GB882075A - Device for checking accuracy of shape - Google Patents

Abstract

882,075. Gauging departure from standard form. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Sept. 4, 1958 [June 4, 1957], No. 17706/57. Class 106 (2). [Also in Group XL (b)] A method of testing the profile of a workpiece by comparing it with a standard profile consists in preparing a trace 15 by tracking the standard 12 by a feeler 10 and then tracking the workpiece (not shown) in this apparatus without producing a further trace so that deviation of the marking point 11 (or a mark representing this) from the trace represents disparity between the workpiece and the standard and inaccuracies of the apparatus cancel out. The standard 12 is fixed to a table 1 which is mounted for movements in two perpendicular directions on a base 7. The table is then moved by hand so that a fixed feeler 10 travels along the outline of the standard 12. A fixed scriber 11 meanwhile traces a path 15 on a transparent plate 14 which is smoked or otherwise coated, the path 15 being representative of the shape of the article 12. To test a workpiece, it is fixed to the table 1 in place of the standard 12 and the scriber 11 replaced by an eyepiece 19 carrying a cross-line graticule or a tolerance circle 21 the centre of which occupies the position previously occupied by the scriber 11. An alternative arrangement is shown in Fig. 7 in which an image 15a of the plate 14, still carried by the table 1 (not shown), is focused on a screen 22 having a tolerance circle 28 marked thereon. In addition to this, a mirror 27 may be semi-silvered so that part of the light passes on to a masking plate 29, provided with a hole 30 through which light passes on to a photoelectric cell 31. In this case, the response of the cell merely indicates whether the path 15 is within the required tolerance. If, however, the plate 14 is formed as in Fig. 9, the area to one side of the trace being blacked out, then the response of the cell would indicate deviations from standard in either direction. In other embodiments, the table 1 may be pivotally mounted, or the feeler 10 may be carried by the table 1, the body to be tested being fixed on the base 7. Means may also be provided for enabling the body 12 to be tested along other sections.