar design, I have another question for you all.

This is about the tail to neck taper, not "the wedge" design.

When I built my first guitar (and successive guitar too) I tapered the back from 2" behind the waist to the neck (top of the body).

Looking at my Takamine, they taper the back all the way from the tail to the neck.

How do you folks do this and why?

Some food for thought.

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Rod,

When I did my backs with ladder bracing and the length-wise arch had to come from shaping the sides I did it as Cumpiano shows in his book. Starting to narrow the sides from just behind the waist (lower bout side) and bringing it down to the neck. Then you sand a bit of an arch at the tail-block.

Since I've move to my X-braced backs, the bracing gives the back arch in all direactions and I just fit it on the sides tapering proportionately from the tail block to heel block - shaping the sides appropriately to match the back profile.

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

If you use something like a radiused sanding dish to finish off the side height, the location of the taper will sort of fall out 'automatically'. How much of a difference you see where in the side height has to do with a lot of things: the radius of the top and back, how much taper there is, and the curve of the outline and depth of the waist being important ones. A lot of rhetorical blood has been spilled on lists over the years about where the taper 'should' happen, but if you're going to retain a uniform back curve the shape of the side to back contour line is pretty much determined by geometry.

Discalimer: IAAM (I am a mathematician)
Given the thickness of the body at the neck and at the tail, any given back radius (if done properly) has to come out the same way on a fixed guitar profile. There's only one way to fit a sphere of given radius through two points 'straight on' (with both points on an equatorial line), and so this determines the side profile.

So, for example, given my guitar shape and the thickness at the head and tail the side profile here is the only way to get a perfect (and straight) 15' radius on the back.



Of course, not everyone's putting a perfect radius on their backs nor is there probably any real requirement for a mathematically perfect dome, so whatever approximation works best for you is the way to go.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services