One of which I was well aware of, but to which I haven't been paying enough attention.
I came to the end of a reel of FDM filament, and started a new one. Same make and type of polymer, same colour. Just from a later batch: eSun PLA+ brown.
I printed the exact same file on the Neptune2S and was a bit surprised that from the old reel the chair sockets had been a fraction loose, but from the new reel they were far too tight.
The problem wasn't difficult to find:
old reel filament diameter: 1.72mm
new reel filament diameter: 1.78mm
That's not much difference (2 thou), and within eSun's claimed spec: 1.75mm +/- 0.05mm.
But it's enough to make a significant difference to plug track. The filament diameter is a critical dimension because it gets squared in the calculations of polymer flow, so small changes make a big difference:
1.72 / 1.78 = 0.9663
0.9663 x 0.9663 = 0.934 = 93.4%
That means that to correct for the change of filament it is necessary to change the Flow setting in the slicer to 93.4% of what it had been for the previous reel. i.e assuming 100% previously:
View attachment 6770
It is particularly critical to get the flow right for plug track, because I also use this setting in Cura:
View attachment 6769
which is showing in yellow because that is way above the expected range up to 100% max.
What that does is to allow the printer to print narrow walls accurately (such as the socket walls) which are significantly narrower than the nozzle diameter (0.4mm) by carefully reducing the flow rate along them.
What to do about all this? I can't imagine many users wanting to do filament volumetric calculations every time they change a reel, and make consequent changes in the slicer settings.
It will at least be necessary to measure the diameter when starting a new reel, and ideally before each fresh job. So a suitable caliper or micrometer will be a tool needed for FDM plug track. I imagine most users will already have one -- inexpensive digital calipers are often available from Lidl, etc.
The measured diameter could then be entered in Templot. Which could adjust the socket clearances to allow for the change in polymer flow. Leaving the slicer set on 100%. Then it's only necessary to re-export and slice the file if making multiple identical parts.
So that's yet another tickbox and a chunk of code for me to write.
Either way, it's unlikely to be a perfect correction. There will likely also be batch-to-batch changes in the polymer thermal and shrinkage characteristics. And a change in diameter may affect the speed at which it is fed through the extruder gears. And I haven't kept any records for the consistency of diameter throughout a reel. But it would probably go most of the way to correcting for the filament change and be a usable result. Only a full trial and error test will get a perfect result.
cheers,
Martin.