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Tools for the Workshop

Tools for the Workshop A Monthly Selection of Recent Equipment and New Methods The Marlco Thread-Measuring Parallels It is a recognized criterion that the effective diameter of a screw thread is the most important dimension, which has to be kept within certain speci­ fied limits according to the class of work. This, however, presents its own particular problems, some of which arc enumerated below. Until now the most accurate method of positively checking the effective diameter has undoubtedly been the three-wire method. Unfortunately, however, for this an expensive measuring instrument, together Sieray Fluorescent Lighting with an expensive set of "best-size wires" have been Sieray fluorescent tubular lamps are at present made required, and the process of checking has been cum­ in two colours, "daylight" and "warm-white", the bersome. Optical means arc sometimes employed in output of both lamps being identical. The "daylight" inspection and other departments, but their price and lamp is claimed to be so good an approximation in their inability to withstand machine-shop vibrations colour to natural light, that it is possible to augment limit their usefulness. Screw thread micrometers arc light from windows with this type of lamp without often employed to measure the effective diameter, in any confusing two-colour shadows appearing. The which case to measure, for instance ⅝ in. bolt size and "warm-white" lamp is often preferred in canteens, everything intermediate up to the 6 in. B.S.P. size, a restaurants, staff-rooms, etc., because of its warmer number of micrometers would be required which colour. would naturally be expensive. Furthermore, they do A typical office scheme was designed recently for a not retain their initial accuracy for long, owing to their large accounts section in which the ceiling height was not uniform. It was desired to obtain the best lighting period. They arc guaranteed to determine the effective effect possible, while at the same time to disguise the diameter within 0·0002 in., and N.P.L. certificates can variations in ceiling height. The accompanying photo­ be supplied to this effect. At the same time their graph (FIG. 5) shows how the problem was overcome. application is simple, as dimension X has merely to A uniform mounting was adopted for all the fittings, be subtracted from dimension Y, as shown in FIG. 1, so that over a large part of the office the fittings were which gives directly the required dimension. suspended on about 20 in. of jack chain. In the parts By this method the man in the shop has not to rely where the ceiling was low, the fittings were mounted —as in the case of limit gauges—upon his personal straight on to the ceiling plates. In order to facilitate judgment, but can definitely see at a glance how much maintenance the fittings were connected by flexible material has to be removed so that the machined part leads with plugs and sockets on to the fittings. Thus comes within the limits called for by the specification. the whole fitting may easily be lowered for cleaning In order to simplify the process of measuring, an and maintenance. The lighting intensity is 12-15 fcs., clastic strand is used to form a linkage', as illustrated and Sieray 80-watt "daylight" fluorescent tubular in FIGS. 2 and 3. It will also be observed that this lamps are used. The scheme was planned by the arrangement will allow the checking of any effective Illuminating Engineering Department of Siemens diameter irrespective of size or sense of helix angle, Electric Lamps and Supplies Ltd., 38-39 Upper i.e. R.H. or L.H. threads of any diameter can be Thames Street, London, E.C.4, who supplied the fittings, lamps and control gear. small surface of contact. Limit gauges arc frequently used in inspection departments and machine-shops; however, the advent of quality control docs not now tolerate this method since these gauges do not indi­ cate the actual dimension. Ring gauges, of course, do not show any thread errors until the thread to be measured is under size and probably scrap. It is claimed that all the above defects have been overcome by the invention of the Marlco thread meas­ uring parallels. They were designed and made in col­ laboration with the National Physical Laboratory and embody the well-established principle of measur­ ing the effective diameter by means of a wedge and a vee, similarly to a screw thread micrometer, but instead of a linear measuring surface these parallels have a gauging surface of 0·5 in. and therefore retain their accuracy for a correspondingly longer measured with one pair of parallels of the appropriate range. Furthermore, this system of linkage will allow the measuring of components on the machine or between centres, as the clastic strands can be threaded into the slots of the parallels before or after they arc placed in contact with the work piece. In this con­ nexion it may be noted that the degree of accuracy obtained here depends mainly upon the precision of the gauge used to determine the size X and Y, and any suitable device such as micrometers, verniers, etc., can be employed. These gauges have been designed and grouped to form sets covering threadsof Whitworth, U.S. Stan­ dard, B.A. and metric forms, while "specials" can be made as required. FIG. 4 shows a set of Marlco measuring parallels in its plush-lined case, with a range of from 4½ T.P.I.— 40 T.P.I. Any of these parallels of any pitch or form can be supplied in single pairs or in sets, together with strand or suitable elastic. They arc manufactured by W. H. Marley and Co. Ltd., New Southgate Works, 105 High Road, London, N.11, and can be obtained from any merchant. 178 Aircraft Engineering http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Aircraft Engineering and Aerospace Technology Emerald Publishing

