By W. A. Dubovick,


Engineered Precision Casting Company


Industrial investment castings, first produced in quantity during World War II, unfortunately were over-sold to designers. A combination of well-mean- ing but poor1y-informed salesmen and editors of trade publications were just a little too eager to tell the world about the glamorous and amazing "Lost- Wax Process." They failed to distinguish between the theoretically possible and the realistically prac- tical. When designers and production men found they weren't getting the tolerance of plus or minus .001 or .002 they were told to expect, the disappoint- ment retarded the greater use of the investment process in pioneer plants by five to ten years.


Since the Frustrating Forties, however, the invest- ment process has confirmed some of the original claims. General tolerances of plus or minus .001 may still be a dream, but smooth, dependable and con- sistent products with close dimensional tolerances when compared with sand castings are now a fact.


The investment process has come a long way and today's reliability can be chalked up to three factors:


(1) equipment and materials have been improved, (2) LC.L's publication of "How To Design & Buy Investment Castings" has influenced standardiza- tion of design tolerances, and (3) users have gained practical experience and have transferred it to their drawing boards.


Present industry practice indicates that investment castings can be designed to meet a tolerance of plus or minus .010 on dimensions up to 2 inches and plus or minus .015 on dimensions over 2 inches. What the upper size limit may be for the plus or minus .015 tolerance varies from one company to another, but this should be resolved when the new LC.I. hand- book is issued.


Unfortunately, many parts produced within these tolerances can not be used without secondary oper- ations. But it is recognized that in special instances and for particular needs much closer tolerances can be achieved. The following examples will show you some specific cases where investment casting dollars produced maximum results.


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