Layer height, Layer Height, all I see is Layer Height
When choosing the next 3D printer and poring through the 3D printer specification, one of the metrics is usually more prominent than the others: the Z resolution aka the 3D print layer height.
Additive Manufacture (AM) has been around since 1981, with Chuck Hull of 3D Systems filing his patent in 1984. In 2009 FDM (Fused Deposition Modelling) printing process patents expired, and there was an explosion in new manufacturers (and technologies) hitting the market.
Desktop 3D Printing in FDM technology became available more widely since this time. The Holy Grail in 3D printing for some manufacturers was affordability; for others usability; and for some, sadly the sacrifice of precision for price was too tempting.
This Z resolution became the first major numerical differentiation between these early desktop 3D Printers in the late noughties. Early machines struggled to break the 1 mm barrier, but now layer heights on FDM printers can be sub-0.1 mm thin, while the older SLA (Stereo Lithography Apparatus) machines are even more precise.
The MakerBot range of machines have an advertised minimum layer height of 100 microns, whilst settings allow you to print up to 300 microns (and beyond) This selection of layer heights gives the ideal balance of speed and resolution.
The question morphs from:
What layer height can the 3D printer achieve?
What is the best layer height for the 3D print?
Are Lower Layer Heights Better?
High resolution has a trade-off. Thinner layers mean more repetitions, more passes by the extruder. This in turn means longer 3d print times: 3d printing at 25 microns vs. 100 usually means and increase in the print time four-fold. More repetitions also mean more opportunities for something to go wrong. There is NOTHING more soul destroying than leaving a 12 hour print to return to failure.
To put this into context, even at a 99.99% success rate per layer, quadrupling the resolution as above from 100 microns to 25 microns lowers the chance of print success from 90% to 67% if the assumption is that a failed layer causes total print failure.
Examining the 3D Prints in the image it is fun to try to guess which model was made at 50 microns, which at 100 microns and which at 150 microns (µ)
It might be a surprise to learn that the print on the left is 50 µ , middle is 100 µ, right is 150 µ.
The stringing and blobbing in the 50µ model is due to several factors:
The Z Axis Offset, Extrusion Rates and Retraction settings
If the hot end is lower in the Z axis than it should be, pressure will build up in the hot end that will need to find a release in any way possible regardless of retraction settings. This ooze will occur from the side of the nozzle. Stringing will occur as this filament is pulled out having adhered to the model when the hot end moves on. The effect can also cause filament jams.
If the hot end is higher (too far away from the model in the Z axis), the extruded filament will not properly bond to the previous layer and it will be stretched out when the hot end moves.
The same issue applies with extrusion factors and settings (speeds). Extruding too much for very low layer heights will cause excess filament blobbing where it's not desired. This adheres to the nozzle. It is then dragged out of the nozzle and is mistaken for oozing. Too little extrusion and the layer being extruded will not bond to the previous layer and stringing occurs again.
Retraction settings are to stop oozing (filament drip) from the hot end during non-extrusion movements. Although retraction settings do not help with filament that is already improperly extruded.
Therefore lowering the layer height requires some other fine tuning of print settings in order to make successful models, but also is only appropriate for some models.
Lower layer thickness equates to more time, and more errors.
Do thinner layers yeild better prints?
This Depends: it depends on the 3D model to be printed and also the XY resolution the 3D printer is capable of. In general, thinner layers equals more time, and the possibility of more errors. Therefore, it is true that in some cases, printing models at lower resolutions (i.e. thicker layer heights) can actually result in higher-quality prints.
When Lower Layer Heights are NOT Helpful
Lower layer heights are typically associated with smoother transitions on diagonals, which leads to generalisation and a push of Z resolution to the limits.
However, if the model consists mostly of vertical and horizontal edges, with 90-degree angles and few diagonals additional layers will NOT improve the quality of the model. (see illustration)
Layer Height Improvement
The issue is compounded if the XY resolution of the printer is not perfect.
If the printer does not have good X-Y resolution then more layers means more mismatched ridges on the surface. While the Z resolution is higher, the model will look like it is significantly lower quality in this case.
When to Choose Higher Z Resolution
There are times when higher resolution is desirable.
Given a printer with good XY resolution and a model with intricate features and many diagonal edges, lowering the height of the layers will yield a much better model. In addition, if that model is not tall in the Z axis (200 or fewer layers) then increasing the Z-axis resolution can really improve the quality.
In a nutshell, 3D printing smaller objects will benefit from lower layer heights.
Certain designs benefit from a higher Z resolution: organic forms, rounded arches, small embossing, and intricate engravings.
If the desire is to print small objects, then FDM 3D printing might not be the solution, and perhaps SLP (Selective Light Processing) or DLP (Digital Light Processing) 3D printing may be the better solution.
These technologies require more post-processing including curing the model in UV light to harden it post 3D print.