Death by Dovetail

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JohnFM
Posts: 2
Joined: Mon Mar 28, 2022 4:11 pm

Death by Dovetail

Post by JohnFM »

I am a first time builder (Martin OOO kit) struggling with the dovetail joint....I did the neck preset per John's video and was happy with it....Angle/Center/Elevation were set along with sanding the full neck and body interface for a common plane....I continued to finish the body, complete the fretboard, install the thrust rod and glued on the fretboard.....I checked the neck fit and alignment in a dry fit and all was in alignment.....I glued on the neck and the resulting glued joint was out of elevation alignment....the gap over the saddle was 5/32 and there was a small gap at the top of the heal/body interface....somehow the joint didn't pinch properly at the top part of the heel ....when I glued the joint, I slightly clamped the fretboard extension before clamping the neck....I thought this might have hung-up the pinching of the joint....so I decided to remove the neck and try again... I steamed off the neck and carefully cleaned all surfaces...I couldn't see any obvious obstructions....again I did a dry fit and it was good....held my breath and carefully glued it again starting with clamping the neck this time and then the fretboard extension.....same result....so I have again removed the neck and am now pondering my next move....I'm playing around with paper shims but so far haven't found a solution...any advise?
Thanks
John
Diane Kauffmds
Posts: 2846
Joined: Sun Mar 09, 2014 8:13 pm

Re: Death by Dovetail

Post by Diane Kauffmds »

Can you please post photos? It helps a lot if we can see the problem.

Now, if I understand, you've glued the fretboard to the neck, then set the neck. The heel has pulled up a bit on you? Plus, you have a bit more of a gap between the saddle slot and straight edge than we like to see. These are actually the result of 2 separate problems. Both can be corrected.

One problem is that the dovetail joint needs to be tightened, which I think you recognize. That's why the heel is pulled up.

The second problem is that you may have overset the neck a bit, resulting in the larger gap. With the heel pulling up a bit, I'd expect that you wouldn't have a gap, because the neck is Leaning forward. The fact that the gap is larger tells me that the neck is overset.

First and foremost, did you allow your joint to dry for a day or so after pulling the neck? Make sure you do, because if the wood is wet, you'll never get the neck to glue right. I made this mistake once, so make sure the wood is fairly dry.

Okay, after your joint is dry, install the neck again, as a dry run. First, put the straight edge down the fretboard and check that gap. Most likely, your neck is set too far back. To correct this, you'll need to take off a little bit of wood, from each cheek, towards the fretboard. I've made a drawing for you. Don't take off anything from the heel. You want the neck to lean forward a smidgen. You can do this by scribe sanding. Concentrate on the front 1/3 of the neck joint. See the photos.

Once you get the gap corrected and everything sits down, you'll find that the dovetail has loosened some. You can make thin shims, which will go into the joint, from chiseled slivers of mahogany. The easiest way to make shims is to buy some mahogany veneer, and cut strips out with scissors. Make them so that they fit each side of the mortise. Put one on each side, do another dry fit. You'll need to do this until the dovetail doesn't move when you pull the neck forward. The dovetail is a tight fit.

My guess is that although the neck sat down nicely for you, and seemed tight, if you had grabbed it and pulled it forward, there was movement. You have to pull pretty good to test a fit. When you add glue to the mix, it becomes more slippery.

Hopefully this helps, but photos would be very helpful. If you look at John Hall's neck reset videos, you'll see where he drops in shims. I'll see if I can't find the video for you.
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Diane Kauffmann
Country Roads Guitars
countryroadsguitars@gmail.com
Diane Kauffmds
Posts: 2846
Joined: Sun Mar 09, 2014 8:13 pm

Re: Death by Dovetail

Post by Diane Kauffmds »

At 7 minutes into this video, John discusses shims.

https://youtu.be/bJBsaac2uLU
Diane Kauffmann
Country Roads Guitars
countryroadsguitars@gmail.com
MaineGeezer
Posts: 1529
Joined: Wed Aug 13, 2014 12:14 pm

Re: Death by Dovetail

Post by MaineGeezer »

