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I see lots of luthiers doing this, but none of my plans show it.

What's the purpose? What considerations must be made to accommodate the design?

What neck block?

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Steve Smith
"Music is what feelings sound like"

Photo missing.

Photos are there now.

It's to make the region of the guitar under the fretboard extension stable and prevent the dreaded hump. I use one of those and glue my extension normally. You can also make a double mortise and bolt on the extension.

Note: depending on how much and where you're doming the top you might need to leave some material on the top of that piece as it will be higher in the dome, similar to the waist.

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Pat

What Pat said it's to stiffen the upper bout and belay, hopefully the eventual folding of the neck into the body necessitating a neck reset.

When you look at a guitar head on from the front and it needs a neck reset I can usually see it because the lines of the bindings where the body meets the neck turn inward as the neck is folding into the body. You can see the body deformation if you look carefully.

These "paddles" couple the block, sides, top and for some makers the upper transverse brace into one assembly pushing back on the tendency of string tension and time folding the neck into the body.

I worked on a Martin D-28 Modern Deluxe last week that has a paddle and that new 4 mm truss rod I posted about here on the OLF. So even Martin is using paddles on some models these days.

Is it a good idea? Not sure. I don't see any harm beyond any possible sparkle and tone in the UTB (upper transverse brace) region being dampened by the additional stiffness. Many would argue that there is no tone to be had or preserved in this region. They may be right.

My guess since we need time to know is that it's probably a good idea.

I'll add since this is pictured on a cut-a-way. Did you folks know that with the advent of the cut-a-way it's possible that we are seeing the need for neck resets sooner? I don't have the data but I have seen on my bench cut-a-way guitars that it's neck reset time and unusually the neck is now not just folding into the body it's sideways angle has changed... as the cut-a-way side has collapsed far more than the non-cut-a-way side. I had one on my bench from a major maker like this that was only 3 years old.... and it needed a neck reset.

This is rare, no need to worry about cut-a-ways but if I were building again I would likely be keen to use a paddle on a cut-a-way just in case anticipating that the asymmetrical structure may not resist folding as uniformly as a symmetrical structure.

If you use a paddle be sure to do dry runs with truss rod access to be sure it's accessible and be sure to put a hole in your UTB. You would be surprised at how often that hole is forgotten....

I use a 1/2” birch ply paddle on top of my neck blocks. My reasoning is as Hesh stated to tie the neck block to the transverse brace which in turn has ‘A’ braces to the X brace. On cutaways I leave a ‘foot’ on the bottom of the neck block to further support the cutaway. Just trying to keep things stable over time. Truss rod slot got routed after this photo.

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Steve Smith
"Music is what feelings sound like"

The main point of the paddle has been pretty well painted by the above participants, but I’ll present two more possibilities to ponder:

1. John Arnold shared here on the OLF a few years ago his suggestion of adding a trapezoid shaped patch of wood between a normal head block and the upper transverse brace, grain running parallel to the top, wedged snugly (no gaps at either end). It replaces the popsicle brace. It adds a lot of what the paddle adds, but it can be stuck in during otherwise normal construction (top glued on before back).

2. Whether you do the paddle or the patch, it is worthwhile to consider the downside of making the sides of the thing parallel. Having the sides parallel means they also run completely parallel to the grain of the top. That might increase the chances of cracks in the top. Hence, the trapezoid shape of the patch suggested by John Arnold, and why I flare out the sides of the paddle a bit when I build that way.

... why I flare out the sides of the paddle a bit when I build that way

Makes sense.

_________________
Steve Smith
"Music is what feelings sound like"

If the extension goes out past the fingerboard edges on either side it might help to prevent shrinkage of the ebony from pulling cracks in the top on either side. That's what the 'popsicle stick' brace is supposed to do, but doesn't do very well. I make my extension just a little wider than the fingerboard at the sound hole end, and wider at the base of the neck, so the edge doesn't run along a single grain line and concentrate the stress. I've done this for 25 years or so, and it seems to be working so far.

I've also been using 'A' braces, about 1/4" square or a bit more, on either side of the sound hole. The upper ends of these plug into the neck extension. The UTB is notched so they can run through it, and the lower ends plug into the upper arms of the 'X' brace on steel strings, and the the waist bar on classicals. I use a patch of (usually) spruce around the hole to approximately double the thickness of the top there, with the grain running slightly across the top grain; about 3-5 degrees, to help avoid cracks there. The 'A' braces taper to the height of the doubler at the lower end where they are inlet into the brace. All the bracing around the doubler fits tight. All of this is meant to keep the neck from shifting in in case of accidents. I've had two with this set of features that I can remember that have been knocked over or pushed off a table so that they hit on the back of the head or on the neck. Both had large dings in the neck/head, but no further damage. I'm sure, from prior experience, that they would have pushed in otherwise. I hate having to fix stuff I've made...

Thanks for the great explanation.

Do you have any pictures of this setup?

Martin began using the L-shape neck block (with 'paddle') when they implemented adjustable truss rods in 1985. I have seen Martins without them in later years (most notably the Authentics), but they are more common than not on most models since.
There are a few issues with the original Martin 'paddle'. First of all, it is solid mahogany like the neck block. It is not the best orientation of the grain, which is parallel with the grain in the neck block. That allows distortion under stress, since wood is not nearly so stiff across the grain. Martin would also leave a gap between the paddle and the upper transverse brace, which can allow the neck block to shift if the top cracks. The paddle's other function was to support the end of the aluminum channel truss rod, since the bearing washer and the rod could drop down, reducing its effectiveness. This issue with the truss rod was later resolved by crimping the channel so the rod could not drop when the rod is loosened. This function of the paddle was negated however, since the truss rod rout was larger than the aluminum channel to facilitate easy fitting of the neck dovetail. Another less than ideal feature of this paddle was the oversize rout for the flat 'popsicle' brace. The result was that the gluing surface to the top was limited to a very narrow band above and below the popsicle. Hardly enough to do much of anything.
The Martin redesign of the sub-style 18 models in the early-1990's included their version of A-frame bracing, which also had a laminated paddle style neck block. IMHO, that one actually served to reinforce the structure, instead of the mostly dead weight of the original design.

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John

Here's what I do.



The grain in the block runs parallel to the neck, and it goes almost up the UTB. It's a little hard to see the ends of the 'A' braces on the top, but the pockets in the block are clear. These should be a tight fit, since this is what keeps the neck from shifting forward. The added depth of the 'A' braces, and the added thickness of the doubler around the sound hole, do a good job of keeping distortion around the hole down.

The guitar is an oak Dread with a Sitka spruce top that I had at Woodstock a few years ago. The back braces are cherry, iirc, as is the neck. The block is butternut.