Introduction
Due to workload, life and other things, my printer had been sitting idle for a few days. Patiently… Quietly…
The kind of quite that speaks volumes. Enceclopedias in fact!
About love and loss and hurt …
Once it got over the initial sulking phase, it decided to fight! Quietly muttering some comments straight into my little brain.
“Is that dust on my rods?”
“I am feeling creaky. Where was that lube again?”
“Do my belts feel loose to you?”
When it arrived at “Remember the last time you made me rock the bed?” I knew I needed to shut it up…
Why?
As a hobbyist, “Because!” is enough of an answer for me 
.
But there is indeed a bit more to it.
Having been torn between an X1 and a resin printer back 2023, I was always wondering how fine a surface we could get out of FDM. This stems from an experience with a scale model I had ordered printed for an R&T project we were working on at the time. Printed with a 0.2mm layer height, I knew I had to do some serious post processing to make it truly unique. Of the roughly 160h I spent on sanding, painting, decal creation/printing/application and subsequent sealing with two coats of clearcoat, around 3/4 of that time was spent on working my way through the sanding grits.
120h can “buy” a lot of extra print time. Especially, if I am free to do other stuff while the printer is laboring away. So if the layers can get so fine that post-processing is no longer neccessary, it is an instant win. In particular if it can generate smooth surfaces which I would have no chance whatsoever of sanding with my available equipment.
As such, I expect that the question of truly minimal layer heights can be of interest not just to me, but also to others. In particular those doing miniatures or aerodynamic RC prints or anyone “loving” post-processing as much as I do.
A benchy to warm up
So with the exercise initially being triggered by a need to give the printer something to chew on, I just followed some older threads advise.
Set minimum and maximums for variable layer height? - Bambu Lab Software / Bambu Studio - Bambu Lab Community Forum
Lowest possible layer height? - Bambu Lab P1 Series - Bambu Lab Community Forum
I changed the lowest possible layer height to 0.008mm, used the adaptive infill to get everything to its minimum, enabled “Infill combination” and sent it to the printer which was sporting the .4 hardened nozzle and used my Bambu PLA Basic white throughout.
Well. Nothing to write home about. Except…
- I originally wanted to learn not only how low we can actually go, but also how the prints would fail. The artifacts however, were (at first) a bit difficult to interpretate.
- THAT ROOF TOP SURFACE WAS AMAZING!!! An ironed feel on a shallow angled surface!!!
As with all good “simple” questions, the original question did not lead me to an answer but to further questions:
- Was that a fluke? How good is a benchy for the minimum layer height question anyway?
- Did those flow issues come from the nominal layer height? Or was the infill combination to blame? Note: It defaults to a massive 100% nozzle diameter height with adaptive layer height enabled in Bambu Studio.
So I needed a few simple trials to more efficiently separate and address these questions
First, I narrowed down the interesting geometries. With high overhangs, as I use them, their quality is mainly dependant on the support interface, so not really the first question to be addressed.
But shallow dome like structures would serve well as simple, quick test pieces.
Changing a few settings…
This came out of the printer.
Although some flow issues are apparent on the pic’s already at 0.025mm nominal layer height, I took the pic in particular to highlight defects. It is actually a pretty well feeling print but layer lines are still audible when running a fingernail across its surface.
This trial run also enabled me to determine that the initial flow issues were not from the “Combine infill” function. Although most older posts on minimum layer lines go on about microstep of the z-motors, they actually have nothing to do with failure modes at true minimal layer heights. Failures appear to be driven by the fine control capabilities of the extruder:
This is where I got truly curious and finally gave in to my printer to do some much needed cleaning, tensioning and lubing.
Some software stuff
I was also certain, that with Studio’s handling of combined infill, I needed something different. Of course, that was when my SD card played up, Studio was acting a bit strangely and the firmware complaint from lack of updates…
I was finally forced to upgrade the firmware, install the latest versions of Studio and Orca, and, the key item in all of this, enter Developer mode to tick the box to accept that I knew that all mistakes while in developer mode are my own with no liabilty claimable from Bambu. That probably could have been simpler.
I felt it neccessary to go through that though as Orca handles “Combined Infill” very differently from Studio. In particular, it does allow the setting of a maximum combined layer height. That is also important for pretty much all “Adaptive Layer Heigth”, “Combined Infill” prints as Studios default of 100% nozzle diameter leads to rather messy infills which can translate to the top layer. In fact, setting a non-user controllable default higher than the allowable maximum layer height of 75% nozzle diameter may merit a bug-report for Bambu Studio .
A smaller nozzle allows a lower layer height. Right?
Finally being able to progress, I installed the 0.2mm nozzle. After all, the minimum layer is stated as being dependant on nozzle size throughout the net. Surely, if it is written all over the net, it’s got to be right? Right? Especially when the major slicer all use nozzle size as a prime determinant of the minimum layer height?
