[JMay]

For 3d printing one of the key abilities of any printer FDM or resin to produce good prints is the minimum layer thickness it can print.

To explain, below is a ball or sphere 50mm diameter drawn on CAD.

   

Take the CAD file to the printer ‘slicer’ software and it turns the sphere in to a collection of plates each plate is the layer thickness set.

   

This is at 0.5mm layer to show the concept of the overlapping plates forming the sphere and the steps are quite apparent. In practice this would require aggressive post print sanding to smooth out these steps.

Same file now at 0.1mm layer (usually the best most FDM printers can achieve and the steps are much finer but still there so will still need some sanding.)

   

Resin printers can offer much finer resolution i.e. 0.02mm and the steps at this setting are now indistinct in the overall curve. 

The above is an introduction to the importance of the layer thickness if you wish to print body shells that don’t look like Lego plates stacked up.

Now for some real world testing on a FDM printer (Creality CR Mini). Taking the rear quarter of the Aston DBR1 that I sectioned for vertical printing, this part has curves in 3 planes so an ideal real world test piece as only 14 minutes to print at 0.24mm layer.

   

1st up 0.24mm layer

   

Steps clearly visible

0.12mm layer

   

0.12mm is a common setting for fine printing.

0.1mm layer

   

0.1mm is the stated limit of many FDM printers including the CR 10 Mini.

0.08mm layer

   

Most printers can go to 0.08mm which gives a good result, some can go down to a stated 0.05mm.

0.04mm layer

   

0.08 & 0.04mm, side by side

This shows the printer did achieve a better resolution than 0.08mm (and better than the stated minimum of 0.1mm) by how much I can’t measure but overall it does look better than 0.08mm layer height.

The 0.04mm setting was achieved using the standard 1.8 degree stepper motors that came with the CR10 Mini. I dialled this setting into Cura crossed fingers and watched as it printed. Why try down to 0.04mm?, this came from a comment attached to a recent printer review where the new printer has 0.9 degree stepper motors on all 3 axis including Z or layer control. In theory these stepper motors should be capable of finer and more consistent resolution than the 1.8 motors. In the comments below the review, one of the comments stated that 0.04mm can be achieved using the 1.8 degree stepper motors in older printers.

As stated all printed on a Creality CR10 Mini converted to direct metal filament drive, some frame stiffening but otherwise as it came from Creality.

Settings

Material PLA (Esun ePLA-ST)
Nozzle 200C
Bed 60C
Outer wall speed 40mm/s
Overall speed 80mm/s
100% infill.

The 0.04mm setting is interesting but the flip side is a 24 hour print time instead of 10 hours to do the Aston DBR1 complete, so for myself more practical for printing smaller objects i.e. drivers or engine detail.


Cheers 
            John

[Kevan]

That's a really good post for those wanting to understand what a 3D printer does. 

I always work in increments of 0.04mm which is commonly called a 'magic number' by 3D makers, although not a specific stop point is a half-way between two 'steps' a stepper motor is capable of.

[MrFlippant]

One of the features I really like in the various branches of Slic3r (PrusaSlicer, SuperSlicer, Bambu, etc.) is the "Variable Layer Height" option. You can let it automatically figure the best layer heights for the entire model, or manually configure them. With this feature, you can use thicker layers in the more vertical surfaces for faster printing time, while having the thinner layers at the tops of curved surfaces or near-horizonatal surfaces. You often get a significan't savings in print time as compared to printing the entire model at the very fine layer heights, but still get the benefits of the reduced stair step effect.

[Kevan]

I've never tried that feature, not sure I can trust it 100% to decide where the thick layers need to be 

[Savage GT]

Nice informative post, thanks John 
I didn't realise I could go below 0.1mm layer height, but like you say a big increase in times.
Kevan, I use the slicer from Creality, which is pretty much rebadged Cura software. You can preview the print to see where it is doing the finer layers on the variable layer height, I should imagine so do most others.

[Kevan]

I use Prusa slicer, it does the same

[Kevan]

layer height also has a bearing on print strength, a great video here ->

[chappyman66]

The OP is another good illustration of FDM layer heights.

This is why I have always run bodies at 0.06 layer height (exactly half a step between).  The Ender3 is plenty capable of running at 0.04 but the already lengthy print time is extended another 50% so I don't do it.   I don't sand for hours, it isn't required at those layer heights.

Note that the resolution / quality of the file makes a significant difference in finished body quality as well.  A low-poly body will still look blocky even printed in resin.

   

[MrFlippant]

I've never tried that feature, not sure I can trust it 100% to decide where the thick layers need to be 

I'd say I'm about 50/50 with respect to how many prints I use the automatic versus how many I either set manually or adjust after automatic. The tools to manually set, or adjust, are quite robust. In some rare cases, I'll use the Height Range Modifier option to set a layer height right up to a specific layer, and then a new layer height from there.

The tools really are quite powerful if you spend some time to play with them, beyond just setting a specific layer height for the entire print.

That said, some prints need a fine layer height from start to finish, so setting variable height saves nothing. The example in the OP is probably one of them.