Dovetail Joint ?

[Eric Hochberg]

Hey luthiers and builders - are dovetail neck joints being used in today's basses, or is that a thing of the past? This came up in another thread and I'm curious.

[Eric Rene Roy]

I think the difference here is in the details. All neck sets that are done right are dovetails.

Engelhardt's, like Kay's, have a mechanically cut dovetail using male and female router bits. Unfortunately these usually have more glue than mechanical working holding everything together.

The "dovetail" I was taught in violinmaking school is a description for the flaring of the heel at the bottom (end-grain). This should be chalk fit and as perfect as you can get it. A well done neck set should be able to almost hold string tension without glue. A poorly done one is relying on glue alone. I did a YouTube video on a joint that failed on a Mathius Thoma.

I don't think poor fitting neck sets by design so the necks break out cleanly if put through trauma is a goal of any builder. Poor work is poor work, period.

[Eric Hochberg]

Originally Posted by Eric Rene Roy

I think the difference here is in the details. All neck sets that are done right are dovetails.

I guess I don't understand what a dovetail is, then. I thought it was a join as you describe for the kay/englehart, with an angled "key" fitting in an angled slot. I believe my old Czech bass has this. I thought it was more common now for the slot/key join to be 90º? Sorry I don't know the proper nomenclature for this...

OK, watching your American Standard neck replacement video, it looks like you changed the original angled slot to 90º(?).

[George700DL]

Originally Posted by Eric Hochberg

I guess I don't understand what a dovetail is, then. I thought it was a join as you describe for the kay/englehart, with an angled "key" fitting in an angled slot. I believe my old Czech bass has this. I thought it was more common now for the slot/key join to be 90º? Sorry I don't know the proper nomenclature for this...

When I was making my neck and deciding on the joint type, I saw the mini dovetail tenon on the bottom of the Kay neck heel, and I thought it's unnecessarily complicated. So instead I just have a simple dovetail joint just like on a violin or classical guitar - the neck block mortise is angled, but only slightly (bottom of the slot is a little wider than the top), and the neck heel is shaped to fit. That is a dovetail from the perspective of woodworking, but I'm not sure if it qualifies under that term in the context of luthiery.

George

[Jake deVilliers]

Originally Posted by Eric Hochberg

I guess I don't understand what a dovetail is, then. I thought it was a join as you describe for the kay/englehart, with an angled "key" fitting in an angled slot. I believe my old Czech bass has this. I thought it was more common now for the slot/key join to be 90º? Sorry I don't know the proper nomenclature for this...

Seems like most basses have a plain mortise and tenon joint like a violin or cello. Kays and Engelhardts have a French dovetail much like a steel string guitar.

I've never worked on a European DB with a dovetail neck joint, so I've assumed that Kay copied Martin and Gibson when designing their instrument.

Here are a couple of photos of a 1940 Kay neck joint, freshly disassembled.

[George700DL]

Originally Posted by Jake deVilliers

Seems like most basses have a plain mortise and tenon joint like a violin or cello. Kays and Engelhardts have a French dovetail much like a steel string guitar.

I've never worked on a European DB with a dovetail neck joint, so I've assumed that Kay copied Martin and Gibson when designing their instrument.

Here are a couple of photos of a 1940 Kay neck joint, freshly disassembled.

Maybe I just got tripped up by the terminology: I thought that any mortise and tenon joint where the sides are angled is called a dovetail joint.

In my case of my bass, the taper of the neck from nut to heel (when looking at the neck from bird eye view with the bass laying on its back) is just extended all the way to the bottom of the heel, so the sides of the joint slope at the same angle as the neck comes in (from the bird eye view). I guess this is how it's done on all violin-family instruments?

Or is there a type of a joint on a DB where the mortise and tenon are straight (sides parallel)?

George

[Eric Hochberg]

Heard from Arnold S on the other forum and he replied to my question, "So, a dovetail has the angled slot, and a mortise has a 90º slot?"

"Not exactly; the sides of the mortise are usually about 2 degrees off vertical, like the sides of the neck. This helps hold things together, and it allows the neck sides to be at a constant angle (think of the neck's taper--wide at the bottom, narrow at the nut)."

[Steve Swan]

We have an old ca. 1900 tyrolean bass in for a neck reset. It looks like it has a dovetail joint. When the neck comes out this week we'll know for sure.

[tstone]

I think some here may be using the same terms to mean different things. As I see it, a neck joint can be dovetailed, or it can be tapered, or it can be dovetailed and tapered (see sketch -- angles exaggerated for clarity.

The joint that is both dovetailed and tapered has the advantage that it not only has some mechanical strength in the absence of glue, but the fit also tightens as the neck is tapped or clamped into place, thus reducing any dependence on the gap-filling properties of the glue.

