| 释义 |
ˈpoint angle
[f. point n.1 + angle n.2]
The angle at a vertex of a solid body; spec. (a) the angle between two diametrically opposite edges or surfaces at the tip of a tool; (b) the re-entrant solid angle at a vertex of an artificial cavity in a tooth.
1869Boutell Arms & Arm. iv. (1874) 67 The blade [of the Roman sword] was straight..and cut at an obtuse angle to form the point. In process of time this point-angle becomes more and more acute. 1908G. V. Black Operative Dentistry II. 9 All point angles are formed by the junction of three walls at a point, and are named by joining the names of the walls forming the angle. They are, therefore, named in three terms. Ibid., The point angles are formed where the line angles of one set meet the other set at the angle of the cavity. 1919G. W. Burley Machine & Fitting Shop Practice II. v. 142 The standard point-angle of lathe centres is 60° for small and medium-sized work-pieces. 1950P. Gates in A. W. Judge Machine Tools & Operations I. iv. 149 When drilling soft or ductile materials, drills ground with a smaller point angle tend to throw up considerable burrs on the back of the work. 1973W. W. Howard Rev. Operative Dentistry i. 9 Point angles are named for the line angles that form them. |