Calibrating a 3D printer: flow, pressure advance and input shaping

Highlighted terms are explained briefly when you hover over or tap them.

A good standard profile gets you a long way. But if corners bulge, top surfaces have grooves or walls are not quite closed, the cause is often values that do not quite suit the material or the printer. A few calibrations let you get these values under control. The order matters, because the settings build on each other.

The order

The OrcaSlicer documentation recommends this sequence:

In older guides, flow often comes before pressure advance. The two influence each other a little. If you notice after the flow calibration that the corners are no longer right, simply do pressure advance again.

Temperature, volumetric flow, pressure advance, flow and retraction depend on the filament and are saved in the filament profile. Input shaping depends only on the mechanics and applies to all materials.

1. Temperature

With a temperature tower you print several sections at different temperatures and compare surface, bridges and strings. How this works and which ranges are usual for which material is covered in Setting the print temperature.

2. Maximum volumetric flow

This test shows at what amount per second the hotend can no longer keep up. By default OrcaSlicer starts at 5 mm³/s and increases to 20 mm³/s in steps of 0.5. You measure the height at which the surface gets worse, and calculate:

Volumetric flow = start value + (measured height in mm × step size)

Example: defects from 19 mm height give 5 + 19 × 0.5 = 14.5 mm³/s. From this you subtract 10 to 20 % as a reserve. Why this value is so important is explained in Print speed.

3. Pressure advance

Filament is slightly compressed in the extruder. When the print head accelerates, the material arrives late, and when it brakes, the material keeps pushing. The result: corners bulge, line starts are thin, the seam is untidy. Pressure advance (called “Linear Advance” in Marlin and “Flow Dynamics” at Bambu Lab, the value is often called K) compensates for this by having the extruder push forward slightly when accelerating and pull back slightly when braking.

OrcaSlicer offers three tests:

• Lines: fastest, but strongly dependent on a good first layer.
• Pattern: angles made of several lines, easy to assess, several tests possible on one plate.
• Tower: independent of the first layer. You look for the height with the cleanest corners and calculate start value + step size × height.

On Marlin printers, Linear Advance has to be enabled in the firmware. That is not the case with every model.

4. Flow

The flow (also flow ratio or extrusion multiplier) scales the total amount fed. Too low leads to gaps and weak parts, see Under-extrusion. Too high leads to bulges and oversized dimensions.

With the test in the slicer

OrcaSlicer prints several small blocks with different flow values. You look for the block with the smoothest top surface without gaps. With the recommended “YOLO” test the calculation is simple: new flow = old flow + value of the best block. 0.98 and +0.01 becomes 0.99.

The classic way with calipers

Without a built-in test it works like this: print a cube with only one wall and no top. Measure the wall thickness in several places and take the average. Then:

new flow = old flow × target wall thickness ÷ measured wall thickness

Example: 1.00 is set and a line width of 0.45 mm. You measure 0.48 mm. New flow: 1.00 × 0.45 ÷ 0.48 ≈ 0.94. This method is less accurate, because even small measuring errors make a big difference.

5. Retraction

Retraction prevents strings during travel moves. The test prints several towers with increasing retraction length, and you choose the value from which no more strings appear. Direct drive extruders usually need significantly less retraction than Bowden systems. More in Stringing.

6. Input shaping

Every printer vibrates at certain frequencies. During fast changes of direction this produces waves on the surface, so-called ghosting. Input shaping controls the motors so that these vibrations cancel each other out.

OrcaSlicer offers a frequency test and a damping test for this for Klipper, Marlin and RepRapFirmware. You print a tower at very high acceleration, look for the height with the smallest waves and read the frequency from it. The OrcaSlicer guide recommends repeating this about once a year or after mechanical changes, for example after new belts or moving the printer.

What modern printers do themselves

Many current printers take part of this off your hands:

• Input shaping: printers with a built-in accelerometer measure the resonances themselves, often at first start-up or via a menu item.
• Pressure advance: some machines calibrate the value automatically before printing, for example with a sensor on the print head or on the bed. Bambu Lab calls this Flow Dynamics Calibration.
• Bed mapping and Z offset: almost all new printers measure these themselves.

What usually remains: temperature, flow and retraction for new filaments. With manufacturer filaments that have a ready-made profile, you can often skip them entirely.

Tips

• Only ever change one thing at a time.
• Save the results in the filament profile, ideally with the manufacturer and colour in the name.
• Damp filament falsifies all tests, so dry it beforehand.

Next: OrcaSlicer, where you will find all the tests in the “Calibration” menu.