Max Volumetric Flow Test for PrusaSlicer – Hotend Flow Limit | HexCalibr

A hex column and a long wedge that find how much plastic your hotend can melt per second. It opens in PrusaSlicer with the speed steps already set: no profile edits, a guided reading and a scorecard that suggests the value.

Step-by-step guide

Photos, the hotend table, firmware limits, the scorecard and troubleshooting: hexcalibr.ui4.eu/max-flow.html
Scorecard: hexcalibr.ui4.eu/max-flow-scorecard.html

What it does

The wedge is printed in bands, each one faster than the one below. The number on the hex column beside each band is its flow in mm³/s, measured on the two long straights. Read the straights, not the column: find the last clean band there and set your filament's Max volumetric speed a little below it. PrusaSlicer then never asks the hotend for more plastic than it can melt.

Why HexCalibr

• No profile edits. Open the project and your profiles stay as they are. A speed factor (M220) at each band makes the printer run faster; the slicer sees a slow, steady print and never slows it down.

• Guided reading. The guide shows how a starving wall looks (matte, thin, gaps), how to tell a heater limit from a melt limit, and a "my hotend → which file" table.

• Scorecard. Mark each band on the online card; it suggests the value to type into your filament profile.

Which file to download

One file per hotend tier and nozzle, for every firmware (Klipper, Marlin, Prusa, RepRapFirmware).

• standard (E3D V6, Revo, Prusa Nextruder, brass 0.4 nozzles): standard-0.4 (4–32 mm³/s) · standard-0.6 (6–36)

• hf (high-flow hotends; also the first run on a UHF hotend with a 0.4 nozzle): hf-0.4 (10–50) · hf-0.6 (12–60)

• uhf (Rapido UHF, Dragon UHF, Goliath, Chube): uhf-0.4 (16–64) · uhf-0.6 and uhf-0.8 (28–100)

• extreme (Magnum+, SuperVolcano, Rapido X): extreme-0.8 and extreme-1.0 (30–180)

• flex (TPU and other flexible filaments, any hotend): flex-0.4 (1–10 mm³/s)

• IDEX: hf-0.4, uhf-0.4 and flex-0.4 also come as T0 / T1, one per toolhead

Quick steps

1. Download the single .3mf for your hotend and nozzle (not "Download all" as a ZIP).

2. In PrusaSlicer 2.9 use File › Open project, never Import.

3. In the preview, check the markers on the layer slider and that your firmware's max speed and acceleration are high enough (the guide has the table).

4. Print at the temperature from the temperature tower. Listen for extruder clicks and watch the hotend temperature on the top bands.

5. Find the last clean band on the scorecard and set your filament's Max volumetric speed to about 85 % of it.

If you cancel the print, send M220 S100 from the printer console: the file speeds the printer up band by band, and the top of the tower sets it back.

A real result

PETG on a RatRig V-Core 4 IDEX (Rapido UHF, Orbiter 2.5, 0.4 nozzle), hf-0.4 file: the last clean band was 30 mm³/s, so I set 25 mm³/s. The heater held within ±0.8 °C and the extruder never clicked: the limit was the hotend's melt capacity, not the extruder.

Clear TPU 87A on the same printer, flex-0.4 file: band 3 was the last clean one, a crosshatch texture started in band 4 and the wall collapsed from band 7. I set 2.5 mm³/s.

IDEX and multi-tool

Test each toolhead on its own with the T0 / T1 files: two hotends of the same model can still melt differently.

Share your Make

Printed it? Post a Make with a photo of your last clean and first failed band, and say which hotend, nozzle, temperature and value you ended up with. Makes help other people with the same hotend.

Watch the trailer

License and credits

CC BY-SA 4.0. HexCalibr by Matteo Beretta. If you share or remix it, credit "HexCalibr by Matteo Beretta", link back to this page, and keep the same license. The HexCalibr name and logo are not covered by the license: please give modified versions a different name. The official, always-updated files are on this page. Original design; the methods owe a lot to Ellis' Print Tuning Guide and CNC Kitchen (see License and credits).

Not affiliated with or endorsed by Prusa Research, Rat Rig, E3D, Phaetus, Slice Engineering, Bondtech or any other brand named here. All trademarks belong to their owners.

Version 1.3 · made for PrusaSlicer 2.9 (2.7 minimum).

🇮🇹 Italiano

Una colonna esagonale e un lungo cuneo stampati sempre più veloci, fascia dopo fascia, per trovare quanta plastica al secondo riesce a fondere il tuo hotend. Si apre in PrusaSlicer con i passi di velocità già impostati, senza modificare i profili. Scegli il file del tuo hotend e del tuo ugello, aprilo con File › Apri progetto, stampa e valuta le fasce sulla scheda punteggio. Se annulli la stampa, invia M220 S100. Guida completa in italiano: hexcalibr.ui4.eu/it/max-flow.html