A few random thoughts, possibly useful:
Put some soft chalk on the neck dovetail, then assemble the joint, to see where you're getting contact with the body. Make sure it's not making contact at the very end, keeping it from fully seating.
When you clamp to pull the joint together, don't be delicate about it. Mash it together like you mean it. (On the other hand, don't break anything....)
Don't believe everything you know.
Anything is possible if you don't know what you are talking about.
When things are bad, try not to make them any worse, because it is quite likely they are bad enough already. - French Foreign Legion
Diane Kauffmds
Posts: 2846
Joined: Sun Mar 09, 2014 8:13 pm

Re: Death by Dovetail

Post by Diane Kauffmds »

YES! MaineGeezer posted information that I meant to post, but forgot.

The work is done by the front 2/3 of the dovetail, not the heel. Put lots of chalk in the mortise. You want to modify the dovetail tenon, NOT the mortise. You'll see where the wood is hitting. Sand the chalk away.

When the neck is set right, you'll hear the dovetail squeaking and protesting a bit. That's normal. I use a bar clamp to get that tenon into the mortise.
Diane Kauffmann
Country Roads Guitars
countryroadsguitars@gmail.com
Diane Kauffmds
Posts: 2846
Joined: Sun Mar 09, 2014 8:13 pm

Re: Death by Dovetail

Post by Diane Kauffmds »

YES! MaineGeezer posted information that I meant to post, but forgot.

The work is done by the front 2/3 of the dovetail, not the heel. Put lots of chalk in the mortise. You want to modify the dovetail tenon, NOT the mortise. You'll see where the wood is hitting. Sand the chalk away.

When the neck is being set right, you'll hear the dovetail squeaking and protesting a bit as you pull it in. That's normal. I use a bar clamp to get that tenon into the mortise, instead of hammering. You can hammer it, if you wish

Clamp over the neck block only. Do not clamp the heel!

There photos are of a guitar currently in the shop. I placed a bar clamp to show you where you should be clamping.
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Diane Kauffmann
Country Roads Guitars
countryroadsguitars@gmail.com
MaineGeezer
Posts: 1529
Joined: Wed Aug 13, 2014 12:14 pm

Re: Death by Dovetail

Post by MaineGeezer »

Also make sure the front face of the guitar body is truly flat.

And yes,modify the neck tenon only, not the mortise. I chalk the tenon, then see where the chalk has rubbed off it. Diane chalks the mortise, then sees where the chalk gets transferred to the tenon. Whatever works best for you.
Don't believe everything you know.
Anything is possible if you don't know what you are talking about.
When things are bad, try not to make them any worse, because it is quite likely they are bad enough already. - French Foreign Legion
JohnFM
Posts: 2
Joined: Mon Mar 28, 2022 4:11 pm

Re: Death by Dovetail

Post by JohnFM »

Thank you so much for the advise...I watched the video and it is very helpful...I will buy some mahogany veneer, chalk the joint and slowly work the upper part of the joint (wing)....I noticed in your photos and the video that you are clamping without a radiused caul on the fretboard....sorry, I can't seem to be able to attached any photos
Diane Kauffmds
Posts: 2846
Joined: Sun Mar 09, 2014 8:13 pm

Re: Death by Dovetail

Post by Diane Kauffmds »

I think you're havinh problems posting photos, because you're new to the forum. After you make 2 or 3 posts, you're posting won't require approval. Let me know if you still have issues.

I wanted you to see the clamp location on the neck block. It's easier to see it without a caul. That guitar had its neck, I wasn't really clamping it. I put the clamp on just to take a photo.

I have several clamping methods for necks. The easiest is the clamp as shown in the photo. After clamping the dovetail (as shown) I use 2-3 spring clamps on the fb extension, through the soundhole. Other times I use 2 bar clamps through the soundhole, to secure the extension.

I did a neck reset on a 1951 Martin D18. Here's a photo of the 3 bar clamps on it.
A caul is always a good idea. It doesn't need to be radiused.
PicsArt_12-10-01.18.35.jpg
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Diane Kauffmann
Country Roads Guitars
countryroadsguitars@gmail.com
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