657,588. Grinding. WYLDE, C. D., and KEATING, Ltd., T. May 12, 1949, No. 12719. Class 60] [Also in Groups XIX and XX] Apparatus tor comparing the contour of machine cut parts during the operation of tooling with a master template comprises an optical system with two beams of light which are arranged to converge to each other to embrace the fields of the master template and the workpiece respectively and to be conjointly retlected through a prismatic device to produce coincident outlines upon a common eye-piece, the optical system forming part of a machine tool whereby the contour of the workpiece can be continuously or discontinuously compared with the master tamplate and when necessary the edge accuracy of the tool held on the eye-piece. The optical system consists of a microscope with an adjustable eye-piece 1, Fig. 1, two prisms 5, 6, the engaging surfaces of which are half-silvered, a fixed objective 7 and an objective 10 provided with an image-reversing prism 8, the latter objective being in screw-threaded engagement with a sleeve 9 rotatably mounted in the microscope casing and adapted to be locked by a screw 30 so that focussing and angular adjustment of the image can be effected. The images may be projected on to a translucent screen 60 provided with crosswires to ensure that the images are compared at the centre of the screen, distortion due to residual errors in the optical system thereby being avoided. The microscope is secured to a block 12 which is provided with an aperture to receive the objective 10 and slidably mounted on two pillars 12a, 28 for vertical adjustment by means of a gut thread or the like 14 secured at its ends to the top of a splined rod 13 and a rotatable barrel 15 provided with a control knob. The splined rod is slidably engaged by a key in the block 12 and is provided with a screw 18 to effect fine adjustment of height. The mounting of the block 12 on the pillar 28 consists of a pad and a spring- loaded roller (not shown) and is provided with a felt wiper pad 44, while dust-excluding packings are provided on the mounting for the pillar 12a. Both pillars are secured to a table 24 which is displaceably mounted by antifriction bearings on a base 46 and provided with a slidable rod 52 having a spring-loaded screw adjustment 58. After the table has been displaced to the approximate position required, fine adjustment is obtained by locking the rod 52 with a screw 55 and rotating the screw adjustment 58. The pattern or master template which may be in the form of a master die 100, Figs. 5 and 6, is clamped by a bar 102 to a window plate 93 vertically adjustable on a second window plate 74 which is horizontally adjustable in a slotted block 71 and adapted to be clamped thereto by fly nuts 76. Each of these nuts is provided with a spring-loaded washer to ensure that the plate 74 is held in its position of horizontal adjustment until the fly nuts are tightened. A block 81 secured to the plate 74 has two lugs 86 carrying two screws 87 provided with locking screws 88 and a lug 82 carrying a screw 84. The latter bears against a lug 91 on a slidable block 90 while the screws 87 bear against two equally inclined surfaces 92 also forming part of the block 90 so that the plate 74 can be tilted by adjustment of one of the screws 87 and raised or lowered by adjustment of the screw 84 which is held in contact with the block by a spring 85. The workpiece 172, Fig. 9, which is illustrated as a punch, is supported between adjustable centres 173, 174 and is adjusted angularly about these centres by two screw jacks 186. The centres are carried on a table 123 transversely adjustable on a platform 122, this adjustment being effected by a rod 165 arranged to operate in the same manner as the rod 52. The platform 122 is hinged at 127 and is provided with a pin 133 which normally rests on the upper surface of a stepped bar 142. When this bar is manually displaced, the pin drops to the lower surface of the bar to impart a slight inclination to the platform 122 thereby enabling the workpiece to be backed off. This inclination of the workpiece also allows the grinding wheel profile to be compared with the pattern. If trueing is necessary, the machine table is moved to bring a diamond-tipped tool 208 into operative relation with the grinding wheel. The tool 208 is adjustably secured in a sleeve 209 in screw-threaded engagement with a carrier 212 mounted by spring-loaded tapered rollers on a guideway 207 shaped to provide the required profile and adjustably secured to the base of the work holder. The pattern and workpiece holders are set up on the table of a machine tool, such as a surface-grinder, by means of gauges. Comparison of the images is facilitated by the use of red light to illuminate the pattern and green light to illuminate the workpiece, since where the profiles exactly meet, a sharp definition of the two colours is observed, the clearance and interference areas appearing white and black, respectively.