Last summer I built a set of craftsman style carriage doors for my house and decided to use mortise and tenon joints. I hadn't made this kind of joint before so I asked my friend, Gary Katz, how to go about cutting the deep mortises. He suggested using a lock mortising machine, a tool designed for cutting mortise locks into doors.

The only companies I know of that make these tools are Porter-Cable and Virutex. I managed to find a used Virutex FC16s for $350 on eBay. It was missing some parts but was still functional. Like the Porter-Cable machine, it consists of a router that slides on a frame that clamps to the edge of a door – or as in my case, the pieces I wanted to mortise. The tool is controlled by crank-operated gears and an articulated arm. Turning the crank causes the router to slide back and forth along the frame and plunge slightly deeper with each rotation.

Proprietary mortising bits (5/8- to 1 1/4-inch in diameter) thread onto the end of the router's shaft. The width of the mortise will match the diameter of the bit; depth and length are set by the user – by adjusting the scales on the side of the machine

When the machine arrived I set it up and made a few test cuts – and was blown away how quickly and accurately it cut. Once I had gotten the hang of it I used the machine to cut mortises for the rail tenons on the carriage doors. I don't know that I'll ever use it to mortise in locks – but if I needed to I could.

Lock mortisers have traditionally been used on doors that are already hung or are standing vertically. The machine clamps to the edge of the door and cuts in from the side. The Virutex machine has a hydraulic lift to retract the router at the end of the cut – so it's as easy to cut from above as it is from the side (a plus when you are using it on something other than doors). I like that the tool has a dust collection port; by my estimate you can capture better than 75% of the chips and nearly all of the fine dust.

A lock mortise is a highly specialized piece of equipment. It's only worth owning one if you install a lot of mortise locks or need to cut mortises that are beyond the capacity of a plunge router or Festool Domino, and do not want to use a bench top mortising machine.

FC16s Specifications

Motor: 1,100 W -- 1.5 HP
Bit diameters: 5/8 to 1 1/4 inches in 1/8-inch increments
Max depth of mortise: 5 inches
Max length of mortise: 7 inches plus diameter of bit
Price: $1,350

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Jesse Wright is a finish carpenter and architectural woodworker for Architectural Molding in Concord, Calif. He learned the trade from his father and has spent the last few years studying historical architectural details and design.

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