Reference · the course vocabulary

Glossary

The canonical language of this course. Mirrors GLOSSARY.md — edit the Markdown first, then mirror it here.

AThe machine

bedslinger

A printer whose bed moves on the Y axis while the toolhead moves on X and Z. The MK3S and MK4S are bedslingers. The moving mass grows with the part, which is why acceleration and external-perimeter speed are the first things to give. Avoid: "i3-style" — that describes the frame, not the constraint that matters.

CoreXY

A motion system where two fixed motors drive both X and Y through a crossed belt path, so only the lightweight toolhead accelerates. The Core One is CoreXY. Higher usable acceleration, but gantry squareness now depends on the two belts being tensioned equally.

toolhead

The moving assembly that carries the hotend and, on direct-drive printers, the extruder. Everything about print quality is decided by where the toolhead is and how much plastic is coming out of it at that instant.

hotend

The heated end of the machine: heater block, thermistor, nozzle, and above them a heatbreak and heatsink. Its job is to hold a controlled melt zone. Its capacity — how fast it can melt plastic — sets the machine's real speed ceiling, expressed as max volumetric speed.

heatbreak

The thin-walled section between heatsink and heater block that keeps the melt zone short and well-defined. When it fails to do that, softened filament creeps upward and jams — heat creep.

extruder

The geared motor assembly that pushes filament into the hotend. On all three printers in this fleet it is direct drive — mounted on the toolhead, a few centimetres of filament path to the melt zone. Prusa's MK4-family extruder is the Nextruder; the MK3S uses a Bondtech-style dual-drive extruder. Avoid: using "extruder" to mean the whole toolhead.

build plate

The heated bed plus its removable spring-steel sheet. The sheet's texture (smooth PEI, satin, textured) changes both adhesion and the first-layer offset you need.

BWhat comes out of the nozzle

extrusion width

How wide a single deposited line is, set by the slicer — not simply the nozzle diameter. Typically ~0.45 mm for a 0.4 mm nozzle. One of the three terms in the extrusion equation.

layer height

The vertical distance the Z axis rises between layers, and therefore the height of every extruded line. The second term in the extrusion equation.

extrusion equation

volumetric flow (mm³/s) = layer height × extrusion width × print speed. The one piece of arithmetic the whole course rests on: it converts a speed you set into a demand on the hotend, and it is why raising speed without checking max volumetric speed silently under-extrudes.

volumetric flow rate

Plastic delivered per second, in mm³/s. The honest unit for "how fast is this printing", because it is independent of layer height and width — unlike mm/s.

max volumetric speed (MVS)

A per-filament ceiling in mm³/s that clamps every speed in the profile. It represents what the hotend can actually melt. Set correctly it is a safety net; left at a default it is the reason fast prints come out matte and weak. Avoid: "flow rate" — ambiguous, that also names extrusion multiplier.

extrusion multiplier (EM)

A per-filament scalar on how much filament is pushed for a given commanded volume, where 1.0 = 100 %. Corrects for real filament diameter and material behaviour. Total flow is firmware M221 × slicer EM, and the two are independent — changing one does not update the other. Avoid: "flow", "flow rate" — used for both this and MVS in the wild.

retraction

Pulling filament back a short distance before a travel move, so the nozzle stops oozing. A printer setting whose correct value is material-dependent, so it is overridden per filament.

dynamic overhang speed

A print setting that slows extrusion in proportion to how little of it overlaps the previous layer, so overhangs get the cooling time they need without slowing the whole print. Shaped by four control points pairing an overlap percentage with a speed, linearly interpolated between. Shares its vocabulary with dynamic fan speeds, and the two should agree.

AutoSpeed

What happens when a per-feature speed is set to 0: max volumetric speed stops being a brake and becomes the basis for calculating that feature's speed. A legitimate mode, and a bad place to arrive by accident — clearing a speed field is enough to trigger it. Avoid: reading 0 as "disabled" — in the MVS field, 0 means no limit.

CCompensating for physics

Linear Advance (LA)

The Marlin feature that varies extruder speed ahead of acceleration changes, so pressure in the melt zone stays matched to the commanded flow. On the MK3S it is set with M900 K<value>; typical values for a 0.4 mm nozzle are small, around 0.02–0.08.

Pressure Advance (PA)

The Buddy-firmware equivalent of Linear Advance, used on the MK4 family and Core One from firmware 5.0.0. Set with M572 S<value>, which also takes D (extruder number) and W (the velocity-averaging window, default 0.04 s). A value is never transferable between the MK3S and the Buddy machines — and the reason is subtler than a unit mismatch. Buddy converts a legacy M900 command 1:1 into a PA value and applies whichever advance command came last, so a copied number is accepted silently. What differs is the correct value: it characterises that machine's extruder and melt zone, not the material. Prusa's MK3S defaults for a 0.4 nozzle are PLA 0.05 / PETG 0.08, while the MK4S family ships nearer 0.03–0.04 for PLA. Roughly double, for the same plastic.

Input Shaper (IS)

A Buddy-firmware feature that cancels the frame resonances which cause ghosting, letting the printer run much higher acceleration for the same surface quality. Present on Core One, MK4/S and MK3.9/3.5. It compensates for resonance; it does not fix a loose belt, so belts come first.

ghosting

Faint repeated echoes of a feature on the surface downstream of it, caused by the frame or gantry ringing after a direction change. Symptom of resonance, loose belts, or too much acceleration. Avoid: "ringing" — same thing; this course says ghosting.

