Small, or tight tolerances can increase cost in the manufacturing, inspection, and tooling of parts. The engineer or designer should strive to keep tolerances as large as possible while still maintaining the function of the part. However, just because you can hold tolerances smaller than a human hair doesn’t mean you need to. 005 inch are expected and achieved from today’s CNC mills. To provide some context, let’s consider an average human hair, which is around. In order to understand geometric tolerancing, it helps to think of parts as having varying degrees of imperfection. ![]() These variations (imperfections) are allowed within the tolerance limits (constraints) placed on the parts. When you look at machined parts, they look flat and straight, but if you were to precisely measure every single cross-section of the part, you would find that there are imperfections all over the parts. GD&T is an acronym for the geometrical product specifications – the ‘G’, the dimensioning – the ‘D’ and the tolerancing – the ‘T’. Tolerances are one part of GD&T, or Geometric Dimensioning and Tolerancing. It’s important to keep tolerances on engineering drawings in perspective, so I think of tolerances like bacteria-like bacteria, they’re not visible to the naked eye, but we know they’re there. Tolerances in engineering are an allowable amount of variation of a physical dimension. Tolerances are like Bacteria: Small, but Powerful If you want to go even more in-depth into this topic, check out our on-demand webinar on Conveying Design Intent with GD&T.
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