The object of Bevelling off the plugs in the Marconi tube is to enable the sensitiveness of the tube to be varied by turning it round, so that the small quantity of filings lie in between a wider or narrower part of the gap.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming
The principle is that Bevelling off the front edge of the cutter, as shown in Fig.
"Modern Machine-Shop Practice, Volumes I and II"
Joshua Rose
1417, for example, represents the ordinary form, the points being rounded; hence, when the legs are closed the point of contact between the inside and outside calipers will be at A, while when they are opened out to their fullest the points of contact will be at B. This may, however, be remedied to a great extent by Bevelling off the ends from the outside as shown in Fig.
"Modern Machine-Shop Practice, Volumes I and II"
Joshua Rose