Official Luthiers Forum!

I just cut the rim open to expose the dove tail in the neck block. I noticed that there are two indentations on both sides of the dove tail. What are they for? Should I shape the rim to match these? (so far, I have not, wanted to ask first)

Mike

Could you be more specific?
I will assume you mean the jig marks on the newer Martin dovetails?

_________________
Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

Martin's neck blocks have a mortise in them prior to the machining of the dovetail. Ignore the little depressions that remain and fit to the angled dovetail sides......be sure to keep the male part long enough to extend beyond the remnants of the mortise into the bottom of the female tapered part.
The sides should be trimmed only to follow the straight angled recess.

HI Mike. If you're referring to the indentations toward the back of the dovetail, they are'nt for anything. They are just a product of the way Martin machines them. If you mean the two 1/4" holes on either side at the top, they are alignment/registration pin holes.

Hope that helps.

_________________
Don Sharp
Got Brazilian?
http://www.sharpguitars.com

Here is a picture for you - is your neck block like this one?



I agree with the others about the indentations in the dovetail cavity. It you mean the two holes on either side of the dovetail on the top of the block these are for alignment during assembly. You will see these holes on Martin tops too.

_________________
Ann Arbor Guitars

I always " guessed " the depressions in the dovetail on the Martin were to facilitate the movement of steam into that area when you are removing the neck.

Wow, that's pretty crappy. I haven't seen one of those yet. I guess it helps keep from splitting production of a part in to two lines - just route a dovetail in to a morticed block. So what if you loose the effectiveness of the most important part of the dovetail, toward the heel. That's a pretty substandard part - no way I would put that in a guitar I was building.

_________________
Eschew obfuscation, espouse elucidation.

Helping a yong guy with a Martin kit with the above neckblock. That "paddle" for lack of better word, cuz that's where I'd put a "paddle" or "extension" for double mortise & tenon neck joint... Their "paddle" has short grain and is prone to fail. It's milled out of one chunk of wood and is what it is... The paddle would be better suited out of void free plywood, or something like that. Sylvan Wells, John Mayes, myself, and a host of others like this double M & T method.

Yep. Never saw that one before. Those indentations would appear to be for the purpose of weaking the joint and making it more likely that the narrow part of the heel will pull away from the sides over time or upon exposure to heat.

_________________
Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Hesh,

Thanks for the picture... it shows what I was refering to. I was not taliking about the holes, but the indentions near the bottom of the dovetail. So, they are there for no real reason?

Mike

PS: David Collins, please post a pic of what you would reccomend. This part is a standard Martin part.

I had a neck block just like the one shown on a Martin kit that I re-set the neck on. I filled the two cavities with sawdust and superglue, re-attached the neck, and poof, strong as can be.

_________________
Jamie M

The neck block design has been around a long time. Is is a result of the CNC process. They run a flat bit to help clear wood. It is actually a good thing an won't hurt a thing. I have not seen a neck joint fail because of this feature.
The dovetail is a mechanical joint. The locking part is the wedge of the tenon ,and this pulls the neck tigher as the neck drops into the joint. Most people mess up the joint by not relieving the corners and this results in the joint being held off by the sharp corners.
john hall
blues creek guitars.

_________________
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

The problem I have with those leftover straight mortise hollows is simple lever mechanics. The further you get from the fingerboard, the less stress the dovetail has to bear to affect the same strength of the joint. If you lessen or eliminate the effectiveness of the last seciton of the joint, the upper portion has to bear a disproportionately greater load. The last 1/3 of the joint can bear the same load as the first 2/3 with the same pressure on the wood. Eliminate the last 1/3, and the first 2/3 has to bear 2x the load it would otherwise.

I know, that dimple did not fully remove the last 1/3 of load bearing surface of the dovetail, maybe more around 1/6-1/8. Still, when fitting a dovetail if there were any section that I would want to emphasize the the tightest fit, it would be at the end. I just see it as a completely pointless compromise of the joint. It looks to me like all they would have to do is not run the blocks intended for dovetails through the same CNC program as those destined to accept tenons. Even if so minor as to be insignificant, I see it as a compromise without any justification.

_________________
Eschew obfuscation, espouse elucidation.

Ok, I think I get the point. Sorry for stirring the pot! I'm gonna follow someones advice above and fill the dimples.

Mike

Mike, I say good for you for stirring the pot!

I'm with David. This is the most crucial part of the joint. But to play the devil's advocate, I would expect that Martin would have done extensive testing on the issue to keep warranty repairs down, especially on labor-intensive neck removals. Their 150-year-old reputation is at stake.

Also, there's not much force from the string pull being exerted on the the heel end of the joint. But still, I'd want to use as much of that glue area as possible.

_________________
now known around here as Pat Foster
_________________
http://www.patfosterguitars.com

Crucial or not much string pull?

The upper part of the joint is in compression--the dovetail faces there are not doing any of the work. The heel is a lever with its fulcrum toward the top. It's the part toward the back that is holding the joint closed; that is not coincidentally the place where separation from the sides is first seen.

_________________
Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Sheesh, of course, Howard! I had the 1:3 nut/heel motion ratio and the 3:1 force ratio mixed up. No food or caffeine this morning, waiting to get my blood test.

_________________
now known around here as Pat Foster
_________________
http://www.patfosterguitars.com