The current flow rate (extrusion multiplier) calibration in either Bambu Studio or Orca Slicer has two major pain points:

• It can be really hard to tell which surface is the smoothest by visual or tactile inspection especially on light colored filaments
• The choice for the smoothest surface can be subjective without an explicit criteria

Here I introduce a new method to decide the smoothest surface with an explicit and easy to follow criteria, hopefully this will help everyone's life easier trying to do the flow rate calibration for new filaments. To understand how this works and use this guide, you'll need the prerequisite knowledge on how flow rate calibration works, which can be found at: Ellis' Printing Guide.

Only works in Orca Slicer for now, but the flow rate value is a filament property that applies to both Bambu Studio and Orca Slicer

*Disclaimer: this is my weekend project, and I don't have the time to polish this process much. If you find this to not work as well in your case, I'd appreciate it if you could comment and even help improve by adding your remix. Thank you and happy holidays!

What's the new method?

After printing the flow rate calibration print, use marker or acrylic paint pen with a different color (black marker on white filament, or yellow on black filament) to paint the center of each print, then immediately use a paper towel to wipe the surface before the paint dries. The idea is that the marker adds contrast and depending on what's wiped off, it's very clear what the surface smoothness looks like. More details below, with black marker on white filament (Sunlu PLA plus white) as an example:

Steps:

1. Put the marker at the center of each block and immediately wipe the surface with paper towel before the paint dries, but don't wipe off everything. In the photo the flow rate range (top to bottom) is 1.04 → 1.02 → 1 → 0.98 → 0.96 → 0.94:
2. Look closely at the painted then wiped part. If the paint is only wiped off between the extrusion lines (two extrusion lines meets and over extrusion causes molten plastic to be squished up between the lines), that means there's an over-extrusion. If the paint is wiped off more or less evenly on the extrusion line and between the extrusion lines, that means the surface is smooth. If the pain is wiped on the extrusion lines but remains between the extrusion lines, that means there are gaps between the extrusion lines, so under extrusion. It's pretty clear if you look by eye, but I can't take good enough photos. So I used an electronic ear-pick with camera to take the photo which are attached below. High flow rates like 1.04 has wiped clean areas mostly only between extrusion lines indication over extrusion, and flow rates like 0.94 has paint left unwiped mostly between extrusion lines indication gaps and under extrusion. The best flow rate is 0.98, where areas on-extrusion-lines and between-extrusion-lines look roughly equally as clean (or dirty), so I pick this value.

Have I done any control experiment?

Yes, as you can see from the photos above, I tested this on Bambu basic PLA black with yellow paint, and got 0.98, which is the value Bambu gives for their filaments.

How to use the uploaded 3mf file here?

I've uploaded a 3mf model file with the following improvements compared to the baked in flow rate calibration model, only works in Orca Slicer:

1. all cards are grouped together into one piece, the built-in model has 10 pieces
2. added a two infill layer to separate the top test layer with the first layer, as suggested by Ellis' Printing Guide

To use them, follow these steps:

1. open the 3mf file in Bambu Studio or Orca Slicer
2. set your filament flow rate to be 1
3. Change the flow rate of each block to the values you want to test in the Objects independent setting in Orca Slicer:
4. print the file and find the smoothest surface based on the steps described above.