The Cone-Roller Taper Gauge: A Pencil Line That Closes In as It Goes

"A, represents a bar which may be of rectangular form of any suitable length and having a rack at one side of it. The bar A, passes through a mortise in a square block or stock B, in which a conical roller C, is placed, the axis of the cone being parallel with the bar A, as shown clearly in Fig. 3." "The line h, may be made more or less taper by adjusting the bar c, and fence e, on the block or stock B. By this adjustment the conical roller C, may be made to bear upon the 'stuff' D, at any point on its periphery and the bar A, moved with a quicker or slower speed, according to the diameter of the portion of the roller C, that bears on the stuff".

**Stock.** Saw a stock 12 × 8 × 4 cm from hardwood block and screw a fence strip along one edge of its underside. **Cone.** Rasp and sand a cone 6 cm long, 10 mm across at the small end and 40 mm at the large, from hardwood block, and drill it through its axis. Glue it on 25 cm of M6 threaded rod and mount the rod in two holes through blocks screwed under the stock, so the cone's underside just touches the board and the rod runs parallel to the fence. **Pencil carriage.** Drill a small hardwood block to slide on a strip of hardwood glued under the stock, epoxy an M6 nut into it on the rod, and fix a pencil through it pointing down. As the cone rolls, the rod turns and the nut walks the pencil in. **Test.** Set the cone so its 20 mm section touches, hold the fence on a pine board's edge and push the gauge 1 m. Measure how far the line closed in with the ruler and compare with the notebook. Move the stock so the 40 mm section touches and do it again.

**John Marvin** of Bellport, Suffolk County, New York, received US 22,564, dated 11 January 1859. His stock carried a table graduated in feet and inches for setting the band and fence to the taper wanted, a spiral spring kept the stock from slipping on the bar, and he wrote that it "may be cheaply constructed at a cost not much exceeding the ordinary parallel gage." **Honest limits.** A cone on an M6 threaded rod with a nut-borne pencil stands in for Marvin's screw and rack; the kinematics, one pitch per turn, are the same, and no taper table is given. The notebook ignores slip; its pitches and diameters are examples. Your measured tapers are the result.