The Serrated Bread Knife: Teeth That Cut Both Ways

"The object of the invention is to produce an improved and highly efficient cutting blade" and "the invention of this application relates specifically to the formation and relative disposition of the grooves ground at the edge of the tool to form these serrations so that the knife cuts easily and rapidly when moved in either longitudinal direction." "In practice I have found that by forming the knife as shown in Fig. 1, it cuts rapidly and easily when drawn in either direction and its efficiency for the purpose described is materially increased."

Clamp a plain kitchen knife edge-up in the vise with its blade protected by folded card. Mark five groups along the edge, each 2 cm long, with a 1 cm plain gap between groups. In the first group, file grooves 2 mm apart into the edge with a round needle file held tilted about 20° towards the handle. In the next group tilt the file the other way, towards the tip, and so on alternately. File only on one side, then take the burr off the flat side with a light stroke of the whetstone. Slice a crusty loaf with a plain knife, then with the toothed one, counting the strokes for each slice and weighing the crumbs each leaves on the board.

**Joseph E. Burns** of Syracuse, New York, filed US 1,388,547 on 25 September 1919; it was patented 23 August 1921. He suggested grinding each series at once with a rotary wheel carrying one ridge per groove, though he wrote that this was "not essential" to the invention. **Honest limits.** The notebook counts only where the edge touches; how deep the teeth are and how sharp their tips are matters too. Spacing and tip width are examples. Your stroke counts and crumb weights are the measurement.