Ember has an impressive ability to structure material with far more precision than many other 3D printers. Depending on the resin used, it can print layers between 10 and 100 microns thick with XY resolution of 50 microns. While low layer heights are often useful for printing certain structures, in everyday use, I like printing at higher layer heights for the following reasons:
- It's much faster than lower layer heights
- There are fewer exposures and statistically, less chance of an exposure-related print failure
- Fewer exposures also means less wear on the PDMS window, likely increasing its service life
- The human eye cannot reliably distinguish 10um from 25um from 50um layer heights
To demonstrate the relationships between layer height, print time, and print quality, I chose two very different geometries: a lattice of my own design and a scapula from Thingiverse (both attached). The lattice is composed of delicate 500um struts while the scapula is a complex organic shape. I scaled both to a height of 42.54mm (40mm + 2.54mm of supports for the scapula) and then printed each files at 25um, 50um, and 100um layer heights in Autodesk's standard clear prototyping resin.
As can be seen in the photos, both geometries printed at all three layer heights and for many applications, higher layer heights don't diminish print quality.
Step 1: Layer Height and Print Time
Because increasing layer height increases the amount of resin that must be cured with each exposure, the exposure time must be increased as well. A further complication is that different features often require different exposure settings. Fine "positive" features, such as the lattice struts, require a slightly longer exposure time than geometries with higher cross sectional areas, like the scapula. Additionally, I turned off "variable exposure" for the lattice to ensure full curing of the small struts. A can be seen in the graph, it was nearly 200% faster to print at 100um layers than 25um layers.
Scapula print times and exposure settings:
- 25um: 2:34 min, 2.5 second exposures
- 50um: 1:23 min, 3.5 second exposures
- 100um: 0:46 min, 4 second exposures
Lattice print times and exposure settings:
- 25um: 3:01 min, 3.5 second exposures
- 50um: 1:45 min, 4.5 second exposures
- 100um: 1:03 min, 6 second exposures
Step 2: Under the Microscope
When viewed with the naked eye, there are subtle differences between objects printed at different layer heights. These differences become clear under 200x magnification.
Viewing the scapula along the print axis (Z-axis), the different layer heights are visible as steps of different sizes along the curves of the model. When viewed transverse to the print axis, the layers and their edges can be clearly seen. The difference between 25um and 50um is still not very pronounced, but the 100um layers create small overhangs due to the diminishing light intensity as light penetrates into the resin. This micro-scale feature manifests largely as a "frosted" surface to the naked eye.