Why it can be important to calibrate - or at least to check

[user_3026326371]

We all love the load, click, print approach but sometime that just isn’t enough.
Prints fail or come out with bad artefacts, overhang issues and what not.
Did you know that it all starts with a properly calibrated filament?

Take a look at those 4 patches.
What do YOU think is wrong?

The applied ‘fix’, from left to right was to INCREASE the flow ratio…

If you ever did a filament flow ratio calibration you will now say that those results are not possible, at least not in that order.
Thing is that I cheated a bit to highlight the problem of judging what is cause and what might be effect.
I cranked the k-factor why up before printing those patches.
Instead of around 0.02 to 0.2 - WHAM…

I did this only give a really bad example.
In reality a slightly off k-factor has as little impact as a slightly off flow ratio.
The devil however is in the detail - literally.
What you see in the pic can happen quite easy if you got really nice prints in 0.2mm layers and decide to ‘quickly’ print something in, let’s say, 0.08mm layers.
With every new layer the problems just seem to get worse…

So what came first here, the chicken or the egg?
Perhaps the rooster I would say…
But jokes aside, the triangle formed by extrusion temp, flow ratio and k-factor gets more vital the finer the layers get.
Why? Simply because the thinner we go the less filament is extruded and every bit off ideal can mean troubles.

How do these three related to layer heights?
Thinner layers usually not only translate to slower extrusion volumes per mm but also often to different extrusion temperatures.
Going fast at 0.2mm or above means the filament does not spend too much time in the melting chamber.
Very thin means it takes like forever to get a few cm of filament going through…
Means the filament might start to get cooked.
Makes sense then to consider checking if with a lower layer height and speed you get better results adjusting the nozzle temp down by a few degrees.
The flow ratio explains itself really.
The more you are off the ideal the more it will affect thin layers, especially their solid infill.
Makes sense to at least check of the flow ratio is still ok for those 0.08mm layers or if it requires some tuning before starting a major print.
The k-factor is something that seems totally under-rated…
Print the pattern, take a quick look and enter the number to the right…
The above pic shows nicely what WOULD happen if your k-factor is just good enough for most 0.2mm prints but way off for 0.08mm.
On the other extreme, going far to low on the k-factor not really much (initially) happens.
That’s because the k-factor sort of limits how much filament is extruder for corners, the ends of infill lines but also the bridging anchors.
Most importantly though it also affects our overhangs to some degree, especially those that are not just plain, straight and basic.

Nice but in what order should I calibrate and is the Bambu calibration good enough?
The temp should be checked first - you don’t want any stringing and you want good layer adhesion.
Leave the standard k-factor and do the flow ratio first as otherwise it messes up the results too much.
Last but not least the k-factor.
Special case: Vase mode, here you want to calibrate the flow ratio so the line width in your settings matches the measured print.
To avoid wasting lots of filament I usually print a small cube without sparse infill and top layers.
If the measured wall thickness is off the printed part I adjust accordingly.
E.g.: 3 wall loops, inner walls 0.45, other wall 0.42mm, makes 1.32mm all up.
With an assumed set flow ratio of 0.98 and a measured wall thickness of 1.26mm >
0.98 divided by the measured 1.26mm then multiplied by the expected 1.32mm gives us 1.027 for our new flow ratio.
Another print of the same cube should result in matching walls.
The fine tuning with some top infill checks until I got rid of these saw teeth while neither having gaps between the infill lines nor a build up - just a nice and smooth surface.

So before you keep messing with print setting to ‘get things right again’ check your calibration.
More often than not you can find it a bit off …

[user_1295698772]

Good write up, I don’t see the relationship between temp, flow rate, and pa talked about much. My standard practice is to set temps on the high side, for layer/bed adhesion, but drop them down if three’s stringing, do a flow rate calibration, then pa cal, as you’ve said. I occasionally go down the tuning rabbit hole and do a second set of calibrations if I’m looking for better precision on details. Tuning changes don’t happen in a vacuum, a change to one setting affects the others, which unfortunately could lead to an infinite tuning loop. Don’t go too far down the rabbit hole.

[user_3026326371]

You are right with the rabbit hole, especially when trying to calibrate for very fine layers and 0.2mm nozzles.
I just thought pointing out a few things might help people new to 3D printing to consider to at least check their calibrations or what the Bambu defaults provide when prints keep failing.

When I started 3mm filament and a bowden system was the only option.
With the filament being anywhere from about 2.85mm to being too thick to fit on a single roll calibration was basically optional.
A few years later 1.75mm became available and soon the new standard.
With it the option to have an extruder mounted right on the print head - massive contraptions…
Calibrating started to become more important.
But modern printers with all in one profiles ready to go IMHO created a mess for newbies.
Expecting the advertised results and seeing a ruined print is not a good thing.

A flow rate calibration ending in a value like 0.972748 is just overkill.
And a k-factor selection based on the default range to end with 0.02 or 0.015 is good enough for almost all prints.
But once corners, the start and end points of layer lines or the infill struggles using fine layers it can help to find a balance between overkill and standard

[user_1295698772]

I wasn’t disagreeing with you at all, just sharing my own work flow (which often includes going down that rabbit hole lol). And you are right about the higher values, if there’s not a zero after the decimal on pa and flow isn’t real close to 1 you probably need to change the temp to get them there. The main issue that gives me problems there is turning up the temps to try to get bed adhesion(I avoid using glue). thanks again for the great write up. As I said, I rarely see a discussion about the relationship between different settings, so I’m glad you shared it.