Do you mould fast but surfaces show waves and artefacts? Are corners rounded or with excess material? Input Shaper and Pressure Advance are the two firmware features that transform high-speed print quality. Available on Klipper and RepRapFirmware (with slightly different names), they are what separates a mediocre 200 mm/s print from a perfect print.
Input Shaper: eliminating ghosting
Ghosting (or ringing) is the wave-like artefact that appears on surfaces after abrupt changes of direction, typically visible as 'echoes' of edges and letters. The cause is the mechanical resonance of the printer: when the head changes direction rapidly, the structure vibrates at its natural frequency and these vibrations imprint themselves on the print.
The Input Shaper measures these resonance frequencies with an accelerometer (ADXL345) mounted on the printhead, then applies a software filter that compensates for the vibrations by changing the acceleration profile. The result: smooth surfaces even at high speeds.
How to calibrate the Input Shaper
Mount the ADXL345 accelerometer on the printhead (on Klipper via SPI, on RepRapFirmware supported natively on Duet3D boards with built-in accelerometer). Run the resonance test from the firmware (SHAPER_CALIBRATE on Klipper, M593 on RRF). The firmware analyses the measured frequencies and suggests the optimal shaper type (MZV, EI, ZV) and cutoff frequency. Apply the suggested values in the configuration. Print out a test cube to verify the disappearance of ghosting.
Pressure Advance: perfect angles
Pressure Advance (PA) compensates for the delay between the extrusion command and the actual output of material from the nozzle. When the head accelerates, PA increases the pressure in advance; when it decelerates, it reduces it in advance. Without PA, the angles show excess material (blobs) at deceleration points and lack of material at acceleration points.
How to calibrate Pressure Advance
On the Klipper: print out the PA calibration template (tower with PA value increasing from bottom to top). Observe at which height the corners are sharper and the extrusion width more constant. That PA value is the optimal one. Typical values: 0.03-0.08 for Direct Drive, 0.3-0.9 for Bowden. On RepRapFirmware, the equivalent parameter can be configured with M572.
The Order Matters
Always calibrate the Input Shaper first and then the Pressure Advance. The Input Shaper changes the acceleration profile, which influences the pressure behaviour in the extruder. If you calibrate the PA before the Input Shaper, you will have to recalibrate it afterwards.
What you need
For the Input Shaper: an ADXL345 accelerometer (available at DHM-online), temporary mounting on the printhead, and a compatible firmware (Klipper or RepRapFirmware on Duet3D boards). For the Pressure Advance: only the compatible firmware and a calibration template (free download).
Accelerometers and boards at DHM-online
At DHM-online you will find ADXL345 accelerometers, Duet3D boards with integrated accelerometer, Raspberry Pi for Klipper and all accessories for a complete setup. See also our guide to Raspberry Pi 5 for Klipper on the blog.
Input Shaper and Pressure Advance: Optimising for High Speed
1. What is ghosting and how does Input Shaper solve it?
Ghosting (or ringing) manifests as a series of waves or echoes on the surface of the part, caused by the mechanical vibrations of the printer during sudden changes in direction. The Input Shaper is an algorithm that 'predicts' these vibrations and cancels them out by modulating motor accelerations. Using an ADXL345 accelerometer, the firmware identifies the machine's natural resonance frequency and applies a software filter that allows printing at high speeds without compromising surface aesthetics.
2. Why is Pressure Advance critical for print angles?
Pressure Advance (or Pressure Control) compensates for the inertia of the melted filament inside the extruder. Without this function, residual pressure in the nozzle would cause an excess of material (blob) in the corners, where the head slows down, and a lack of material on restart. Correctly calibrating the PA value results in sharp corners, uniform walls and perfect closure of the upper layer, eliminating unsightly "scars" on direction changes.
3. What is the difference in calibration between Direct Drive and Bowden systems?
The length of the filament path drastically influences the Pressure Advance values. In Direct Drive systems, where the extruder is above the nozzle, the values are very low (typically between 0.02 and 0.08) because the response is almost immediate. In systems Bowden, due to the compression of the filament in the long PTFE tube, the required values are much higher (0.3 to 0.9). Precise calibration is essential to avoid under-extrusion or excessive stringing.
4. How is the ADXL345 accelerometer used with Klipper?
The accelerometer is temporarily mounted on the printhead (and sometimes on the platter for "bed slinger" printers) and connected to the SPI pins of a Raspberry Pi or dedicated board. Using the SHAPER_CALIBRATE command, the firmware moves the axes at different frequencies, measuring the mechanical response. Once the resonance graphs are obtained, Klipper automatically suggests parameters (such as MZV or EI) to be entered in the printer.cfg file to stabilise the machine.
5. Why is the calibration order important for final quality?
It is essential to always calibrate the Input Shaper first and then the Pressure Advance. Because the Input Shaper alters the way the printer handles acceleration and speed, it also alters the pressure dynamics inside the nozzle. Performing the calibrations in the correct order ensures that the Pressure Advance value is calibrated to the actual movement behaviour of the optimised machine. At DHM-online you will find all the necessary hardware components, from accelerometers to boards Duet3D, to turn your printer into a high-speed machine.
