Official Luthiers Forum!

Hello all! After a post by Leerobs and my reply I got to thinking about
something and didn't want to hijack his thread so...I am in the middle of
making a jig that is similiar to the endgraft routing jig that people use
except that I will use it to rout the mortise as well (similiar to Robbie
Obrien). I used to use the stewmac routing templates and the fit right off
the templates was a little loose. I didn't mind because I would use shims
(veneer) to tighten it up and move the neck where I wanted. When all you M
and T users cut your joints do you leave them a little loose or do you try and
peg it right on? I still like the idea of leaving it loose and shimming but was
wondering what you all thought about that. I know that dovetails are usually
shimmed so I guess it shouldn't be a prob but what do you think? Thanks.

I make mine tight and just cut them both with a table saw (like Cumpiano shows in the book). If the neck is not on the centerline exactly, I'll sand one side and if necessary, shim the other.

M&T bolt on necks do not require a tight fit of the tenon to the mortise. It is the bolting torque the gives the neck its strength.

That said you would think it would be convenient if the tenon fits the mortise tight so that the tenon is a true alignment tool.

But the truth is in practice to get the centerline plane of the neck to match the centerline plane of the body, cheek adjustments are required that redirect the neck plane left or right as needed. This means the tenon must have room for some play so that these cheek adjustments will affect the centerline plane of the neck. If the tenon is press fit tight the flossing the cheeks would not move anything. Or would require that you shave the tenon on the oposite side tht you floss the cheek.

I make my tenon a good fit but not a tight fit.

We are talking thousands here not 64ths or 32nds

Oops I for got to answer your question I cut my tenon .005-.010 under sized. even then on occasions I have had to thin the tenon to allow for cheek fitting. Once I have the cheek fitting done if it is near being sloppy I will shim.