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July 2019  |  Craftsman’s Cribsheet #78

The straightness of cold finished steel bars, and all other barstock for our machines, is of critical importance. The controlling standard is ASTM A 108, Table A1.4. However, the standard errs in claiming the tolerances are measured by placing the bars on a level table and the depth of the arc then measured with a feeler gage and straight edge. While that will give a value for the maximum departure from straightness, it does not actually describe the true geometric relationship.