- Standard Tolerances
Machinists use standard machining tolerances for the most widely fabricated parts. There are standard machining tolerances for parts such as threads, pins, pipes, and so on. Some milling services offer typical tolerances of +/-0.1mm. Machinists usually apply these tolerances when the customer doesn’t specify tolerance levels. These typical tolerances can be found on a CNC machining tolerance chart.
- Unilateral Tolerances
Unilateral tolerances accommodate deviations in only one direction. The deviation is either positive only or negative only. An example of such tolerance is +0.00/-0.06mm. This means that the finished part can be at most smaller by measurement of 0.06 mm but must not exceed the specified measurement. You usually implement unilateral tolerance when designing a part that goes into another. The part must not be bigger than the specified measurement as that will mean it will be unable to go into its position.
- Bilateral Tolerances
When you use bilateral tolerance, the deviation from the given dimension can be either negative or positive. This means it can be a tiny bit bigger or a tiny bit smaller. An example of a bilateral tolerance is +/- 0.06mm. This indicates that the machined part can be 0.06mm shorter or longer than the specified measurement. Bilateral tolerances are used mostly for exterior dimensions.
- Limit Tolerances
A limit tolerance is a type of CNC machining tolerance expressed as a range of values, where the part is fine as long as the measurement falls between that range. 13 – 13.5mm for example is a limit tolerance indicating that the part must have a measurement that falls between the upper and the lower limit. (13mm is the upper limit and 13.5mm is the lower limit)
- Geometric Dimensioning and Tolerancing
Geometric dimensioning and tolerancing are much more thorough than the other systems of machining tolerances. It is a type of CNC machining tolerance that highlights the measurements and allowable deviations. It also outlines specific geometric characteristics for the machined part such as how flat it should be, its concentricity, and its true position. Geometric dimensioning and tolerancing are often used for parts that have extremely precise dimensions.