Tolerancing: How can you make sure 3D printed parts fit together

You buy your first 3D Printer, set it up and get it extruding. You trawl online repositories like Cults3D and Thingiverse and browse through all the things you could print.

After a few months and many prints later, failed or otherwise – you’re bored. Sound familiar? You search for a modelling program you like, design an assembly and print it out – but it doesn’t fit.

Welcome to the wonderful world of tolerancing.

Printers aren’t perfect, and so parts may come out smaller or larger than designed in CAD. The degree to which a physical part can differ from its design size is known as its tolerance.

Tolerance can be referred to as tight, meaning parts with higher accuracy are needed, or loose, in which case some loss of accuracy is acceptable.

FDM 3D printers are accurate to 100 microns. That’s 0.1mm larger or smaller – which obviously doesn’t sound like much, but can mean a great deal depending on the application. A common mistake new designers make is making parts that fit into each other the same size, and not making one smaller than the other.

For some hobbyist projects, a difference of a fraction of a millimetre won’t matter. But in many manufacturing and engineering applications, the difference is critical. It may mean a screw no longer fits its housing, or two components don’t fit together as they ought.

Tolerances that you can print depend on how well tuned your 3D printer is.

For more information or to speak to one of our experts about your next project, call 01527 558 282 or fill out our contact form.