Machining Tolerances Explained for Better Part Accuracy
Machined parts are not always produced at one exact dimension. Small variations naturally occur during machining, so drawings specify an acceptable range for each feature. This range is known as a machining tolerance. Knowing how tolerances work helps machinists understand part requirements, choose suitable machining processes, and avoid making a tolerance tighter than the application actually needs. What Is a Machining Tolerance? A machining tolerance is the permitted variation from a specified dimension. Instead of requiring a part to measure one exact size, the drawing gives an acceptable upper and lower limit. For example, a dimension of 1.00 ± 0.05 in allows the finished feature to measure anywhere from 0.95 to 1.05 in. The smaller the allowed variation, the more carefully the machining process needs to be controlled. Common Types of Machining Tolerances Machining tolerances can be specified in several ways. The most common types include bilateral, unilateral, limit, and geo...