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And have any links/pics?

No takers so I'll ask the obvious question............to me at least. What is a C block?
Tom

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A person who has never made a mistake has never made anything!!!

I think he means this, Tom. Or it's about guitar building while incarcerated in the big house.

Alex

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"Indecision is the key to flexibility" .... Bumper sticker

that is called a spanish block spanish foot etc common on classical pain in the foot on steel strings.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Ed, I've used one in the past, This is not the best photo but the only view I have of it. It works well, kind of a pain. I used blatic birch ply where my bolts go through, I just thought it's be better structurally.

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Jim Watts
http://jameswattsguitars.com

Thanks.

Do you feel the c block style helps prevent neck block roll/body distortion? Worth the extra effort?

Well, honestly I don't know. It seems like it should, but then again I haven't had any roll problems/neck reset issues that I'm aware of. It seemed like a good idea but it's definitely more work for unknown gain, at least in the reasonable future. I haven't done one these in a few years now and am currently just using an over sized neck block.

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Jim Watts
http://jameswattsguitars.com

I know right? Takes 15 years to know if the extra work was worth it...

After my first few builds caved into the sound hole, i said to myself "never again"
This is what I do now, no issues whatsoever since.
I rough these out at least a year before building with them.

Exactly that!

Holes marked for bolts?

Is the foot tapered to match the angle of the first back brace? Like does it butt right up against the brace and fit it perfectly?

The holes for the bolts are drilled with a 3/4" forstner bit (using a 1/8" pilot hole) before cutting the "C" out with the bandsaw and tapering the sides.
The bottom foot extends to butt up with the first back brace, and the top butts into the UTB.
I leave the 1/8" pilot holes until after the body is complete and neck mortice is cut - then match the layout to the neck tenon for the bolts, then widen the holes to 1/4".

I think I'll try one...

I do them on every guitar. I do think it helps. Wrapping it around the curve on the sides I think is just as important as extending into the first braces. They do butt tight against them. You can see I core out a bunch of wood from underneath, they do not weigh hardly any more than a standard block. I cut the mortise and the bolt holes before installation and use the mortise to align the sides etc...

I also make the upper bout of the back flat. I think that is just as important too. The way I see it if that radius flattens the neck block HAS to move out and affect the neck angle. If it flat then it has no where to go. The third and fourth braces have a steep radius, the back taper allows the back to have a compound radius and still look normal.

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Burton
http://www.legeytinstruments.com
Brookline, MA.

I use an extended 'chin' like that on all of my guitiars, but only use the 'foot' on Classicals, where it's expected. I use an 'A' brace setup, with two low braces that plug into the chin, go through the upper transverse brace, and inlet into the upper arms of the X on steel strings, or the waist brace on a Classical. When I used the chin alone it helped stability a lot, and the 'A' brace adds even more.

That's epic Burton!

Colin Symonds (Colin S on this forum) has a very well thought out c neck block system which is what I build with. See it here http://luthiersforum.com/forum/viewtopic.php?f=10101&t=28554&p=382081&hilit=neck+block#p382081

Thanks!

This is an important difference between steel-string design, and classical design. Going back at least 100 years, classical builders have created a back profile that has no longitudinal arching from the wide point of the upper bout to the wide point of the lower bout. No arching, no movement. The classical "slipper foot" carries the neck load to the upper back brace. The "C-Foot" is an important improvement for steel-string guitars. (It's not a bad idea for classicals.) An old idea is the elevated fingerboard--either attached or not. Combined with a slipper foot, the elevated fingerboard is the same as a "C-Foot".

Yes, I know, steel string tensions are much higher. The rules are different. But this is one area where steel-string builders could learn from the classical tradition.

Yeah, it's kind of silly that classicals use a flat upper back, which is strong on its own, but steels have it domed, where the foot would be really helpful to prevent it from flattening out.

A flat back could still possibly stretch longer over time too, but I doubt the force on it is concentrated enough to do it. Still, the foot is good insurance.

Most important to me is a strong upper transverse brace on the soundboard, and a headblock extension that is butted and glued to it. The brace needs to be thick as well as tall, because it's both resisting torque, and taking the compressive force that is coming in from the side of it (in line with the strings).

But there are other styles, such as the notched A frame, which aren't quite as strong, but probably strong enough. The most rigid upper bout in the world isn't going to stop the rest of the box from deforming over time... though double sides, solid linings, and carbon fiber bracing might

What classical guitar has a flat back, anywhere? I don't know one. However, I'm willing to learn. Mine are arched in both directions, though not done in a dish.

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Waddy

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Sound Clips of most of my guitars

Eric Reid wrote:
"No arching, no movement."
for clarity, do you mean 'no movement with changes in humidity' or 'no vibration'?

Dennis K wrote:
"But there are other styles, such as the notched A frame, which aren't quite as strong, but probably strong enough."
Why do you say the A frame is not as strong? You can still use as stiff and strong a brace as you want for the upper transverse brace, and the A takes the neck thrust directly.

I don't know if you can see it in these crummy photos, but with a straight edge resting on the back center seam, it is touching near the upper and lower brace, and very slightly concave in between. These guitars have normal "doming" across the back.






That last one is a Francisco Nunez 11 string from about 1895.

Some of these may have moved over the years, but that doesn't explain the 2008 Ramirez, or the two Eric Sahlin guitars I've had in the shop with the same back profile.

I talked recently with a young classical builder from Buenos Aires. The back profiling method he was taught would yield exactly this profile.

I'm not saying that everyone does it this way. Kohno, for example, built with a pronounced longitudinal dome. A 1911 Jose Ramirez "tablao" guitar I restored had extreme doming in both directions.

I like to build with a slight longitudinal dome on my own guitars.

I'm sorry Alan, I didn't make myself clear. I meant that a back with longitudinal doming, put under tension, can elongate by deforming. A cylindrical section stressed along it's axis can't do that.

It will move very slightly along its length with changes in humidity like any back. It will vibrate, as everything does. But its resonant frequencies will differ from a back with longitudinal doming.

Only time will tell, but it's possible to make some informed guesses. Wood creeps over time in some proportion to its initial deflection under load. A rule of thumb is that initial deflection is about half of the deflection after a year. From there on, the movement is very slight, but not insignificant. (Hence neck resets.) Obviously some pieces of wood move differently than others. Repeated wide swings of humidity will exaggerate creep. But careful measurements of initial deflection should give you some idea of the benefits of a C-foot. (And yes, I'm a believer--better longevity, and minimizes the need for "fall-away".)

Very interesting, Eric. I have never seen/noticed that in a classical guitar. I do know that some builders build flatter in the back than others.

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Waddy

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Sound Clips of most of my guitars