The Crossed-Bar Knife Sharpener: Two Steels Make a V

"On the side of the handle A are attached two plates, B and C", "both pivoted to the handle by bolts or screws". "It will thus be seen that the two plates are pivoted in opposite edges, and that the projections or thumb-pieces a a and b b may be brought closer together or farther apart, as may be desired." "On the outer face of the inner plate, B, and on the inner face of the outer plate, C, is an inclined recess, in which the steel bars D D are inserted. Said recesses running in opposite directions, the bars cross each other, forming an angle in which to sharpen the knife." A lever E has a projection that, "when the lever is turned up in proper position", will "firmly lock the plates and steel bars together, while when the lever is turned down the plates are loosened, and the plates and bars may be adjusted as desired."

Clamp two round steel rods in the vise so they cross in a V, and set the angle between them with the protractor: start at 40 degrees. Hold a kitchen knife upright and draw it down and back through the V ten times with light pressure. Slice a sheet of paper held by one corner and note how cleanly it cuts. Open the V to 60 degrees and repeat on the same knife. Look at the edge under the loupe after each and compare with the notebook: which cut better, and which edge looked more robust?

**Septimus C. Stokes** of Manchester, New Hampshire, received US 102,727, dated 3 May 1870. His claims are the locking lever and the combination of handle, plates, bars and lever. **Honest limits.** That the edge takes the V's angle is an approximation: how the knife is held and the bars' shape change it. The patent does not state the angle; the angles and the 0.1 mm distance in the notebook are examples. Your paper test is the measurement.