Tools for the Workshop

Aircraft Engineering and Aerospace Technology , Volume 18 (5): 1 – May 1, 1946

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Publisher
Emerald Publishing
Copyright
Copyright © Emerald Group Publishing Limited
ISSN
0002-2667
DOI
10.1108/eb031374
Publisher site
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Abstract

A Monthly Selection of Recent Equipment and New Methods The Marlco Thread-Measuring Parallels It is a recognized criterion that the effective diameter of a screw thread is the most important dimension, which has to be kept within certain speci­ fied limits according to the class of work. This, however, presents its own particular problems, some of which arc enumerated below. Until now the most accurate method of positively checking the effective diameter has undoubtedly been the three-wire method. Unfortunately, however, for this an expensive measuring instrument, together Sieray Fluorescent Lighting with an expensive set of "best-size wires" have been Sieray fluorescent tubular lamps are at present made required, and the process of checking has been cum­ in two colours, "daylight" and "warm-white", the bersome. Optical means arc sometimes employed in output of both lamps being identical. The "daylight" inspection and other departments, but their price and lamp is claimed to be so good an approximation in their inability to withstand machine-shop vibrations colour to natural light, that it is possible to augment limit their usefulness. Screw thread micrometers arc light from windows with this type of lamp without often employed to measure the effective diameter, in any confusing two-colour shadows appearing. The which case to measure, for instance ⅝ in. bolt size and "warm-white" lamp is often preferred in canteens, everything intermediate up to the 6 in. B.S.P. size, a restaurants, staff-rooms, etc., because of its warmer number of micrometers would be required which colour. would naturally be expensive. Furthermore, they do A typical office scheme was designed recently for a not retain their initial accuracy for long, owing to their large accounts section in which the ceiling height was not uniform. It was desired to obtain the best lighting period. They arc guaranteed to determine the effective effect possible, while at the same time to disguise the diameter within 0·0002 in., and N.P.L. certificates can variations in ceiling height. The accompanying photo­ be supplied to this effect. At the same time their graph (FIG. 5) shows how the problem was overcome. application is simple, as dimension X has merely to A uniform mounting was adopted for all the fittings, be subtracted from dimension Y, as shown in FIG. 1, so that over a large part of the office the fittings were which gives directly the required dimension. suspended on about 20 in. of jack chain. In the parts By this method the man in the shop has not to rely where the ceiling was low, the fittings were mounted —as in the case of limit gauges—upon his personal straight on to the ceiling plates. In order to facilitate judgment, but can definitely see at a glance how much maintenance the fittings were connected by flexible material has to be removed so that the machined part leads with plugs and sockets on to the fittings. Thus comes within the limits called for by the specification. the whole fitting may easily be lowered for cleaning In order to simplify the process of measuring, an and maintenance. The lighting intensity is 12-15 fcs., clastic strand is used to form a linkage', as illustrated and Sieray 80-watt "daylight" fluorescent tubular in FIGS. 2 and 3. It will also be observed that this lamps are used. The scheme was planned by the arrangement will allow the checking of any effective Illuminating Engineering Department of Siemens diameter irrespective of size or sense of helix angle, Electric Lamps and Supplies Ltd., 38-39 Upper i.e. R.H. or L.H. threads of any diameter can be Thames Street, London, E.C.4, who supplied the fittings, lamps and control gear. small surface of contact. Limit gauges arc frequently used in inspection departments and machine-shops; however, the advent of quality control docs not now tolerate this method since these gauges do not indi­ cate the actual dimension. Ring gauges, of course, do not show any thread errors until the thread to be measured is under size and probably scrap. It is claimed that all the above defects have been overcome by the invention of the Marlco thread meas­ uring parallels. They were designed and made in col­ laboration with the National Physical Laboratory and embody the well-established principle of measur­ ing the effective diameter by means of a wedge and a vee, similarly to a screw thread micrometer, but instead of a linear measuring surface these parallels have a gauging surface of 0·5 in. and therefore retain their accuracy for a correspondingly longer measured with one pair of parallels of the appropriate range. Furthermore, this system of linkage will allow the measuring of components on the machine or between centres, as the clastic strands can be threaded into the slots of the parallels before or after they arc placed in contact with the work piece. In this con­ nexion it may be noted that the degree of accuracy obtained here depends mainly upon the precision of the gauge used to determine the size X and Y, and any suitable device such as micrometers, verniers, etc., can be employed. These gauges have been designed and grouped to form sets covering threadsof Whitworth, U.S. Stan­ dard, B.A. and metric forms, while "specials" can be made as required. FIG. 4 shows a set of Marlco measuring parallels in its plush-lined case, with a range of from 4½ T.P.I.— 40 T.P.I. Any of these parallels of any pitch or form can be supplied in single pairs or in sets, together with strand or suitable elastic. They arc manufactured by W. H. Marley and Co. Ltd., New Southgate Works, 105 High Road, London, N.11, and can be obtained from any merchant. 178 Aircraft Engineering

Journal

Aircraft Engineering and Aerospace TechnologyEmerald Publishing

Published: May 1, 1946

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