Ordering 3D printed parts to fit together mechanically requires planning and understanding tolerances. A well-balanced tolerance ensures the right fit - whether you need a loose fit or a permanent connection. In this article, we review why tolerances are important, how 3D printers typically cope with dimensional accuracy, and provide concrete guidelines for three common types of fits: slip fit, interference fit, and press fit.
Why are tolerances important?
Tolerance describes how large a deviation from a nominal dimension can be before the function is at risk. It is often expressed as x ± y, where x is the desired (nominal) measure and ± y In mechanics and mechanical engineering, correctly chosen tolerances are essential for components to fit and function as intended, without risking either excessive friction or loose fits.
In 3D printing, tolerances are affected by, among other things:
- Printer model and calibration
- Material properties (e.g. shrinkage during cooling)
- Geometry of the printed model
- Selection of layer height, speed and other print settings
Generally speaking, most professional 3D printers are around a tolerance of ±0.05 mm, but keep in mind that deviations can increase with larger detail size or complex geometry.
Three common types of pass
Glide Passage
- Definition of: The shaft always has a small clearance (gap) in relation to the hole, which allows it to move freely.
- Area of use: Used when parts need to be able to rotate or slide, for example in bearings or movable joints.
- Recommended dimensions for 3D printing:
- Tolerance: about 0.2 mm between moving parts.
- Example: If the shaft is 10 mm, the hole should be 10.4 mm to give plenty of clearance and reduce the risk of friction and binding.
Intermediate adjustment
- Definition of: The pass can give either a slight play or a slight pressing resistance when the shoulder is put in the hole.
- Area of use: Suitable for applications where you want to be able to assemble and disassemble but still have some stability, such as axle-wheel joints or parts that sometimes need to be disassembled.
- Recommended dimensions for 3D printing:
- Tolerance: approx. 0.1 mm between parts.
- Example: If the shaft is 10 mm, the hole should be 10.2 mm to create an easy fit where the part can be assembled by hand but still be relatively stable.
Press fit
- Definition of: The shaft is pressed into the hole with force, creating a permanent or very firm connection.
- Area of use: Ideal for high-strength applications, for example in press joints or guide pin joints where disassembly of the part is not expected.
- Recommended dimensions for 3D printing:
- Tolerance: approx. 0,05 mm between parts.
- Example: If the shaft is 10 mm, the hole should be 10.1 mm to ensure a proper press fit.
Tips for better 3D outcomes
- Calibrate the printer: Make sure your 3D printer is well calibrated. Small deviations in the X-, Y- and Z-axes can mean that a supposed tolerance of 0.05 mm is actually larger.
- Choose the right material: Different materials (e.g. PLA, PETG, ABS) behave differently during the cooling phase, which can lead to shrinkage or warping. Take this into account in the design.
- Feel free to try a test piece: Before running a larger print project, print a small test piece to verify that the fit and tolerances match your calculations.
- Post-processing: Sanding, drilling or other finishing may be required to achieve the desired fit, especially if the surface needs to be extra smooth.
Executive summary
Correct tolerance selection is crucial when ordering or designing mechanical parts for 3D printing. By understanding how the 3D printer affects dimensional accuracy and by matching the tolerances to the type of fit you need - sliding, interference or press fit - you increase the chances of your parts working together smoothly. For even more information on tolerances and mechanical fits, please see Wikipedia article on measurement tolerances.
With these guidelines in mind, you can order 3D prints that fit perfectly into your mechanical contexts - without unnecessary surprises in the form of too tight or too loose parts. Good luck to you!