When building parts that come together, it's important to consider the gap distance between the parts, known as the tolerance. Tolerance is the amount of variation you allow in the design dimensions when the 3D model is fabricated. In other words, it’s the amount of ‘wiggle-room,’ or how accurate the model needs to be. It’s especially important to incorporate tolerance when designing parts that fit together (allowing adequate space between them). For example, with FDM 3D printed holes, it’s especially important to consider as each layer is compressed onto the layer below it, making it slightly wider than the thickness of the nozzle (by ~40-60%): 

Below are rough design guidelines for designing parts that fit together. They are the distance between the part and their associated fit (depending on printer/settings/layer height, etc.) with 0.4mm nozzles: 

  • <0.20mm - will be difficult to fit
  • 0.25mm - assemble once, leave it
  • 0.35mm - adjustable, but doesn’t move
  • 0.40mm - able to move slightly
  • 0.5-0.70mm - for movable and removable parts
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