In general terms, the word tolerance is used to identify the stated limit of acceptable deviation from a nominal dimension called out on a drawing. It is the allowable or “tolerable” difference from the nominal or ideal value that corresponds to the part. The use of tolerances helps to ensure that the final product is suitable for its end use, especially if the part is going into a larger assembly or must mate up with another piece.
Tolerances can range from microns, fractions of millimeters, to a quarter inch. It all depends on the industry and the scale of the project, as well as the material being used and the way the parts are designed. Anything inside the specified tolerance is considered acceptable, and helps to determine a good part, whereas anything outside of this range is considered a bad part and cannot be used.
This measurement is typically determined during the design phase by a company’s engineering and product development groups. Before an engineering print is finalized and signed off on, numerous tests are done to determine allowable deviations. Known as tolerance stacking, these tests help to ensure that the numbers are accurate.
Within the world of tube fabrication, tolerances are specified to accommodate differences or unique characteristics in raw materials and quality as well as other factors such as the equipment being used, the machine operator or the setup parameters.
Tolerances may impact how a tube bending project is quoted. For example, if a tight tolerance is required, cost may increase, due to the time required to achieve the desired range. If tolerances need to be amended to control costs, which is known as an allowance, or intentional deviation from the nominal dimension and tolerance, this approval is requested from the originator and documented.
If no tolerance is specified, the manufacturer will still try to stay close to the nominal value but there will normally be slight of deviation due to the reasons mentioned earlier. However, there should still be a tolerance established by the supplier to control production quality, and to ensure that manufacturing parameters can be set to meet the requirements for the part.
Find out about more about tolerances here.
This blog was authored by Marshall Arndt, Manufacturing Engineer, Sharpe Products.