My first dovetail jig was the Stots dovetail template master. It's now sold by Milescraft. You basically make a Keller style jig for what ever length you need. It works fairly well. I later found a nice aluminum keller set at an estate sale, so this jig doesn't see much use anymore.
DovetailTemplateMaster - Milescraft
The keller jig will cut through dovetails on long projects according to their literature, but I haven't tried that.
Keller dovetail jigs: Simple, fast & accurate woodworking tools
DovetailTemplateMaster - Milescraft
The keller jig will cut through dovetails on long projects according to their literature, but I haven't tried that.
Keller dovetail jigs: Simple, fast & accurate woodworking tools