3D printing glossary

Definitions

E-steps

E-steps (extruder steps per millimetre) tell firmware how many motor pulses equal 1 mm of filament. If you command 100 mm and measure 95 mm at the drive, new e-steps = old × 100 / 95. Calibrate after a new hotend, gear, or Bowden tube. Direct-drive and Bowden use the same formula; only the starting e-steps differ.

Volumetric flow

Volumetric flow Q = layer height × line width × print speed. Units are mm³/s. A typical brass 0.4 mm hotend maxes out around 8–15 mm³/s; high-flow volcano-style heaters go higher. If Q exceeds the hotend, you get under-extrusion even when e-steps are perfect. Max speed at a given layer is Q_max / (height × width).

Layer height

Layer height is the thickness of each deposited (FDM) or cured (SLA) slice. On FDM a common rule is 25–80% of nozzle diameter: 0.2 mm layers with a 0.4 mm nozzle are typical. On resin, thinner layers need less exposure per slice but more slices, so total time is not linear. Changing layer height changes volumetric flow, cost and surface finish together.

Filament density

Filament density is mass per cubic centimetre of the solid plastic. Length-to-weight uses the cylinder volume πr²L times density. PLA is typically 1.24 g/cm³, PETG 1.27, ABS 1.04, TPU around 1.21. Spool labels quote 1 kg of plastic, not 1 km of length — 330 m of 1.75 mm PLA is roughly a kilogram. Colour and foam additives shift density a few percent.

Rotation distance

Rotation distance is Klipper’s millimetres of motion per motor revolution. On an extruder it is millimetres of filament per gear revolution. If you request 100 mm and measure 95 mm, the rotation distance is too large: new = old × 95 / 100. It is the inverse of Marlin e-steps: RD = (full steps × microsteps × gear ratio) / e-steps. Calibrate after a new hob, gear or Bowden tube.

Input shaper

Input shaping (Klipper, some Marlin builds) measures the printer’s resonant frequency with an accelerometer and cancels ringing by splitting each move. Higher frequency usually allows higher acceleration. Heavier shapers (EI, 2HUMP EI) cancel more ringing but smooth more, so recommended accel is lower than ZV at the same Hertz. The calculator is a starting cap, not a substitute for resonance testing.

Heat-set insert

Heat-set inserts are knurled brass threads pressed into thermoplastic with a soldering iron or press. The pilot hole is typically 0.3–0.5 mm under the insert’s outer diameter so plastic reflows into the knurl. Depth is insert length plus a little clearance so you do not punch through a thin boss. PLA wants a cooler iron than ABS or nylon. Oversized holes spin; undersized holes bulge the boss.

Print-in-place

Print-in-place (PIP) mechanisms — hinges, nuts on screws, chain links — come off the plate already assembled. They need a designed gap so the layers do not fuse. A practical clearance is twice the printer’s measured dimensional error plus a fit extra: tight/press, sliding, or loose. Z is usually worse than XY because of layer lines and elephant’s foot. Test a coupon before you commit a 12-hour print.

Line width

Line width (extrusion width) is how wide each deposited trace is. It is often 100–120% of nozzle diameter and can go to ~150% on thick infill. Perimeter walls that are not integer multiples of line width leave a thin leftover extrusion that under-extrudes or overfills. Round the wall to n × width, or change width so n × width hits the CAD thickness.

Exposure time

Exposure time is how long the UV LCD cures each resin slice. Mono screens are several times faster than older RGB panels at the same layer height. A first-order scale is t_new = t_old × (h_new / h_old) × (screen_new / screen_old). Always print an exposure calibration matrix after a resin, screen or firmware change — the formula is a starting guess, not a certified cure.

Specific gravity

Specific gravity (SG) is density relative to water at 4 °C, so 1.10 means 1.10 g per millilitre. Slicers report resin volume in ml; bottle prices are per kilogram. Grams = ml × SG. Standard photopolymer is often 1.08–1.12, tough and ABS-like a little higher, some washable and castable resins higher still. Temperature and pigment shift SG slightly.

Microstepping

A 1.8° motor has 200 full steps per revolution. 16× microstepping commands 3200 pulses per rev. Linear resolution along a lead screw is lead / (200 × microstep). TR8×8 at 16× is 8 / 3200 = 0.0025 mm per pulse on paper. Extra microstepping smooths motion but does not multiply holding torque; mechanical pitch and belt slack usually dominate Z banding before the step size does.