Patent GB-667671-A (GB)
Title: Improvements in and relating to bore gauges
IPC: G01B5/08
Filed: 1948-12-06
Abstract: 667,671. Linear-dimension gauges. EXPRESS LIFT CO., Ltd., and REVELL, W. E. Jan. 6,1950 [Dec. 6, 1948], No. 31540/48. Class 106 (ii). A bore gauge has gauging curves or surfaces which are annules of a sphere of a diaameter equal to the bore diameter for which the gauge is designed. An annule is defined as the part of a hemi-sphere lying between first and second curves on its surface, the first curve not touching the great circle forming the boundary of the hemi-sphere and the second curve lying on the opposite side of the first curve to the great circle. The second curve may be coincident with the first or may be reduced to a point. The gauge may thus be used to detect lack of circularity in a bore and may also be partially introduced into the bore during the machining of the latter to indicate when the bore is approaching the correct size. In one form, Fig. 2, the annules are surfaces formed on disc-like heads 8, joined by a member 10. The latter may be formed in two parts which screw together with or without distancepieces and are then locked. The gauge may thus be adjusted for different diameters. If the member 10 is shortened, the inner circles 24 become the effective annules, while if it is extended, the outer circles 25 become the annules. In another form, Fig. 6, the gauge comprises a right circular cylinder 11, mounted on a handle 12 and having its circular ends bevelled to form annules of a sphere having its centre at the centre 14 of the cylinder. The gauge may be tilted to the extreme position shown in dotted lines before it ceases to fit the bore. The bevels may be formed as parts of spheres of smaller diameter than that of the bore, in which case the annules are circles on the bevels. In a simpler form (not shown) the ends of the cylinder are not bevelled, the annules being formed by the circular boundaries of the ends. In this case, the ends of the cylinder may be flat or parts of spheres of diameter equal to or greater than that of the bore. The annules may alternatively be formed on the end surfaces of a tube and parts of the tube may be cut away to avoid projections in the bore. In the manufacture of the above-mentioned gauges, the cylinder is mounted on dead-centres on its axis and ground to size. If the ends are to be flat, they are then ground and lapped but if they are to be spherical, they are turned by a tool mounted in a swinging saddle and then preferably form-ground and lapped. To produce a "Go and Not-Go " gauge, a right circular cylinder is first worked to provide at its ends circular annules of a sphere of a diameter equal to the " Not-Go " limit and the cylinder is then mounted on diametrically-opposed centres in its middle and cylindrically ground and lapped to the " Go  " limit. The gauge should thus be able to enter a hole with the centres coaxial with the hole but it should not be possible to rotate it about its axis through a right angle. The gauge may be formed from a bar of polygonal section, the ends being worked to provide a partspherical surface 26, Figs. 16a and 16b, which forms the gauging annule and the corners 27 being cut away and providing an increased lead for entering the bore. A square bar may have corners 32, Fig. 17b, worked to form annules of a " Not-Go " sphere and edges 30, 31 which lie on cylinders having axes perpendicular to one another and to that of the bar and of diameters equal to the " Go limit. Thus, the gauge should be able to enter the hole with its plane e-e containing the axis of the hole but should not be rotatable to a position in which its plane d-d includes the axis.