[4DThinker]

One lesson from teaching furniture design for the last 4 decades was that dovetail slots across wide boards could be difficult to slide all the way in. If a good fit the friction would increase the farther together the joint got, and often require a bar clamp to pull closed all the way.
After battling this with a few students projects I realized that putting a slight taper in the slot and on the mating dovetail end could greatly ease the assembly.
I've written up in my blog how I cut the slot with router and straight edge, a router table for the mating edge, and when using the CNC to cut both the slot and the dovetailed edge. The result is a French dovetail that slips together easily but draws tight all along the slot at the end. Tapering for a snug final fit can also apply to long dados.

My blog post about it: 4DFurniture
4D

 

[difalkner]

Many acoustic guitar neck/body joints are tapered dovetail for a precise fit.

 

[4DThinker]

Good example and thanks for posting it David. Over the decades we had a few students make guitars for their workshop 2 projects. Hand cut dovetail for the most part.
Tapering long dovetail slots just 1/16" or so is enough to make them slip together easily. The taper of the guitar neck joint could be less and still do the job. I'd love to learn the history of making necked instruments this way. Has this joint been refined/improved over time or does it vary depending on who makes the guitar?
4D

 

[difalkner]

Has this joint been refined/improved over time or does it vary depending on who makes the guitar?

There are a dozen or more variations everywhere from butt joint bolt-on to over engineered Rube Goldberg joints. The one I built has a mortise and tenon bolt-on and I'll likely do the next one that way, as well.

 

[JohnGi]

Tapered dovetails seem to be a specialty joint in European woodworking, but they were commonplace in Chinese furniture. Leg to apron joints in chairs or tables are instances where weight on the joint is expected to hold it tight. Long tapered sliding dovetails were a way to edge join two boards without glue. That's a nice illustration in guitar building, difalkner.
This splined miter joint in the upper corner of a cabinet is reinforced by a pair of braces with tapered dovetails to the top and sides.

 

[DrRobert]

Tapered dovetails are a well known, pretty old techique. But thanks for reminding us and helping some newbies.