The size of each 3D printed part and feature is important to consider. For example, large objects may not fit in a particular 3D printer, small features might not print with a high-enough resolution, and tall thin features might not have enough cooling time between layers, resulting in messy plastic globs. All of these issues relate directly to object size.

Consider the build size of the 3D printer. The typical 3D printing bed size is around 175mm x 175mm x 175mm (or 7 in x7 in x 7in). They can range between 90mm (3.5in) to ~400mm (16 in) for desktop FDM printers, (and are much larger for things like house printers).

If printed features are too
large for the printing bed, you can:

  • Scale down an object to fit the build area (account for the changes in tolerance when scaling)
  • Slice the model into separate, printable pieces

If printed features are small: 

  • The smallest printable feature size is usually twice the thickness of the extruded thread of plastic, or two times the diameter of the nozzle (0.4mmx2=0.8mm).  

Tall and Thin Features:
Sometimes tall and thin features are printed too quickly, piling on the molten plastic faster than it can cool, which results in globs of plastic:

The three most effective ways to reduce failures when printing tall or thin features are to:

  1. Slow down the print speed, and if possible, set a time delay between layers in the slicer.  
  2. Design a second tower of equal height (or print/design two of the tall thin features) for the printer to navigate to before returning, allowing the layers on the tall feature to cool. 
  3. Upgrade the cooling shroud around the nozzle, to cool the plastic faster. You can 3D print an upgraded fan shroud (just make sure to use a higher-temperature plastic, like high temp PLA, ABS or PETG).

In summary: The size of certain features, as well as how tall or thin those features are can affect how well they print. Keep small features at least 2.5x the thickness of the nozzle (~1mm for 0.4mm nozzle), to retain quality. Tall and thin features require extra considerations to print properly.

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