Drill Jigs Principles of Design Machinery ... - Evenfall Studios

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MACHINERY'S REFERENCE SERIES EACH NUMBER IS ONE UNIT IN A COMPLETE LIBRARY OF MACHINE DESIGN AND SHOP PRACTICE REVISED AND REPUBLISHED FROM MACHINERY NUMBER 3 DRILL JIGS THIRD EDITION CONTENTS Elementary Principles of Drill Jigs, by E, R. MARKHAM 3 Drilling Jig Plates, by J. R. GORDON - 21 Examples of Drill Jigs - 27 Dimensions of Standard Jig Bushings - - - - 50 Using Jigs to Best Advantage, by B. P. FORTIN and J. F. MIRRIELEES 53 Copyright, 1913, The Industrial Press, Publishers of MACHINERY. 49-55 Lafayette Street, New York City
CHAPTER I ELEMENTARY PRINCIPLES OP DRILL JIGS* The reasons for the use of jigs may be summed up under three heads, the order in which they are stated representing fairly well the fre- quency of occurrence, though not necessarily the importance, of these reasons: First, reduction of cost; second, duplication; third, accu- racy. Let us first consider the question of cost. As no article can, as a rule, be sold in open competition with similar articles unless its cost is somewhat proportionate to the quality of its competitors, commer- cial considerations demand that the cost be kept as low as possible, while the quality be kept as high as possible; and jigs are one of the chief agents of this in metal work. When a jig is considered, the first thing to be settled is whether it can be made to pay, and if so, how much. The answer to this often involves very many other questions, but can generally, if not always, be resolved into computations based upon the number of pieces to be made, and the probable cost of labor per piece when made with and without a jig, and the cost of the jig, including maintenance. Also the fact that often a much less valuable machine, or one less busy, can be used with the jig, may be an important consideration. If no other factor than cost of production is Involved, and it is found that the total cost of the jigged work will come very near that of the lot of articles when made without a jig, and no further order is in sight, it is pretty safe to abandon the jig idea; for it is apt to partake very much of the nature of an experi- ment, and the odds should be decidedly favorable to warrant the risk. The second reason the duplication of pieces has a somewhat dif- ferent foundation though cost enters here also, as will be seen later. Suppose the part to be made is subject to wear or breakage, as in agricultural and textile machinery, guns, bicycles, etc. We know, for instance, the strong disinclination anyone has for buying a wheel, the makers of which have gone out of business. It is at once recognized that repair parts cannot be bought from stock dealers, but must be made at excessive cost and delay. So we have before us the importance to manufacturers that the buying public shall have confidence in the interchangeability of parts in order that sales may be made at all upon the open market. It is a fact that where this reason holds good, there is also the reason that costs will be lessened, because production of large numbers of parts is taken for granted. And in considering whether or not a jig shall be made, this combination of reasons militates strongly for the jig. There is also another equally important reason for jigs, based on costs and interchangeability it is that, in MACHINERY, October, 1902 ; November, 1906 ; December, 1906, and January, 1907. 347514
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CHAPTER V USING JIGS TO BEST ADVANT
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USING JIGS TO BEST ADVANTAGE 55 be
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No. 1. Screw Threads. United States
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