Anyone in here done a dovetail M and T neck joint?

[kiwigeo]

Spent most of yesterday working on a dovetail M and T neck joint on my latest steel string. Got the mortise cut on the body without any dramas but getting the neck tenon to fit comfortably just isnt happening. Joint is ok at top but bottom of heel is loose...this means bottom of tenon needs shimming right? I guess its a matter of trial and error to find right spot for the shim on the tenon? Im using Stewmacs templates and matching dovetail router bit.

Any tricks of the trade or secrets to fitting dovetail M and T joints would be gratefuly appreciated.

Cheers Martin

[Malibu]

Gday Martin. I'm not up to that stage but I had a quick look at the Benedetto book which basicaly says that you're right in shimming with wood until it's a snug fit. Likewise, it also says not to depend on the glue to fill the gap and that the heel end should be slightly tighter.
Hope this helps :)

[Jackspira]

Hi Martin, someone told me once not to be afraid to use shims and I relaxed alot after that! I use maple veneer to shim when I need to and I don't think it makes the joint any the weaker. If the shim needs to be thinner than the veneer ( often the case) I stick the shim to the spot where its needed with a dab of glue, then after ten mins of so its stuck enough to scrape/ cut/ file down till it fits. I'm sure you'll find after you've done a few that you get a feel for it and seldom need a shim.
Don't forget that if you use titebond, or any other water based glue, that the joint needs to be a reasonably easy sliding fit, if its too tight the glue will grab it before its in all the way.
One other thing, you probably already know, but don't forget to leave a gap (roughly 3mm is usual) in front of the dovetail tennon. This is important to make sure that the tenon sits snug on its edges and is not interfeared with by the front surface. Its also good practice as it makes it easier for anyone in the future to get steam into the join to undo it.
Jack

[gratay]

ah yes can be a bit frustrating the ole dovetail.....
when a dovetail is fitted correctly you should be able to tap it in with a hammer and need no glue and the neck won't pull forward under string tension and theres no shims....thats in a perfect world....

martin, if you tap it in and the neck tenon is pretty flush with the face and you can pull the back of the neck up with simulated string tension( by grabbing around the nut area and bend the neck) then you will need a shim....

One trick of the trade is to use lead pencil to shade the entire area of the body tenon or shim and you will see when you bang the neck in and out where it is touching on the neck tenon by the lead pencil left on it..so you know what material to remove on the neck tenon........takes the guess work out of it

we used to use urea formaldehyde for gluing the necks in at maton..
there is so many angles to consider when fitting a dovetail and adjusting one affects the others so its a bit tricky to do with words but anything i can explain to you i will try..
make sure you back-cut the shoulders of the neck but you'd know that...to get a perfect fit on the shoulders of the body

And what jack said about the bottom of the neck tenon is one that can be easily overlooked when your wondering why its got gaps on the shoulders...the more that comes off the neck tenon the deeper it will sit in the body so sometimes the bottom of the neck tenon needs some taken out to stop it bottoming out creating gaps where the neck sits on the body.......this has you scratching your head sometimes when the joint is tight but it hasn't pulled down onto the shoulders of the body.
I'll keep an eye on anything more you can add.
grant

[kiwigeo]

Wow, thats a stunning response to my query. Thanks guys.

A blazing hot day here in Adelaide so M and T work is on hold....no good getting hot under the collar struggling with an M and T neck joint while its 30 degrees outside and not much cooler in the workshop. Gotta get an air conditioner fitted.

Will post progress reports on the on going M and T adventure as it unfolds.

Cheers and thanks again Martin

[kiwigeo]

Okay a progress report for you all. Neck number one got tossed int the scrap bin and I'm currently fitting neck number 2. Things going a little bit better with the current attempt. The tenon is basically done and right now the glue is setting on the heelcap. Tomorrow final shaping of the heel area and headstcok will get done and hopefully the neck will get glued up.

[gratay]

ouch.......it may come in handy with another body...??
for shims i use a wafer rock maple the full length of the body tenon.....which you can thin out on a linisher w/ a hard block

you shouldn't have to throw it out....1 or 2 shims is not uncommon on guitars

[kiwigeo]

Hey there Grant,

Im using veneer for shimming. I ended up using four shims glued to the tenon. I modified your suggestion to use chalk to mark high spots on the tenon and used carbon paper wrapped around the tenon with carbon side facing in....it worked well.

[gratay]

hey Martin, Glad its working out ...

To give you an idea about the shims ....what we used to do was not glue the shims in as such......until the neck is actually fitted.

so if the neck needs a shim for whatever reason... cover the shim in lead pencil , slide it in between neck and body.......bang the neck back in ...then out to see where the pencil marks are....
this way your always just adjusting the neck tenon to fit ..because the shim is essentially just making the body mortise smaller

once the neck is fitted then glue the neck in by applying glue to the wall of the body mortise and then put your shim in, more glue on the shim and neck.....then bang the neck in....

I just realise I'm calling everything a tenon ...i don't know which is the mortise and which is the tenon so its all tenon to me.....
anyway thats a brief sort of description of how we all were taught to use shims

[kiwigeo]

Grant,

The tenon is on the neck and the mortise is cut into the body. I believe technically the joint we're talking about is a half blind dovetail mortise and tenon but no doubt someone with more experience in joints than me will correct me.

Maybe if you could reword your last post using the above defintion it'd be really helpful...ie are you trimming the tenon or the mortise? Your experieces working with M and T neck joints is most valuable and highly appreciated.

[gratay]

even though my experience in the past has been fitting dovetails ........what I'm setting up to do at home first up is bolt-on mortise and tenon....

because i want to be able to finish the neck and body separately for ease of any future repair or warranty ....this is obviously with a view to sell instruments..which is a long way off in itself, but something i have considered..

But if i actually think that a dovetail sounds better then i will go with that down the track......but i doubt that will be the case ...theres so many other factors to the end result be it bracing,finish,glue etc etc

[JackG]

I agree with Gratay why going trough the trouble of a dovetail and the complexity of manufacture and adjustments, it seems to me that a straight mortice/tenon with 2 bolts is a lot simpler to make and adjust.

What are your motivations (outside of tradition) to use a dove tail joint ?

Cheers
Jack

[kiwigeo]

Jack my motivation is three fold:

1. Tradition
2. At some stage someone is going to hand me an instrument with a dovetail neck joint that needs resetting.
3. Alot of people who buy hand made instruments prefer a dovetail M and T neck joint....dont ask me why, perhaps they just like to know the the luthier has sweated for hours getting the joint right and they're getting their moneys worth.

Cheers Martin