Angularity


Angular tolerance is dependent on the configuration forming the angle. Sketch "A" cannot be sized, but in certain cases after sufficient


data has been reviewed, the die can be reworked to bring the part closer to optimum. Sketches "B" and "C" can be reworked to ± 1h


0


and ± 1 ° respectively. Obviously, however this is dependent on the alloy and its condition.


. :··· :~;::;\.


Positioning


The tolerance on the position of holes and bosses · is dependent on the configuration of the parent casting. The position of holes or


bosses on the periphery of the examples shown under concentricity will obviously be affected by the degree of eccentricity shown. The position of holes or bosses on a flat plate will be controlled by the linear tolerances already given. A new factor enters here, however.


The linear tolerances are based on volumetric shrinkage, and holes and bosses disturb this shrinkage pattern. It is possible to reduce


these tolerance bands by about 10% when applying them to a configuration that disturbs the shrinkage pattern. It is difficult to predict the exact amount and the foundry may


wish to rework the tooling to take full advantage of these better tolerances.


Holes and bosses on a parent


diameter are affected by the degree of out of roundness exhibited by


the parent diameter although the notes above concerning the breakup of the shrinkage pattern are still valid.


As a rule of thumb, it may be said that a bolt circle diameter carrying


holes and bosses will have the same amount of out of roundness as any


other diameter. Thus a 2" BCD will be round within .025" TIR. This


is best expressed, and designed for, in terms of true position.


The parallelism and straightness of such holes is a function of the straightness of the parent casting and the tables already given will apply.


4 holes,


equispaced within .013" of t rue posit ion


2,000 Bolt Circle Diamet er Basic


8


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