Resolution, Accuracy, and Tolerance – What’s the difference?

Tolerance, Accuracy & Resolution
 

              Far too often we have seen customers enquire about a 3D Printer’s resolution when they actually were trying to enquire about its accuracy and vice-versa!

            The problem is so grave that even some of the 3D Printing service providers fall prey to this conundrum and end up giving unsolicited answers. So we decided to write an article addressing the difference between these terminologies and what they signify.

Resolution:

 

          Resolution of a 3D Printer is the smallest detail of a part geometry that can be captured effectively. Different 3D Printing processes have different resolutions and they vary from machine to machine based on the process architecture and the hardware components used.

           The resolution of a 3D Printer in X-Y direction is invariably different from its resolution in the Z-direction. The X-Y resolution of the 3D Printer depends either on the nozzle diameter of the extruder or the spot diameter of the laser beam, based on the 3D Printing process chosen. Whereas the Z resolution of the 3D Printer depends on the layer thickness setting chosen for that particular build.

 

The left-most part has better Z-resolution than the right-most part. Image Source: all3dp

 

        Smaller the nozzle diameter/laser spot diameter, better the resolution in the X-Y direction and vice-versa. Similarly, lower the layer thickness setting value, better the resolution in Z-direction and vice-versa. Better resolution means that even the tiniest details can be captured effectively.

        Some of the 3D Printing processes can capture details as small as 0.4mm. But usually, such a minute feature detail is too fragile for a 3D Printed part and there is a chance that it may break off during part cleaning and post-processing. That’s why although the resolution of a 3D Printer may be 0.4mm, we still recommend that the minimum feature detail be at least 0.8-1 mm thick.

Accuracy:

 

             Accuracy is how close the dimensions of the manufactured part concur with the given 3D CAD design.

             For example, if the dimension of the 3D CAD design is, say, 2mm, and if the actual part dimension after manufacturing is 2.5mm, then the part is said to be less accurate than the part whose dimensions are, say, 2.2mm after manufacturing. Critical part assemblies require high dimensional accuracy for proper fitment and functionality.

Measuring the Dimensional Accuracy

Tolerances:

 

              Tolerances are subjective; they are defined by the designer and they vary based on the part’s application. A single part assembly can have varying tolerances at different places. Based on the part application, the designer may either opt for a clearance, interference, or a transition fit corresponding to which there will be tolerances specified. The designer may opt for tight tolerances if the part assembly is very critical, otherwise, he may opt for relaxed or loose tolerances.

 

Image Source: Formlabs

 

              If the Tolerance is tight, you need parts with higher dimensional accuracy, and if tolerances are loose, you can do away with less accurate 3D Printed parts.

              For example, given my part requirement, if I have specified the tolerances for my part geometry to be within (+/-) 0.1mm of the nominal CAD dimensions, then I cannot opt for a 3D Printing process like Fused Filament Fabrication (FFF) which offers dimensional accuracy in the range of (+/-) 0.5mm.

            Moreover, tighter the tolerance, higher will be the part cost because the 3D Printing process needs to be more refined to cater to such highly accurate parts. So unless absolutely necessary, giving tight part tolerances on the part geometries should be avoided.

 

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