Learn & Understand

Retraction Speed and Pressure Advance: What Volume Alone Misses

Retraction volume tells you how much plastic gets pulled back - it says nothing about how fast that pullback happens, which turns out to matter just as much for avoiding both stringing and grinding.

Speed Is the Other Half of the Retraction Equation

The same retraction volume executed slowly versus quickly produces different results. Too slow, and the plastic at the nozzle tip doesn't fully retreat before the travel move begins, leaving enough residual pressure to ooze - similar to the effect of too little retraction volume in the first place. Too fast, particularly on Bowden setups with a meaningful length of PTFE tube between the extruder motor and the hotend, and the sudden yank can cause the filament to elastically "twang" - stretching slightly like a rubber band and then snapping back - which can momentarily over-retract or introduce inconsistency shot to shot. Tuning retraction speed alongside distance/volume, rather than distance alone, is necessary to actually dial in clean retraction behavior.

Bowden vs. Direct Drive: Why the Same Setting Behaves Differently

This "twang" effect explains why Bowden setups generally need more careful retraction tuning than direct-drive extruders, not just larger raw retraction distances. In a direct-drive setup, the extruder gear sits right at the hotend with almost no flexible tube in between, so a retraction command translates almost immediately and predictably into the nozzle tip retreating. In a Bowden setup, that same command has to travel through however much PTFE tube separates the motor from the hotend, and the filament itself has some compressibility and elasticity across that length - meaning the *effective* retraction at the nozzle tip lags and can differ from the commanded distance in ways that are highly specific to that particular tube length and filament stiffness.

Pressure Advance / Linear Advance: Reducing the Need for Retraction in the First Place

Rather than only reacting to ooze after the fact with retraction, modern firmware features - called Linear Advance in Marlin and Pressure Advance in Klipper - proactively manage the pressure buildup inside the hotend's melt chamber during printing itself. As the print head accelerates into a fast segment, the firmware slightly increases extrusion ahead of time to compensate for the pressure that's about to build; as it decelerates, it backs off extrusion slightly early. This keeps internal pressure more consistent throughout varied print speeds, which directly reduces the ooze that would otherwise occur at the start and end of every extrusion move - meaning a well-tuned pressure/linear advance setup can often get away with noticeably less retraction distance than an otherwise identical setup without it.

A More Complete Tuning Approach

If stringing persists after increasing retraction volume to a point where you're now seeing grinding or clicking at the extruder, that's a sign to stop increasing volume and instead look at retraction speed, coasting settings, or enabling pressure/linear advance if your firmware supports it - all of which address the underlying pressure and timing issues that pure retraction volume alone can only partially fix.