Official Luthiers Forum!

hi everybody,
currently trying to finish my first guitar, which is a CF Martin kit. the neck block and the tenon were made for each other. The fit was pretty good to begin with.

I got my dovetail joint fitting (what I thought was) perfectly before I sent it to get finished. when I pressed it in, it "gripped" and held. when I layed a straight edge on top of the frets, it landed right on top of my bridge, 3/8" above the soundboard. I was pretty pleased.

After I got the guitar back, the dovetail doesn't fit as well as it used to. It doesn't "grip" anymore. the fit is pretty tight, but there is a slight side-to-side shimmy (1/16" or 1/32"?), and once I do this, the neck comes loose. I wasn't sure what to do, so I sanded the sides of the tenon, and glued on slim pieces of mahogany, and did it over, re-chiseling the sides of the tenon using the chalk-and-fit-over-and-over technique.

it was going really well. as the tenon sank down lower in the mortise, I had a great, tight fit. but as the tenon got lower and my fingerboard extension got within 1/16" of the top, the fit got looser.

when I say, "looser," I mean that it doesn't grip as tightly, but, there is still a little bit of a grip. and the slight side-to-side shimmy comes back. it's better than when I started but still not perfect.

maybe my heel cap, the way it touches the finish is preventing a good fit? or maybe it's the way the fingerboard extension touches the top? I am stumped.

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"...you have to get over your strict adherence to your largely imagined notion of absolute perfection..."

You have to expect this. If you final set the neck when in the white , the finish will act like a shim. You need to scribe fit the neck . Once that is done you should be fine . You shouldn't have too work much to do.

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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

Thanks, John. what do you mean by scribe fit?

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"...you have to get over your strict adherence to your largely imagined notion of absolute perfection..."

I think he's saying with the neck in place to scribe a fine line around it, then remove the finish in that area.

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"Everyone wants to BE something, but nobody wants to BECOME something" - William Cumpiano

Some finsih likely is on the cheeks of the heel .... you need to re-floss the neck heel to improve the fit and tightness of the joint. I ahve to do this to all necks once the guitar is finished and buffed out. I alwyas se the neck as best you can in the white,then its not much to do once the guitar is ready to be put together.

now maybe others would .. but I would NEVER remove the finish under the heel on the guitars body ... why ???

1 - too easy to mess up.
2 - and most importantly - when the neck needs to be reset, the bottom of the heel (where it sits against the body) will get narrower on a tapered heel style neck ... and then you will have an area on the body next to the heel whcih is completely visible, with NO finish !!!


re floss it .....

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Looking at the second picture it looks like the top of the dovetail is a little small, you might want to glue on some more shims and keep the top of the dovetail a little bit wider. I'm sure that's the last thing you wanted to hear.

You never take off finish. What Todd said.

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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

I was thinking more under the fretboard extension, no?

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"Everyone wants to BE something, but nobody wants to BECOME something" - William Cumpiano

on my re-do, I got very close, so that the fingerboard extension was abt 2-3 mm from the top, and the side-to-side shimmy showed up.

should I only be filing from the inside of the tenon or something, at that point?

It seems like, if I'm very near the end, and I have chalk all over my tenon, indicating contact all over, it is impossible to know where to remove material from, to get that final fit. Is there a rule about this? I haven't seen it written about anywhere. whatever it is, I have been doing it wrong.

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"...you have to get over your strict adherence to your largely imagined notion of absolute perfection..."

When I'm that close I floss it for the final fit. Put some tape on the body of the guitar to keep from scratching the finish and work sandpaper in and out of the cheeks of the neck to allow it to go deeper into the body. The lets it sink right into place, and makes the neck cheeks fit tight against the body.

Disclaimer: I'm not an expert, this is just the way I do it.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

Yes the finish must be taken off under the fretboard. That isn't scribing. Scribing is making the heel fit the contour of the side over the finish. Pulling sandpaper between the joint usually will do the trick . You don't want a side to heel glue surface as it will make a bear of a time when you have to reset the neck.

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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

I'm wondering if I'm hosed.

Like I said, I got my dovetail fit really really close, just about to what I thought was perfect, and then I sent it to be finished. When I got it back, it didn't fit so well anymore, with a lot of slop.

Then I learn, all I had to do was floss the cheeks, and I'd be good to go. But I had put a couple of small shims in and made things worse.

So now I've sanded my tenon down, glued strips of mahogany covering the entire tenon on both sides, and am re-doing. now that I think I understand the dovetail better, I'm confident my fit might be even better this time.

but prior to sending the guitar to being finished, the top was masked, and I drilled holes for the low e and the high e in the top. when I finish this dovetail I'm worried that my saddle placement is going to move.

Am I hosed?

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"...you have to get over your strict adherence to your largely imagined notion of absolute perfection..."

I doubt you'll do anything except get the neck/body joint back to the position it was at before finishing. Reguardless there should be plenty of saddle to compensate for any difference. The difference if any should only be a few thousants.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

Does it make any sense that flossing the cheeks would make my dovetail get looser?

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"...you have to get over your strict adherence to your largely imagined notion of absolute perfection..."

Yes. Flossing allows the neck to slip further into the body (toward the soundhole). This will loosed the Dovetail due to the angle on the cheeks. It probably won't take much to get it to sink in correctly.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

thanks, I worked on it last night and I finally got it. I used slivers of mahogany and got it tight. the fingerboard was within 1mm of the top. so I smeared glue on the tenon and clamped that sucker down. let it sit overnight. after taking the clamps off, everything is still lined up, and straight. it feels good to finally be done with it.

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"...you have to get over your strict adherence to your largely imagined notion of absolute perfection..."