The book gets a little confusing with a mix of instructions for both, for steel string, and for classical. It helps to highlight all of the sections that deal with your project, and to print and tape in the revised stuff like the new neck block and all the errata stuff. Old habits from decades of military flying re: how to build a knowledge base...my copy is filled with notes, comments, reminders and stickies indicating where the book needs clarification or updating....take the time to go through and have all reference materials noted and posted helps a lot, and going through the process of posting all the updates will help you fam with the building order.

So just to address the question while avoiding comment on what might be alternatives:

- The body is initially profiled as two planes which meet about 2" below the center of the waist

- The lower bout plane is level with the top and the upper bout plane tapers from tail depth to the neck depth

- After smoothing the intersecting planes with the sanding jig in Fig. 10-5, the steel string gets the back linings installed and additional facets are sanded in at the head and tail per Fig. 10-10a & b

- Once that's done, a head block to tail block back arch is refined using a continuous pass with the big sanding fixture...this is what results in the longitudinal arch and smoothing of what was the pronounced intersection of the upper and lower bout planes

- Some sanding of the sides near the head block and tail block must be done to accommodate the rise in the back near the neck and tail block...this provides something close to the radius cut by a radius dish, but unlike that method, the extremes of the upper and lower bout and the waist remain flat. You want to spend some time reading this step (pg. 230, IMS), as too little and you get a weird little dimple in the back, and too much a hump.

I know just what you mean. It bothered me also.

Now I follow the Cumpiano procedure to get the sides ready then I finalize the rims with a radiused piece of wood and a sanding block. You can see where you need to round the rims slightly to match the radius. I use 16' on the back and 28' on the top. I leave the sound board flat from the end of the fingerboard to the heel. Sand paper could be put on the bottom of the radius board and used like a shaped sanding block.

I do it like this

I do like this idea. Curious why not just apply sandpaper to the radiused piece of wood? Is there any reason why you couldn't do this?

Anyone have any idea what the actual radius is on Cumpiano's guitar? And what is a good way of converting a known radius (say 16') to an arc on a 2' long board? It would be a bit hard to find a 16' compass and area to do this in.

I do like this idea. Curious why not just apply sandpaper to the radiused piece of wood? Is there any reason why you couldn't do this?

Anyone have any idea what the actual radius is on Cumpiano's guitar? And what is a good way of converting a known radius (say 16') to an arc on a 2' long board? It would be a bit hard to find a 16' compass and area to do this in.

16' rope taped to the floor with chalk on the end.

16' rope taped to the floor with chalk on the end.

what bothers me and i hope someone can put me straight (sorry for hijacking the thread but it is related) is; if you taper the back toward the headblock BEFORE installing kerfed lining, when you come to install them, do you have to break the linings at the point where the taper begins so that they follow the line of the rim?

For triangular linings, it's not really an issue, as there is very little loss of stiffness. For reverse-kerf linings, there is a significant reduction in the stiffness of the lining through that area, but whether that really matters once the box is closed is another matter. The bigger issue for me is one of appearance, so for reverse-kerf or solid linings, I'll try to keep things in one piece by going a bit deeper (3/4" versus 5/8") when milling up RK linings.

thanks for reply, Todd. So, do you glue the kerfed lining on before tapering the back? And so the kerfed linings become reduced in size as they reach the head block.

It's then fair to ask why someone building on a building board might not want to use a dish or a radius stick to handle the final radiusing of the back? That can and has been done - there's no geometry issues or structural reasons not to. My guess as to that the reasons why Cumpiano outlined the approach he did was that a) a true radius on the back would have required more in the way of tooling and skills, and b) using a longitudinal radius and correction at the blocks for dip/hump was good enough.

I like to choose methods that are easier and more accurate. Different strokes, eh?