Rack-and-Pawl Plunge Router: The Motor Rides One Post on a Spring and Steps Down a Tooth at a Time (Carter, 1925)

"By this arrangement cavities of considerable depth may be routed by successive stages wherein each stage represents the normal depth the tool is designed to cut."

Cut 1 inch square steel tube 200 mm long. Saw and file a slot 8b 6 mm wide and 100 mm long down the middle of one wall, starting 40 mm from the top. Push the post into the base's socket and bolt it through with an M6 bolt and lock nut. Drop a compression spring 10 into the post, then a plunger 13: a block of flat bar that slides in the tube, tapped M6 on its back for the screw that runs in the slot, with an M6 rod 13' standing up from it. Screw a flat-bar cap 12 across the post's top with a hole for the rod, and run two gauge nuts 14, 14' onto the rod above it.

Print the holder and base. Lay a strip of flat bar in the guide's recess 15 as the gib plate 15' and run two M5 set screws 16 against it, one with a wing nut on its head to lock the holder by hand. Slide the guide down over the post and fix it to the plunger with an M6 screw through the slot. Set the screws so the holder slides freely without rattling. Screw the 1924 motor casing into the holder and lock it with an M5 screw and wing nut through the lugs.

File a pawl 18 from flat bar with a hook 18' at its top to catch the rack's teeth, and a locking pawl 20 with a tooth 20' at its top and its lower end bent out as a foot 20d. Pivot the locking pawl on the base's boss with an M5 screw, held against the rack by a spring-steel leaf 20b. Pivot one end of a lever 19 on the boss and the pawl's lower end to the lever partway along, with a second leaf 20c holding the pawl to the rack. Each press of the lever's handle pulls the holder down one tooth, and the locking pawl drops in under it.

Fit a straight bit. Set the gauge nuts so the plunger's rod stops on the cap at the depth wanted. Clamp a board, rest the base on it with the cutter clear, switch on, press the lever once and move the router across the area; press again and repeat, until the nuts stop it. Press the locking pawl's foot and the spring lifts the cutter out.

**Ray L. Carter** of Syracuse, New York, US 1,565,790, dated 15 December 1925, filed 21 March 1925, improving his US 1,514,894. He describes a holder "formed at one side with a guide portion having an angular vertical opening, for slidably mounting the holder upon a pedestal or post of substantially the same angularity", a coil spring housed in the pedestal, a ratchet rack and pawl to move the motor step by step, a locking pawl, gauge nuts, and a plate with set screws to take up wear. His post is triangular and cast; ours is 1 inch square steel tube. His holder and base are metal; ours are printed PETG. His motor ran on mains; ours is the small DC motor of our 1924 router. The sizes are ours.