Shimming the Dovetail Joint---Dovetails Revisited

[Andy Morton]

Hi builders...

Another dovetail question--and this has to do with shimming the joint.

1) Do builders glue the shims to the tenon and neck surfaces, sand/shave to fit the neck into the mortise, dry fit so everything is snug...and glue the joint (with all shimming and fitting completed prior to this step)?

or

2) Do builders fit the neck for gluing and then add shims for the final tightening and glue them in at the same time the entire joint is being glued (or if you see a void during the final glue up and then tap shims in the joint to snug everything up)?

I hope this question makes sense....I have studied numerous threads on this already and haven't seen anything that really speaks to this...

Thanks for any help!!!

Andy Morton

[sunburst]

Different builders do different things.
Most of the dovetail shims that I install are in guitars when I reset necks. I prefer to adjust the neck angle (by cutting the heel) until the geometry is correct, then glue shims to the dovetail tenon. After the glue cures, I shape the tenon to once again fit the mortise by carving away material from the shims.
If I'm in a big hurry and don't want to wait for the glue holding the shims to the tenon to dry, I fit the dovetail by shaving away shim material with the shims still loose, then glue everything together at once. That can save a full day when a customer is waiting for his/her guitar.
Some folks glue shims into the mortise then refit the dovetail.

On those occasions when I "miss" the fit of a new dovetail, mandolin or guitar, I once again prefer to glue shims to the tenon, wait for the glue to dry, then fit the dovetail.

I don't know of anyone driving shims into gaps. That seems like a substandard practice to me.

[fscotte]

I used to cut tapered dt joints, but moved to a straight dt joint for reasons which make it easier for me to mark the outline of the dt on the neck blank... but thats a different story.

I now create the tapered joint by gluing 1/32" ebony veneer shims on each side of the neck tenon. These come in packs already dewaxed and precisely sanded to the same thickness. The shims are only about half the length of the tenon. I slowly sand a taper into the shims until the joint becomes snug.

I like using ebony because when fitting, the tighter areas leaves black dust on the mortise.

[Andy Morton]

Thanks for responding---I have already put your help to use during an early sat morning session at the bench....I am getting there but with quite a bit of fine tuning -- sanding/filing/shaving with the chisel. I am using maple shims (leftover rim material) and now I appreciate the use of mahogany or walnut as shims (so much easier to sand/shave).

John---when you said that you shaved the shims while still loose...do you insert them in voids in the joint and get them nice and snug with the neck fitted into the mortise? And then glue everything for the final fitting. Is that what you mean?

Thanks!

Andy

[sunburst]

John---when you said that you shaved the shims while still loose...do you insert them in voids in the joint and get them nice and snug with the neck fitted into the mortise? And then glue everything for the final fitting. Is that what you mean?

I don't really like doing them this way, but sometimes time constraints are involved.
I start with two shims of even thickness. I chalk the sides of the mortise (I use "antique" blackboard chalk that is not dustless. Do some research on chalk fitting to know more about it), and I lay the shims in the dovetail mortise, one to each side. When I place the dovetail tenon in the mortise, chalk will transfer to the shims where there is contact. Depending upon the thickness of the shims, I can either start with a chisel and pare away shim wood where there is contact or use a scraper to shave away the shim wood. I lay the shim on the bench top with a stop at one end so that I can slice off a thin shaving with a chisel or scraper. Continue until the fit is good and glue the neck in place.
In a blind dovetail, like a guitar, care must be taken to assure that the shims, when they become thin, do not get out of place at the bottom of the dovetail and broken when fitting the tenon into the mortise.

I almost always use mahogany for shims because, as you have found, carving them is much easier than many other woods. I also check for grain run out and orient them for best carving.

[AndyV]

I used to cut tapered dt joints, but moved to a straight dt joint for reasons which make it easier for me to mark the outline of the dt on the neck blank... but thats a different story.

I now create the tapered joint by gluing 1/32" ebony veneer shims on each side of the neck tenon. These come in packs already dewaxed and precisely sanded to the same thickness. The shims are only about half the length of the tenon. I slowly sand a taper into the shims until the joint becomes snug.

I like using ebony because when fitting, the tighter areas leaves black dust on the mortise.

I like the point about ebony leaving trace markings! Thanks.

[fscotte]

Well I would assume mahogany would leave dust marks as well. If you use maple shims, it would be pretty difficult to see since its the same wood.

I think any hard wood is ok. I just used ebony because I had a whole pack of it laying around and you can get a lot of shims out of it.

I use a variety of tools to sand and scrape the shims down.

[John Kelly]

Would love to say that I never have to shim the dovetail as I cut it so accurately, but of course this is never the case. I generally glue shims to the tenon then use chalk as John suggests to mark and trim to a snug fit. I find it easier to work on the tenon than to work in the mortice when trimming the excess.