Print quality and tuningIntermediate18 min

Dial in your filament: temperature, flow, retraction, pressure advance

Run the calibration tests in the right order and understand each one: a temperature tower with stringing, flow on a top surface, and pressure advance on a corner.

The right order

Each test assumes the one before it is done. Skipping ahead is how people tune around the wrong problem.

1Dry, clean and levelDry the filament, clean the plate and set the first layer from the previous lesson.Look at: A flat, well-stuck first layer.
2TemperaturePrint a temperature tower and pick the step with the best balance of bridges, strings and layer bonding.Look at: Bridges, strings and how shiny or rough each step is.
3Flow ratioPrint a few top-surface plates at different ratios and choose the smoothest.Look at: Gaps on one side, ridges on the other.
4Pressure advancePrint a test with sharp corners at changing speeds and pick the K value that keeps lines even.Look at: Bulging corners or thin gaps after turns.
5RetractionPrint two towers and use the shortest retraction that removes the strings between them.Look at: Fine strings between the towers.
6Check with a real partPrint something you care about. If one symptom remains, go back to the test that matches it.Look at: Corners, small holes and top surfaces.

Temperature and strings

Build a temperature tower and see why the answer is a compromise. Then add retraction and wet filament to see how strings change.

Material

Extruder

Retraction length1.0 mmA common starting point is about 1 mm for this extruder type. Check your printer's profile.The filament is wet (stored open for weeks)Selected step210 °C

Layer bonding100%

Bridging73%

Stringing3%

Best balance: 205 °C190–225 °C

Teaching model with typical temperature windows and the hottest step printed first at the bottom. Real towers vary, so read your own tower's labels and the spool label.

Flow ratio on a top surface

Top surfaces are printed as lines side by side, which makes them the best place to see how much plastic is really coming out.

Flow ratio0.92

Under-extruding

Lines are too narrow to meet, so the surface has gaps. It looks like thin stripes and feels weak.

Gap between lines

0.03 mm

Ridge height

0.00 mm

Change the ratio by a few percent at a time. Print one plate per value, look in good light, and choose the smoothest.

Teaching model. Real plates also depend on the nozzle, speed and temperature.

Pressure advance at corners

Plastic is squeezed through a tiny hole, so pressure in the nozzle lags behind the extruder. That lag is why corners bulge. Pressure advance gives the extruder a head start.

Head speed
Plastic flow at the nozzle

One straight move: speed up, cruise, slow down. At K = 0 the flow trails the speed.

Pressure advance KK = 0.000

K too low

Flow arrives late when speeding up and lingers when slowing down. Expect thin starts and bulges at corners.

Biggest flow error

70%

In real printers the right K depends on the filament, nozzle and hotend. It is found by printing a test and picking the best line, not by calculation.

Teaching model with a single fixed lag of 0.04 s. Real values differ by material and printer.

Real test prints

What the tests above look like on real printers. Compare yours to these.

Close-up of a nozzle tip with a bead of molten plastic hanging from it — Plastic does not stop the instant the pump stops: a drop hangs from the tip. Retraction and a lower temperature are how you keep it from becoming strings.David Elliott · CC BY 2.0 · Wikimedia Commons

Nine printed flow test plates labelled from minus 20 to plus 20, from under-extruded with gaps to over-extruded with ridges — Flow test plates: gaps on the under-extruded side, ridges on the over-extruded side, and a smooth pair in the middle. Pick the smoothest.

A pressure advance line test: rows of lines, each with a different value, with thick and thin spots near the speed changes — Pressure advance line test: the best row has an even line where the speed changes, with no fat start and no thin gap.

A printed temperature tower with labelled steps from 195 to 230 — Temperature tower: each step prints at a different temperature. Pick the step with the cleanest bridges and least stringing.

A top surface printed for a flow rate test with concentric lines — Flow rate test: a smooth, gap-free top surface means the flow ratio is right. Ridges mean too much, gaps mean too little.

A printed box used for pressure advance calibration — Pressure advance test print: check the corners and the seam for bulges or gaps to find the best value.

Two small towers with thin strings between them from a retraction test — Retraction test: thin strings between the towers show retraction is too short. Use the shortest value that removes them.

Check yourself

Pick an answer for each question.

1. On a temperature tower, the hottest steps look best for layer bonding but show thin strings and sagging bridges. What do you pick?

2. Your flow test plate shows ridges and a rough surface. The flow ratio is…

3. Pressure advance helps most at…

4. Thin strings between two towers, and the filament was stored open for weeks. What do you try first?

Sources (6)

Figures such as temperatures and drying times are typical ranges. Always check the label on your own spool and your printer manufacturer's guidance.