Patent GB-701648-A (GB)
Title: Improved means for testing the roughness of surfaces
Inventor: WARING WALTER HAMILTON
IPC: G01B5/28
Filed: 1951-04-14
Abstract: 701,648. Gauging surface-roughness. NATIONAL RESEARCH DEVELOPMENT CORPORATION. July 10, 1952 [April 14, 1951], No. 8741/51. Class 106 (2) A gauge for comparing the surface-roughness of a sample surface with that of a specimen surface comprises a member 6 for engaging and moving along a sample surface either by rolling or sliding according to whether an opposed side in engagement with the specimen surface 4a slides relative thereto or not, thus indicating which surface is rougher. As shown, Fig. 2, a structure 1 has a knurled handle 2 held on a reduced end part 1a by a screw 21 and a block 3 rotatably mounted on the other end, being in screw threaded engagement with another reduced part. The block 3 has a hexagonal portion 4 with flat facets 4a finished with predetermined and different surface roughness varying from 4 to 130 micro inches arranged consecutively and indicated by numbers stamped on a flange 5. The block 3 may be rotated to bring any selected facet 4a adjacent a wheel 6 where the block is located by means of a detent 15 secured to a spring 16 anchored to the structure 1 by a screw 18 the detent 15 engaging internal splines 14 formed in the block 3. The wheel 6 is mounted in bearings in the forked end 7a of an arm 7 pivoted on a pin 8 between limbs 9 depending from a sleeve 10 slidable on the structure 1 and locked by a screw 11. The wheel 6 has a metal hub 6a locating two sets of four ball bearings 6b engaged on each side by needle-like supports 19 releasably held in the forked ends 7a by set screws 20. A stop 22 prevents excessive movement of the arm 7. The V- shaped outer portion 6c of the wheel 6 is made of a compliant material of very fine texture having as low as possible a coefficient of friction on the material under test in a dry state. A number of wheels of different materials may be provided for testing surfaces of different materials. The material may comprise natural or synthetic rubber of various grades or a plastic such as polyvinyl chloride or polytetrafluoroethylene. In use, the gauge is drawn across the sample surface with the selected facet 4a engaging the wheel 6 and parallel to the surface under test and the process is repeated using different facets 4a until one is found whose roughness approximates to that of the sample. If the specimen surface is smoother than the sample the wheel will slip at its contact with the specimen and roll over the sample ; if the specimen is the rougher the wheel will lock and so slide over the sample; if the roughness is approximately equal, the wheel may rotate draggingly sliding over both surfaces. By these means the roughness of the sample may be determined as lying between the known roughness of two specimens. For accuracy only surfaces of the same material similarly machined should be compared so that a set of blocks 3 may be needed e.g. twelve, four each of steel, brass and aluminium, each with surfaces finished by a different machining operation. To facilitate observation of any rotation of the wheel 6 it may be painted in halves of contrasting colour. Alternatively, the movement may be transmitted by gearing to an indicator. To assist in keeping the specimen and sample surfaces parallel to one another, one or more additional wheels may be mounted on the structure.