Patent GB-1186701-A (GB)
Title: Indicators for Dimensional Gauges
Inventor: JOHNSON STANLEY GUSTAVE
IPC: G01B5/20
Filed: 1967-09-26
Abstract: 1,186,701. Screw thread gauges; indicating apparatus. JOHNSON GAGE CO. Sept. 26, 1967, No. 43700/67. Headings G1J and G1M. A pointer and indicator arrangement for a screw thread gauge comprises at least one indicator 18 or 25 with a dial scale, a pointer 21 and differential or tolerance pointer means comprising at least two pointers 30, 32 or 30a, 32a secured together in spaced relation on the dial. As shown two indicators 18, 25 are provided and the pairs of pointers 30, 32 and 30a, 32a are positioned on each indicator, these pointers being adjustable in position by a manually movable lever 28. Two thread gauges 10, 12 are mounted on a base 11, the gauge 10 having a fixed arm 13 supporting a gauging element 16 and a movable arm 14 supporting a gauging element 15. The gauging elements are adapted to engage a number of threads of a test screw S. The gauge 12 carries gauging elements 22-24 which are engageable with individual threads of the test screw and are spaced apart by 120 degrees. The indicators 18 and 25 have markings 19, 20 and 26, 27 respectively for setting the allowable pitch diameter tolerance of a test screw in the gauges 10 and 12 respectively. The pairs of pointers 30, 32 and 30a, 32a are mounted on the backs of the indicators and are coupled by a linkage 41 so that the positional adjustment of one pair of pointers by moving a lever 28 automatically adjusts the position of the other pair of pointers. A master screw is initially inserted in the gauge 12 and the dial of the indicator 25 is set so that its pointer 21 reads zero. The dial of the indicator 18 is similarly set with the master screw in the gauge 10. The tolerance markers 19, 20; 26, 27 are set to indicate the allowable pitch diameter tolerance and the pointers 30, 32; 30a, 32a are spaced apart by a given percentage for example 50 per cent of the tolerance allowable on the pitch diameter. The test screw is then inserted in the gauge 12 at different axial positions and is rejected if the indicator pointer 21 falls below the marker 27 for any position of the screw. The test screw is also rotated in the gauge 12, any movement of the pointer 21 being indicative of roundness errors in the screw. The test screw is then placed in the position where the reading of the pointer 21 was greatest and the pointer 30a is adjusted to coincide with this position, the pointer 30 automatically taking up the same position on the indicator 18. Any taper or out-of-roundness of the test screw greater than 50 per cent of the pitch diameter tolerance will be indicated by the pointer 21 moving out of the range between the position 30a and 32a. On placing the test screw in the gauge 10 and rotating the screw, the pointer 21 must remain between the tolerance markers 19, 20 as well as between the pointers 30, 32 for the screw to be acceptable. In a modification a single indicator such as 18 or 25 is used in conjunction with four sets of gauging elements and three tolerance pointers such as 30 to test screws for flank angle deviation, lead error, minor diameter deviation, pitch diameter deviation, &c.