Q. What's the advantage of using a router fitted with a template guide bushing to cut hinge mortises? Why not just use a flush-cutting pilot bit and a flush-type template?
A. Gary Katz, a finish carpenter in Reseda, Calif., and moderator of jlconline.com's finish-carpentry forum, responds: Whenever I'm duplicating a shape with a pattern template, I generally like to use a pilot — or pattern — bit guided by a top- or bottom-mounted bearing that matches the diameter of the cutters.
An advantage of this setup is that the template can be made to exactly match the size and shape of the workpiece; there's no need to calculate offsets. And because the bit is going around the outside of the pattern, sawdust buildup interfering with the cutter is rarely a problem.
But when I cut mortises with a router and a template — for hinges, locks, and other hardware or joinery — I prefer to use a template guide bushing and a regular mortising bit in my router rather than a bearing-guided bit. This mortising method offers several advantages.
First, when you're cutting a mortise, the router bit must be inserted inside the template, so a template guide bushing protects the interior walls of the template from being nicked. Also, when you're using a template guide bushing, the template opening has to be oversized to accommodate the bushing's outside dimension, which is a good thing because sawdust waste builds up inside a mortise template. Having a template that's 1/8 inch to 1/4 inch larger than the mortise allows a little extra room for this waste, making it easier to cut mortises quickly and cleanly.
In addition, the template kits of some manufacturers feature template guide bushings that are easy to remove in mid-operation, making it possible to switch quickly from one bushing to another of a different size. This is something I do frequently, particularly when I need a mortise that steps down deeper once the plate size is cut (for pocket pulls and some flush bolts, for instance).
