This Fix for Oozing Saves Time and Filament

A faster and more precise method is the Pattern method found in Ellis’ Print Tuning Guide. With this method, the user prints a series of thin right angles with a gradual user-defined range of K-values, along with other user-defined printing parameters. This allows for a direct, clear top-view comparison of various K-values, allowing for a more accurate value to be determined. Simply select the K-value that corresponds to the sharpest corner – that is, the corner with least corner gapping or bulging.

The Pattern method is faster and uses significantly less filament to print. This is especially helpful given the fact that users may have to do this tuning often; Pressure Advance / Linear Advance should be calibrated specific to the printer and spool of filament the user intends to print.

More information and the G-code generator can be found in the Pattern method section of Ellis’ Print Tuning Guide.

The first thing you should do before diving into any Pressure Advance / Linear Advance tuning is to confirm that your printer’s hot end can manage the volumetric flow rate necessary to achieve clear test results. As we mentioned above, underextrusion and oozing are most likely to appear at high speeds, so the tuning process often calls for a high print speed. This will, in turn, require a hot end and temperatures capable of melting the filament fast enough to extrude properly.

Let’s say you’re printing the tuning test with a 100 mm/s print speed, a 0.4-mm extrusion width (also called “Line Width” in some slicers) and a 0.3-mm layer height, the printer’s hot end must be able to handle a volumetric flow of 12 mm³/s – which is a stretch for some stock hot ends. If your hot end can’t handle this, you’re likely to see severe underextrusion, resulting in poor layer adhesion and gaps in the print. Users may mistake this as an excessively high PA value when in actuality, they’re outrunning their hot end’s melting capacity.

Therefore, check your hot end’s max flow rate to ensure you’ll get accurate tuning test results. Depending on what you find out, you may have to adjust the print speed of the tuning test to match your printer’s melting capacity.

Tuning Considerations

Based on our experience, we have some important things for you to keep in mind when tuning with the Pattern method:

• Klipper’s documentation gives 100 mm/s as an example print speed, and you’ll also see this as the default print speed in Ellis’ calibration tool. That being said, if you normally print at higher speeds, you should tune Pressure Advance / Linear Advance based on your typical speed settings. For the best dimensional accuracy and part strength, use your outer perimeter speed and acceleration settings.
• Generally, the higher your printing speeds (print speed, accelerations, and decelerations), the lower your K-value. This is because higher speeds mean there will be less time for the hot end to ooze; therefore, the extruder doesn’t have to compensate as much.
• While very high K-values may look great in prints, it also results in high corner gapping. This can lead to a loss of part strength. Based on the test print results, it’s recommended to choose the sharpest corner with little to no gapping.
• If you’re getting weird results, it might be due to an inappropriate smooth_time value. While the smooth_time is ideally 0, this is impossible because the extruder isn’t able to instantaneously accelerate and decelerate. A high smooth_time limits extruder acceleration to prevent extruder skipping, while a low smooth_time can result in more precise corners but will require higher extruder accelerations. You can change smooth_time as low as your extruder permits before it starts skipping, but for reliability’s sake, don’t keep it too low – results are often diminishing in this aspect. For most direct extruders, 40 ms is a good start.
• Make sure to print a series of thin test squares using your newly obtained K-value. There shouldn’t be significant corner bulging or gapping. The middle square in the image above is a great example.

Finally, please remember that there is no “perfect” K-value due to the nature of the FDM printing process itself. A tiny bit of corner bulging or gapping is unavoidable due to the printing speed differences between the internal and external perimeter. Rest assured that it won’t affect your part’s dimensional accuracy or strength.

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