Cooling, speeds & acceleration
Print speed isn't a single number — it's the smallest of three different limits: how much molten plastic your hotend can push per second, how much surface area your fan can cool per second, and how fast your motors can change direction without shaking the machine apart. Cura's "100 mm/s" setting means nothing if any of these limits is hit first.
Your printer's real speed limit is the lowest of: max volumetric flow (mm³/s), max acceleration (mm/s²), and cooling capacity. Stock Ender 3 = ~8 mm³/s, ~500 mm/s². Bambu X1 = ~28 mm³/s, ~20 000 mm/s². Run the max volumetric flow test in OrcaSlicer to find yours, then set max volumetric flow in your filament profile and let the slicer cap speed automatically.
Volumetric flow rate — the hotend's limit
Volumetric flow is the volume of melted plastic flowing through the nozzle per second, measured in mm³/s. It's the most fundamental limit because if your hotend can't melt plastic fast enough, the extruder gear simply skips and you get under-extrusion.
Flow rate = layer height × line width × print speed. So at 0.20 layer / 0.45 width / 150 mm/s, flow = 13.5 mm³/s.
Typical hotend limits
| Hotend | Max flow (PLA) | Max flow (PETG/ABS) |
|---|---|---|
| Stock V6 (Ender 3, MK3) | ~10 mm³/s | ~8 mm³/s |
| Volcano / SuperVolcano | ~25 mm³/s | ~20 mm³/s |
| E3D Revo Six | ~12 mm³/s | ~10 mm³/s |
| Bambu X1/P1 stock | ~28 mm³/s | ~22 mm³/s |
| Prusa MK4 / CORE One | ~30 mm³/s | ~25 mm³/s |
| Mosquito Magnum | ~40 mm³/s | ~35 mm³/s |
Filament also matters — PLA flows easier than PETG, which flows easier than ABS. High-flow PLAs (Bambu PLA-HS, Polymaker PolySonic) push flow rates up by 30–50%.
How to measure your real volumetric flow
OrcaSlicer's "Max Volumetric Speed" calibration is the standard. It prints a tower at increasing flow rates; you measure where the print starts under-extruding and set max volumetric speed slightly below that number. Most people are surprised — their printer's real limit is far below what they assumed.
Part cooling — the fan's limit
Part cooling solidifies fresh extrusions so the next layer doesn't melt them or sag onto soft plastic. The faster you print, the more cooling you need to keep up. When you outrun your fan, you see overhangs droop, small-part details slump, and stringing increase.
Fan speed by material
| Material | Layer 1 | Layer 2–3 | After |
|---|---|---|---|
| PLA | 0% | 50% | 100% |
| PETG | 0% | 0–30% | 30–50% |
| ABS / ASA | 0% | 0% | 0–25% |
| TPU | 0% | 30% | 50% |
| Nylon | 0% | 0% | 0–25% |
| PC | 0% | 0% | 0–25% |
When you're cooling-limited
If you increase volumetric flow and overhangs start sagging, you're cooling-limited. Options:
- Improve the fan and duct (CPAP mods, Bambu auxiliary fan, Voron-style fang ducts).
- Slow down small layers — "minimum layer time" forces the printer to spend at least N seconds per layer, giving the previous one time to solidify.
- Print multiple parts simultaneously — gives each layer time to cool before returning.
- Reduce ambient temperature — open the enclosure for PLA prints.
Acceleration — the motors' limit
Acceleration controls how quickly the toolhead changes speed. At 1000 mm/s², going from 0 to 100 mm/s takes 0.1 seconds (a 5 mm distance). Higher acceleration = the printer reaches and holds target speed for more of each move = shorter actual print time, even if the target speed is the same.
Acceleration ceilings by printer class
| Printer | Max acceleration | Effective top speed |
|---|---|---|
| Bedslinger (Ender 3, MK3 stock) | 500–1500 mm/s² | 50–80 mm/s |
| Bedslinger with input shaping (MK3.5) | 2000–4000 mm/s² | 100–150 mm/s |
| CoreXY (Voron, Bambu, MK4) | 8000–20000 mm/s² | 200–500 mm/s |
| Bambu X1 stock | ~20000 mm/s² | ~500 mm/s capable |
Input shaping
Input shaping (or "resonance compensation") measures your printer's natural vibration frequencies and tells the firmware to pre-compensate for them. It lets you run much higher accelerations without ringing/ghosting. Klipper, Marlin 2.1+, Prusa Buddy firmware, and Bambu firmware all support it. Re-run the calibration any time you change major mechanical components (belts, frame, hotend).
Pressure advance
The companion to input shaping. It pre-emptively increases extrusion before corners and decreases after, compensating for melt-zone pressure lag. Without it, you get blobs at corners and gaps after them. Test prints take ~10 minutes; the impact on print quality is substantial.
Jerk (or junction deviation)
Old-school "jerk" is the instantaneous speed change allowed at corners. New-school "junction deviation" is a smarter, geometry-aware version. Both control how much the printer slows for corners. Higher = faster but rougher; lower = smoother but slower. Most users leave the defaults alone (jerk 8–10, junction deviation 0.05–0.1).
Putting it together — practical speed recipes
| Goal | Volumetric flow | Speed | Acceleration |
|---|---|---|---|
| Quality (vase, display) | 5 mm³/s | 40 mm/s | 1000 mm/s² |
| Balanced default | 10 mm³/s | 80 mm/s | 2000 mm/s² |
| Fast functional | 20 mm³/s | 200 mm/s | 8000 mm/s² |
| Bambu/Voron sport mode | 25–30 mm³/s | 300–500 mm/s | 15000–20000 mm/s² |
When fast is wrong
Speed isn't always the goal. Print slow when:
- Small layer area: tall, thin features need time to cool.
- Display-quality finish: slow first 2–3 layers stick better; slow outer perimeters look better.
- Tight tolerances: slow prints have less mechanical artifact.
- Difficult materials: ABS, PC, nylon all benefit from slower print speeds for layer bonding.
- Wet filament: slow can mask wet-filament issues; better to dry the filament.
Related articles
Sources & further reading
- Prusa Knowledge Base — Input shaper and pressure advance
- Klipper docs — Resonance compensation
- Bambu Lab Wiki — Volumetric speed and how it impacts 3D printing