Tolerance is a specification for how much variation from ideal measurements you can tolerate for your parts. You must specify a tolerance in menu Job | Settings. If you are new to thinking about small tolerance values, consider the thickness of some common items:
Note that metals allow for parts of tighter tolerance than plastics.
For specific tolerance limits please click here.
You can specify tolerances in three ways:
Vague Tolerances Vague tolerances are not accepted, such as, "The diameter must be exactly 1 inch." Or, "This dimension is critical." Or "Size must be accurate."
Often, mechanical drawings show lines with arrows and other symbols that indicate distances and other measurements that must be held to a certain tolerance. For
eMachineShop CAD offers the ability to rely mostly on implicit dimensioning which is easier and faster to use. Implicit dimensioning is supported via the general tolerance at Job | Settings | Specifications.
The linear tolerance value you specify at Job | Settings | Specification is referred to below as "T". In simple terms, the value you select for T is used approximately as follows:
In conformance with industry standard, design dimensions are after non-organic and mechanical finishes (anodize, electroplate, brush, grind, sand blast etc.) but before organic coatings (powder coat, etc.). Example: A 10 mm cube that was electroplated should measure 10 mm after electroplating.
Below is the complete definition of how default tolerance is used at eMachineShop, requiring an understanding of GD&T and ASME Y14.5. The following is used as the basis for determining whether your part conforms to your specification:
Additionally, tapped holes shall be perpendicular to the originating surface within +/- 2 degrees.
The general tolerance does not apply to
Following is the order of precedence of tolerances with
For parts made by extrusion the general tolerance applies to the cross-section.
Tolerances may not be met when impractical due to
Measurements are done at at 20C +/- 1 or 68F +/- 2.
* The value 1.4 (SQRT(2)) and 2.8 (2 * SQRT(2)) are derived from the GD&T equivalent of older style square zone tolerancing where +/- T is applied separately to each axis.