DGetting the machine honest

selftest

The printer's own guided hardware check — motors, endstops, fans, heaters, and on the MK4 family the loadcell. It is the floor: nothing measured afterwards means anything if the selftest fails.

belt tension

How tightly the X and Y belts are strung. Too loose gives ghosting, layer shifts and out-of-round circles; too tight loads the bearings and skews axis-length measurements. Measured as a belt-status number on the MK3S (X ≈ 250, Y ≈ 275) and as a frequency in Hz on the Core One (90–98 Hz, the two belts within 8 Hz of each other).

PINDA

The inductive probe on the MK3S that finds the steel sheet. It senses metal, not the nozzle, so its reading drifts with temperature and the nozzle-to-sheet distance must be set separately by Live Adjust Z.

loadcell

The force sensor in the MK4-family heatsink that detects the nozzle physically touching the sheet. Because it senses the nozzle itself, first-layer height is measured automatically before every print and no manual Live Adjust Z is needed.

Live Adjust Z

The stored nozzle-to-sheet offset for the first layer, adjusted while the first layer prints. Typical values run from −1.500 to −0.200; turning the knob counter-clockwise moves the nozzle closer. On loadcell machines it exists only as a temporary nudge — the persistent value is the printer's Z offset.

mesh bed levelling

Probing a grid of points across the sheet before a print and warping the first layer to match, so a bed that isn't perfectly flat still gets an even first layer. It compensates for shape, not for height — height is Live Adjust Z.

PID tuning

Calibrating the control loop that holds a heater at target. Worth running when the nozzle temperature wanders by roughly ±5 °C; a bigger swing than that is a hardware fault, not a tuning problem. The Buddy-firmware equivalent on the MK4 family is thermal model calibration.

skew

The deviation of the machine's X and Y axes from a true right angle, measured by the MK3S's XYZ calibration and corrected in firmware. Uncorrected skew turns squares into parallelograms no profile setting can fix.

EMaterials

glass transition temperature (Tg)

The temperature at which a solid polymer stops being rigid and starts to soften — well below its melting point. Tg is why a PLA part left in a hot car deforms, and why the Core One's enclosure has to be vented for PLA.

hygroscopic

Readily absorbing moisture from the air. PETG is hygroscopic and TPU badly so. Absorbed water flashes to steam in the melt zone, producing popping, stringing and weak layers — and it invalidates every temperature, flow and retraction measurement taken with that spool.

drying

Baking moisture out of filament before use. Not an optimisation in a humid climate — a prerequisite, because a wet spool makes the whole calibration chain measure the water rather than the plastic.

FProfiles

system profile

A filament, print or printer preset shipped by Prusa and bound to a printer family. It carries the printer-specific conditional G-code and receives vendor updates. You start from one and Save as — overwriting it loses both.

compatible printers condition

An expression on a preset (Filament Settings → Dependencies) that decides which printers the preset appears for. If it evaluates false the preset is hidden entirely, with no message — which is what makes it a guard rather than a warning. Written against printer_model and nozzle_diameter. Avoid: "printer filter".

after layer change G-code

A block in Printer Settings → Custom G-code that runs at every layer transition, and the mechanism behind every stepped test in Phase 2 — temperature towers, advance towers, flow ramps. It lives in the printer profile, so it applies to every filament and every model sliced on that machine until you delete it. Deleting it is part of the test, not an afterthought.

filament overrides

The section of Filament Settings that lets a filament preset override values structurally belonging to the printer profile — retraction above all. Each value has a tickbox: unticked inherits from the printer, ticked freezes at what you set. Override what the material genuinely changes, and leave the rest inheriting.

config bundle

A single .ini holding every custom print, filament and printer preset in the current PrusaSlicer version. Exported via File → Export → Export Config Bundle. It is the only backup of your measured values, and being a text file it is diffable in version control.

elephant foot compensation

A print setting that shrinks the first layer's perimeters to counter the bulge caused by squishing it against the bed. Around 0.2 mm suits a 0.4 mm nozzle. A top-level setting — influenced by every other calibration, so it is tuned last, at validation.

validation set

The three prints and five acceptance criteria that decide whether a profile is finished: a dimensional test, a combined overhang/bridge/stringing test, and a real part of your own. Each failing criterion names the calibration order step to return to.

GMethod

calibration order

The fixed dependency chain this course follows: machine → temperature → extrusion multiplier → pressure/linear advance → retraction → cooling → max volumetric speed → speeds and accelerations. Each step assumes everything before it is fixed, so changing an earlier one invalidates every later measurement.

temperature tower

A single tall print whose nozzle temperature steps down by 5 °C every 10 mm, giving you every candidate temperature on one object, one spool, one machine, one session. The first measurement of Phase 2. Judge the middle of each band, never the boundary — M104 doesn't wait for the nozzle to arrive.

snap test

Breaking a printed band across its layer lines to see how it fails. A granular, ragged tear through the plastic means the layers fused; a clean, flat split along a layer line means they merely stacked. It outranks every visible criterion, because the failure it detects is invisible from the outside.

one-variable rule

Change exactly one thing between two test prints. Two changes give you a result you cannot attribute, which is worse than no result because it feels like data.

tuning log

The written record of what was measured, on which machine, with which spool, on what date. Without it the fleet drifts and nobody can say which number came from a measurement and which from a guess.

Glossary · all lessons · The Calibration Card