Screw-Depth Portable Router: The Motor's Threaded Casing Screws Into a Split Base, One Turn per Sixteenth (Carter, 1924)

"In practice, the threads of the shell 3 and support 9 are preferably about one-sixteenth inch pitch, so that each revolution of the motor or support in either direction moves the tool A correspondingly."

Print the casing and the base in PETG. Clean the threads and screw the casing into the base by hand; it should turn smoothly all the way. If it is tight, run it in and out a few times. Check the base's bottom is flat by rubbing it on abrasive paper on a flat board.

Fit the collet adapter on the motor's shaft and tighten its set screws. Push the motor down into the casing so its face sits on the casing's bottom with the collet through the hole, and screw it in with its two M4 face screws. Solder the supply leads through a toggle switch, sleeve the joints, and lead the cable out through the casing's open top. Set the DC supply to the motor's rated voltage.

Fit a straight bit in the collet. Screw the casing into the base until the bit's end is level with the base's bottom on a flat board, then screw it in four more turns for a 1/4 inch (6.35 mm) deep cut. Put an M5 screw through the lugs with a wing nut and tighten it, closing the split on the thread.

Clamp a board down. Hold the router by its casing and wings, base flat on the board, switch on, and move it along a clamped straightedge so the bit cuts a groove. Take deep grooves in two or three passes, a few turns deeper each time.

**Ray L. Carter** of Syracuse, New York, US 1,514,894, dated 11 November 1924, filed 29 September 1923. He claimed a motor with a threaded casing, "a hollow cylinder having a split threaded portion adapted to engage the threaded portion of said casing whereby said tool may be moved relatively to the work", a plane bottom to move over the work, and means for locking. His motor ran on mains through a lamp socket at over 7,000 r.p.m.; ours is a small DC motor on a bench supply, a light-duty router. His casing was insulating material; ours is printed PETG. His fan and baffle disk are left out. The pitch is his; the other sizes are ours.