Patent GB-782016-A (GB)
Title: Improvements in or relating to linear dimension checking or measuring apparatus
Inventor: BARTLETT CHRISTOPHER LESLIE
IPC: G01B5/20
Filed: 1954-02-23
Abstract: 782,016. Linear-dimension gauges. BRISTOL AERO-ENGINES, Ltd. Feb. 23, 1955 [Feb. 23, 1954], No. 5349/54. Class 106 (2). An apparatus for checking and measuring the dimensions of a series of grooves, e.g. those of the fir-tree root of a turbine blade 4, in which the pitch between two adjacent grooves remains constant over the length of the grooves but is not necessarily the same pitch as that between any other two adjacent grooves comprises gauging pillars 11, 13 journalled with rotational and axial freedom in a holding member 15, abutments means 8, 9 for locating the blade in a reference position with the line of pitch measurement of the grooves parallel to the direction of axial freedom of the gauging pillar, and a cam-like projection 16 on the gauging pillar adapted to engage at least one flank of a groove and operate a dial gauge 19. The holding member 15 is so located in relation to the abutment means 8, 9 that the projection 16 may be made to engage a flank of a groove by turning the gauging pillar. In the embodiment of Fig. 1 a turbine blade 4 is held by a fixed abutment 5, Fig. 3, which enters the groove nearest the working portion of the blade, an abutment 6, hinged at 7 to permit slight movement, and entering the groove farthest from the working portion and a C-shaped clamp 8. The clamp 8 draws the blade against the abutments 5, 6 by tightening a screw 9 against a surface 10. The cylindrical holding member 15 can rotate about its axis on a platform 1 and carries one gauging pillar, e.g. 11, 13, for each groove in the blade, four in this case, and a pin 23 which can be inserted into any one of four holes 25 to locate the appropriate pillar in the gauging position. A circular flange 16 eccentric with respect to the pillar is provided at the lower end of each pillar which is adjustable vertically against a spring 18 to engage the flange in a groove corresponding to the length of the pillar, this engagement being effected by turning the knob 16a attached to the pillar until the flange 16 makes contact with the flank of the groove. In the gauging position the feeler of the dial gauge 19 contacts the top of the pillar. The gauge is adjusted to read zero for a perfectly positioned flank, and as the lengths of the pillars differ by an amount equal to the theoretical pitch of the grooves any deviation from zero of the gauge 19 indicates an error in a flank. After each measurement the pin 23 is removed, the member 15 rotated and the pin 23 replaced to locate the next pillar in the gauging position to gauge the next groove. In another embodiment, Fig. 4, a single flange 89 is carried on a gauging pillar 88 which is spring urged upwardly, and is brought into engagement with a groove by turning the pillar 88 by means of a handle 92 which also operates locking means for a pivoted segment 53. A series of gauging pins 66, each having a length such that its movement into the operative position brings the flange 89 opposite a corresponding groove, are carried by the segment 53 and held therein by screws for limited vertical movement. After a measurement has been taken the handle 92 is turned, releasing the locking device for the segment 53 and taking the flange 89 out of engagement with the root of the blade 101. The gauging pin 66 which is between the feeler 48 of the dial gauge and the top of the pillar 88 is replaced by another pin 66 by turning the segment 53, the handle 92 then being turned to lock the segment in position and register the flange 89 with a groove. The first of such operations is performed with the longest gauging pin in position and the dial gauge is then zeroized. The readings thereafter for the subsequent gauging pins gives the error in pitch relative to the first groove. Other embodiments of the invention are described in one of which a single gauging pillar carrying several cam-like flanges is employed. The flange members may engage one or both flanks of a groove or may engage the ridge between the grooves. Other forms of the abutment means are described in which the axis of the blade under test may not be vertical.