Let’s get back to that particular question in a little while. First, let’s take a look at some quarter lenses printed with a 0.2mm nozzle at different layer heights:
So what are we actually seeing?
The lowest row is, from left to right, printed with nominal layer heights of 0.1, 0.05 ,0.025, 0.0125 and 0.006mm. I aborted at 0.006 as it was obvious that this was not going to end well. I realised that there was an unfortunate misconception in the GUI-user interaction during this test series and could not be certain that results were valid (*). So I repeated the most interesting data points, the 0.0125 and, accidentally, the 0.003mm.
==> Turned out the first row was valid. 0.025mm worked well, 0.0125mm was a close but nevertheless clear failure.
(*) OK, I screwed up in having overlooked that Orca defaults to a Cool textured plate… which I don’t even own… amazed it still worked…
Having already determined that flow control is the key parameter for failure at extremely layer heights, two obvious parameters came to mind when trying to avoid messing with the full object flow ration:
- Increase the speed
- Increase the wall width
That is the middle specimen. It is always a bad idea to change two parameters at the same time…
The second row from the top shows the same as the ones below, only that this time, only speed and accelerations were increased by a factor of 2. With flow issues being audible early on, I chickened out again.
The top row shows 0.0125mm and 0.006mm layer heights with a wall thickness increase by 50% to 0.33mm.
What can we take away from this?
- Halving the nozzle diameter does not actually do anything to improve the achievable z-resolution. In fact, with the reduced flow through a smaller nozzle, flow control can only be expected to be more difficult with a smaller nozzle than with a larger nozzle.
- Increasing flow is key to achieve extremely fine layer heights.
- With the failure mode drastically changing from the ribble effect associated with minimum flow to a very different edge exfoliation type attributable to local overextrusion at shallow outer edges, there’s either a tipping point or optimum value in between 100 and 150% wall thickness. If such a processing window is actually wide enough to be useful is not currently clear.
How about achieving a better z-resolution by simply increasing flow through the use of larger nozzles?
Going back to the 0.4mm nozzle, the lowest row shows the 0.0125 and 0.006mm layer height prints with the basic settings for comparison.
The upper row shows the same prints but with a wall thickness increased to 150% or 0.66mm.
So we can confirm that the 0.2mm nozzle findings apply here as well although performance appears slightly better due to the higher default flow.
Maybe we should look at the 0.8mm nozzle to increase flow? A higher flow should be more controllable. And print times would go down again 
.
Sadly however, this was a desired result that eluded me. With the larger nozzles having disappointed many due to the overal extruder-hot end-nozzle system being truly optimized for the 0.4, they only really shine in specific use cases such as transparent material printing.
Of course, this was only a short test series thought and carried out between coffee breaks while answering mail #32 of the day and slide #138 preparation while the kids were chasing the dog around the house (or vice versa, can’t remember), but I needed to write this down now to get my head clear for next weeks madness.
In particular, since I am still angry about the articles and posts claiming to know that my minimum layer height should be purely on the baseless claim to know what print times all possible use cases can accept. My use case, my trade!
Key takeaways:
- Nozzle size has little to do with achievable minimum layer height. It affects achievable XY-resolution, but has no direct effect on Z-resolution in a stiff printer.
- Nozzle size affects the primary failure mode when printing extremely thin layers. As such, a smaller nozzle will lead to reduced flow, meeting the failure flow earlier than a larger nozzle.
- Minimum layer heights of 0.03mm appear to be low-hanging fruits for the X/P-series. By lowering the limits below the defaults, the user can freely use adaptive layer height to trade increased print times for reduced post-processing time.
- Combined Infill is not handled well in combination with adaptive layer height in the current (23 March 2025) version of Bambu Studio due to it defaulting to an overly large layer height. This is implemented much better in Orca. Hopefully, we will see this in Studio soon, too.
- Increasing the wall thickness can likely help to find a processing window for extremely fine layer heights of 0.0125mm or even 0.006mm. The data points of 100% and 150% default wall thickness used here mark the extent of the range yet to be investigated.
As mentioned, I needed to get this out of my system before embarking on the next demanding week. I may or may not return to the topic but either way, I do hope that this will be useful, or at least interesting, to others.
Next?
If I do return to the topic, there are a couple of things that come to my mind:
- Further investigate the wall thickness increase as a means to achieve a really good surface for a 0.0125 or even 0.006mm layer height by attempting to narrow down likely processing windows.
- Alternatively, directly alter the flow ratio (although I expect that this will not end well and is certainly not usable with adaptive layer height).
- Run a few trials with the 0.6mm nozzle.
- See if the narrower heat chamber of the Plus 4 leads to a better (or worse) flow control at extremely fine layer heights.
- Look at PETG.
- Identify the principal minimum layer height failure mode for wood PLA and carbon filled material (PETG, PC, PPS on the Plus 4).