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Description: | One of a set of 8 machine finish comparitor blocks in black mock-leather holder by Rubert & Co. Ltd. Scale no. 120 'Cylindrical Turning'. Yellow front with 8 turning comparitors. Full description on reverse including text "Cylindrical Turning produces similar profiles to Face Turning (Scale No. 119) and to shaping (Scale No. 125). All these methods use a single point cutting tool and the ratio of pitch to depth varies considerably. For this reason the accuracy obtainable by tactile comparison is less than that possible when assessing ground surfaces (scales No. 115 and 116). Nevertheless, turned surfaces up to 125 CLA can still be assessed with the finger nail to an accuracy of approxximately 50%. On rougher surfaces, however, finger nail assessment may not be reliable and visual comparison with the naked eye is also misleading because the eye registers the spacing but not the depth. It is therefore recommended that for surfaces rougher than 125 CLA a preliminary assessment be made using the finger nail and a final decision be taken by visual examination using a good magnifying glass (at least X8). The surface should be examined against a light source falling obliquely across the lay when the shadow thrown by the flanks will give a good comparitive indication of depth. Turned finishes better than 16 CLA can be obtained but not by common production methods, although soft metals (copper, aluminium, etc.) can be diamond turned (Scale No. 124) down to 1 CLA."
Acquisition source: Natural Philosophy Metrology Laboratory | License: | http://www.abdn.ac.uk/historic/Copyright_terms_conditions.shtml | Publisher: | ABDNP University of Aberdeen, Natural Philosophy Collection of Historical Scientific Instruments | Rights holder: | 47718 | Temporal: | 1960-1975 | Source: | University of Aberdeen | Creator: | Rubert & Co. Ltd. Precision Engineers | Identifier: | http://calms.abdn.ac.uk/Geology/dserve.e... | Go to resource |
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