This means that most of the data (or in this case tolerances) will be within 3 standard deviations of the mean. Further, placing a tolerance on this callout would cause it to be over dimensioned, and thus the reference dimension “REF” must be left to take the tolerance’s place.įigure 2: Tolerance Stacking: Normal distributionīefore starting a statistical tolerance analysis, you must calculate or choose a tolerance distribution factor. 004”, but is oftentimes miscalculated during part dimensioning. In this case, the tolerance window for the cutter diameter would be +/. ![]() For example, a corner radius end mill with a right and left corner radii might have a tolerance of +/. When an upper and lower tolerance is labeled on every feature of a part, over-dimensioning can become a problem. ![]() The cost of high quality tool holders and tooling with tighter tolerances can also be an added expense.Īdditionally, unnecessarily small tolerances will lead to longer manufacturing times, as more work goes in to ensure that the part meets strict criteria during machining, and after machining in the inspection process. ![]() This higher cost is often due to the increased amount of scrapped parts that can occur when dimensions are found to be out of tolerance. Tips for Successful Tolerance Stacking Avoid Using Tolerances That are Unnecessarily SmallĪs stated above, tighter tolerances lead to a higher manufacturing cost as the part is more difficult to make.
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