GP Drills


Boring Tools and their Makers

  Drill Jigs - Machinery's Reference Series, 1913    

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 frequency of occurrence, though not necessarily the importance, of these reasons: First, reduction of cost; second, duplication; third, accuracy.

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, commercial 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 experiment, and the odds should be decidedly favorable to warrant the risk.

The second reason the duplication of pieces has a somewhat different 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.

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