Hole Tolerance


The roundness of a cast hole is affected by the surrounding metal. If an uneven mass is adjacent, the hole will be pulled out of round. If the surrounding metal is symmetrical, holes up to %" diameter can be held to ± .003" when checked with a plug gage. Larger holes may be affected by interior shrinkage or pulling, and the foundry should be consulted.


The longer the hole or the more mass of the section around it, the more pronounced the o I ~1~1~ ' Figure 2 1 m I Figure 3 Tapered Holes


A. TAPERED WITHIN THEMSELVES. The notes above are applicable. We recommend that such holes be dimensioned at the lesser diameter and the angle given. The angle can be held to ± 1/ ::! 0


•


B. TAPERED WITH RESPECT TO ANOTHER FEATURE. Here again the notes on holes apply. The angle from any given position will vary ± 1°.


Curved Holes


Since curved holes are formed by either soluble wax or preformed ceramic cores, the normal tolerance tends to be doubled. A factor of 2 times must be applied to the tolerance on all dimensions controlling such a feature. Since such holes cannot be sized, a diameter tolerance of ± .005" per inch also applies.


effect. Figure 2, shows the effect of shrinkage concavity which will be present to some extent in all castings. The opening at the top and bottom of the hole will be approximately the same dimension while the center will be a larger diameter. Thru holes which require clearance and can be checked using a plug-type gage can be held to fairly close tolerances if the larger diameter in the center is ignored. If, however, the sidewalls of the hole are used as bearing surfaces, a simple reaming operation will size the cast opening. Figure 3, shows the effect of shrinkage on a hole diameter when a heavier section is to be in the proximity of the hole itself. It will be noted that the diameter is distorted due to the additional mass shrinkage of the heavier section. The figure shows a graphic illustration of the distortion which will be present to a greater or lesser degree in every casting with the heavier mass affecting the shrinkage. Greater shrinkage will occur at the point of larger mass and distort the shrinkage pattern of the hole.


Angular Holes


Since these holes are usually formed by metal cores within the die, the tolerance restrictions for curved holes do not apply and normal tolerance bands are usually acceptable. If the angle formed by the two centerlines is greater than 120°, the hole can be sized, but if it is less, a diameter tolerance of ± .005" per inch must be used.


Internal Radii, Fillets


These should always be given as wide tolerance as possible. They are difficult to control and can only be checked approximately by radius gages, or at a premium by an optical comparator.


9


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24