Call: 800.221.0419
Fax: 603.434.7880
(info@alcumet.com)

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AlCuMet Inc.
3 Planeview Drive
Londonderry, NH 03053

Toll Free: 800.221.0419
Call: 603.432.6220
Fax: 603.434.7880

Email: (info@alcumet.com)

Flatness (Dish)

Flatness and straightness are so closely related that confusion may arise unless the foundry and purchaser clarify the definitions before production.

Mil Std. 8 specifies "a flatness tolerance is the total deviation permitted from a plane and consists of the distance between two parallel planes between which the entire surface so tolerated must lie." In measuring, the parallel planes must be the minimum distance apart.

Flatness Tolerance

Degree of flatness in an investment casting is almost always determined by the volumetric shrinkage of wax and metal during cooling. Usually in the center of the mass, this shrinkage is called "dish" (shrinkage, dip, or "out of flat"). Dish can be controlled by specialized techniques, but it will always occur to some extent. General flatness tolerances cannot be quoted because they vary with configuration and alloy used. The following is a rough guide for areas under 6 square inches.

Degree or flatness

Allowable dishing is in addition to basic tolerance. Thus on a block 1" ±.005" thick, the following would apply:

Flatness Measurement

The method of measuring flatness should be specified by the purchaser. It may vary from a simple surface plate and feeler gage for normal tolerances to full layout with equalization and dial indicators for premium tolerances.

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