Dovetails, whether they be through, hidden or blind, have been done for centuries, and been the sign of a craftsman. They have traditionally been done with a saw and chisel, which being straight dictate the way a dovetail is going to look, and that is with straight sides.
Leigh have used the router to create the Isoloc joint, and done it in six different profiles. The Isoloc joints is very strong and has a large surface area for glue up. Like a traditional dovetail, they go together only one way. A spiral upcut router bit is ideal due to the cutting action onto the side grain and then the end grain of the boards to make these highly decorative joints. Straight bits can be used for this job.
Isoloc joints were primarily designed as a variation of the half blind dovetail, yet with a simple jig adjustment, they become a talking point as they become a through dovetail. A further jig adjustment, and Inlaid and Shadowed joints become possible.
Six profiles on three templates are available for the Leigh D4R. This is the "B" template.
Joint fit for this jig is determined by the Variable Template Guidebush System (VGS), this is made up of an adjustable 3 piece guide bush. The guide itself is tapered, and its adjustment comes from winding it up or down, therefore increasing or decreasing the diameter of the guide touching the template.
A 1/8 turn of the barrel adjusts joint fit by a mere one thousandth of inch! The VGS guide bush system, attaches to the router in the same way the eBush does.