# Accuracy, Precision & Tolerancing {% hint style="warning" %} The NExT Lab is working on better learning resources for you - this page is a work-in-progress article, so please check back soon! {% endhint %} Additional resources can be found [here](https://formlabs.com/blog/3d-printer-resolution-meaning/?utm_source=pinshape\&utm_medium=blog\&utm_campaign=resolution170824). ## Dimensional Accuracy 3D printing to dimensional accuracy can be tricky for a number of reasons. 1. The molten plastic shrinks as it cools to room temperature, guaranteeing dimensial accuracy is therefore hard to dial in. 2. Printers have a tendency to 'overshoot' slightly in corners as the printer head is forced to change direction. So corners have a tendency to be larger than they should be. If dimensional accuracy is important, you may have to adjust the size of the model being printed by incrementally changing the size, printing and measuring. ## Tolerancing FDM 3D Printing inherently prints slightly larger than when modelled using a computer. It is therefore important to account for this overprinting when designing parts that are intended to fit together. While it may be possible to sand the parts down to fit together accurately, this is often a lot of work and the fact that achieving this fit by sanding may actually wear through the shell of the print revealing the infill. Instead, to allow for this overprinting it is best to undersize the parts by a collective 0.5mm. For example if you are attempting to fit a round dowel-like shaped 3D printed part into a larger 3D print, reduce the diamater of the dowel by 0.25mm and increase the diameter of the hole in the larger print by 0.25mm; for a combined tolerance of 0.5mm. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://ms-kb.msd.unimelb.edu.au/next-lab/3d-printing/key-techniques/accuracy-precision-and-tolerancing.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.