PrusaSlicer 2.9.4: Junction Deviation for Marlin and more accurate print time estimates

Prusa has released the final version of PrusaSlicer 2.9.4. The update focuses primarily on supporting “Junction Deviation” for Marlin 2 firmware and brings improvements to print time calculation. For users of FDM printers with Marlin, this version primarily represents a fine-tuning of motion planning.

Junction Deviation does not simply replace Marlin’s classic jerk model, but offers a different way of controlling speed changes at edges. Instead of just limiting abrupt direction changes, the algorithm takes into account how much the path actually curves. This is intended to enable fast movements at corners without visibly increasing vibrations or ghosting.

The new parameter “machine_max_junction_deviation” can be found in the printer settings under “Machine Limits.” As soon as a value greater than zero is entered there, PrusaSlicer automatically writes the appropriate M205-J command into the G-code. If the value is set to 0, the previous jerk model remains active and Junction Deviation does not take effect. For the CORE One L, Junction Deviation is already active in the profiles by default, with other printer models to follow gradually.

At the same time, Prusa has adjusted the internal time estimation and the G-code viewer. Both components now simulate the behavior of Junction Deviation. This gives users more realistic speed curves and significantly more accurate print time estimates, especially for models with many short segments or sharp direction changes. This makes it easier to plan longer print jobs and utilize machine parks.

In addition to the new motion functions, PrusaSlicer 2.9.4 also fixes a bug in the Arachne extrusion module. Simplification of closed paths sometimes generated extremely short G-code segments, which could cause visible artifacts on curved surfaces. The correction is based on a fix from OrcaSlicer and is based on analyses by the community around @sethml and @Noisyfox.

The update is rounded off by updated translations, including German, French, Spanish, and Japanese. For many users, 2.9.4 is likely to be less of a major version jump and more of a targeted functionality and stability update—especially for Marlin-based printers with a focus on precise motion control.