I always thought this type of joint was the common practice with double basses. Perhaps someone here can enlighten us if that is not the case.

[gbaker]

Originally Posted by Jake deVilliers

Seems like most basses have a plain mortise and tenon joint like a violin or cello. Kays and Engelhardts have a French dovetail much like a steel string guitar.

I've never worked on a European DB with a dovetail neck joint, so I've assumed that Kay copied Martin and Gibson when designing their instrument.

Here are a couple of photos of a 1940 Kay neck joint, freshly disassembled.

Timely post, I was just looking at changing a blockless DB to a block and mortise and was about to search for ideas.

The Kay joint appears to be tapered (kind of mandatory when the toe of the neck is) and a dovetail. Should be a good joint but is is apparently not since many Kay necks suffer from the "Kay break", a shear break about 1/3 back. It this because the neck is plain sawn (rather than quarter) and/or the mortise is not deep enough (not enough neck cross-section) to resist the force?

A German bass I repaired last year had a straight-sided mortise and I kind of liked the idea of it being, upon neck trauma, weak enough to fail at the mortise glue-line rather than splitting the neck or the block.

Ideas?

[Jake deVilliers]

Originally Posted by tstone

I always thought this type of joint was the common practice with double basses. Perhaps someone here can enlighten us if that is not the case.

That's not the case. I posted pix of a Kay French dovetail this morning. The usual arrangement is a very slightly tapered mortise and tenon.

[Jake deVilliers]

Originally Posted by gbaker

A German bass I repaired last year had a straight-sided mortise and I kind of liked the idea of it being, upon neck trauma, weak enough to fail at the mortise glue-line rather than splitting the neck or the block.

Ideas?

I agree. Its usually easier to repair an open joint rather than a broken neck. I like that the front of the tenon touches the back of the mortise too.

[tstone]

>> The usual arrangement is a very slightly tapered mortise and tenon.

So is the mortise and tenon joint tapered in both directions, i.e., both along the axis of the neck and perpendicular to that axis?

Or, to ask the question in another way, with the understanding that the angles would be very moderate, does it look more like sketch 1, 2, or 3 in my last post?

[Jake deVilliers]

Originally Posted by tstone

>> The usual arrangement is a very slightly tapered mortise and tenon.

So is the mortise and tenon joint tapered in both directions, i.e., both along the axis of the neck and perpendicular to that axis?

Or, to ask the question in another way, with the understanding that the angles would be very moderate, does it look more like sketch 1, 2, or 3 in my last post?

See Post #7 above.

[tstone]

>> See Post #7 above.

Thank you, that explains the taper in the direction along the axis of the neck. How about in the direction perpendicular to the top plate? In modern practice, is the mortise tapered in that direction as well?

[Jake deVilliers]

Originally Posted by tstone

>> See Post #7 above.

Thank you, that explains the taper in the direction along the axis of the neck. How about in the direction perpendicular to the top plate? In modern practice, is the mortise tapered in that direction as well?

There is no taper along the axis of the neck except with Kays and Engelhardts - see website for pix of Kay.

The very slight 2 degree taper is on the perpendicular plane.

[tstone]

>> There is no taper along the axis of the neck except with Kays and Engelhardts - see website for pix of Kay.
>> The very slight 2 degree taper is on the perpendicular plane.

I see. So if I understand you correctly the neck tenon looks something like the sketch below?

Thanks for your patience.

[Jake deVilliers]

Not quite. If you take off that little extension, that's what we're talking about - its just the whole butt end of the neck. You can see the mortise and tenon of a cello here: http://www.jjsviolins.com/rest01.html and a complete block replacement and neck graft here: http://www.stringrepair.com/Double_B...Neck_Graft.htm

[tstone]

>> Not quite. If you take off that little extension, that's what we're talking about - its just the whole butt end of the neck.

Interesting. I can see having such a wide mortise on cellos, violas, and violins. Because on those instruments, the upper bout ribs intersect the neck at about a 90 degree angle, so the neck block can be wide enough in the mortise area to have plenty of 'meat' on each side of the tenon and thus support the joint well.

But on basses (especially those with sloping shoulders), where the ribs intersect the neck at a steep angle, such a wide mortise would cause the upper corners of the neck block to be thin and pointy, thus quite weak and incapable of offering much support to the joint.

So I don't doubt what you are saying, I'm just surprised that this is standard contemporary practice. It seems to me that having what a cabinetmaker would call 'cheek cuts' on either side of the tenon would make the whole joint more robust.

[Jake deVilliers]

If you'd take the trouble to visit the second link I posted and look at some of the photos, you'll see a giant honking neck block in there which is where the 'robust' comes from.