Dimensional Accuracy
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Ensuring dimensional accuracy in your 3D prints is crucial, especially when creating large assemblies or parts that must fit together precisely. Several factors can impact this accuracy, including under-extrusion, over-extrusion, thermal contraction, filament quality, and even first-layer nozzle alignment.
First Layer Impact
The settings for your first layer can significantly influence the dimensional accuracy of your print. If the nozzle is positioned too high or too low, it can affect the next several layers. For instance, if you’re printing a 0.2mm thick layer but the nozzle is set 0.1mm away from the bed, the extra plastic may cause the first layer to be oversized. This oversize can impact subsequent layers, resulting in inaccuracies. To ensure your measurements aren’t affected by the first layer, consider printing a model with 50 -100 layers and measure only the top 20 layers. This minimises the influence of the first layer’s position. Verify that your measurements adhere to these guidelines before proceeding further.
Under or Over-Extrusion
Check your extrusion multiplier once you’ve confirmed that the first layer isn’t skewing your measurements. This setting controls the flow rate for the entire print. If the multiplier is too low, you might see gaps between perimeters, holes in the top surfaces, and undersized parts. Conversely, a too-high multiplier can cause bulging on top layers and oversized parts. Ensure that your extrusion multiplier is well-calibrated before moving on. For more advice on this topic, consult the articles on ‘Under-Extrusion’ and ‘Over-Extrusion’.
If the dimensional error increases with larger prints, you may be dealing with thermal contraction. This is common with high-temperature materials like ABS, which shrink as they cool. To address this, first calculate the shrinkage percentage. For example, if a 20mm wide part shrinks by 0.1mm, the shrinkage percentage is 0.1 / 20 = 0.5%. You can correct this by scaling up your model by 100.5%.