Under-extrusion (gaps, thin walls)

Try these in order

Most likely and quickest to check first. Change one thing at a time so you know what fixed it.

1. Partly blocked nozzle

   • Heat the nozzle and push filament through by hand. A thin or curling stream means a partial clog.
   • Do a cold pull, or replace the nozzle.

2. Printing too fast for the hot end

   Every hot end can only melt so much plastic per second. Past that, it can't keep up.

   • Slow down, especially infill, or set a maximum volumetric speed in the slicer (around 10 to 15 mm³/s for a standard hot end).
   • Raise the temperature by 5 to 10 °C if you need the speed.

3. Wrong filament diameter or flow in the slicer

   • Check the filament diameter is set to 1.75 mm (or 2.85 mm for those printers).
   • Measure the filament with callipers in a few places; cheap filament can be undersized.
   • Calibrate the flow rate.

4. Extruder slipping

   • Check the extruder tension and that the drive gear isn't packed with plastic dust.
   • Calibrate extruder steps per mm.

5. Worn or old nozzle

   Brass nozzles wear over months of use, and much faster with glow-in-the-dark, wood or carbon fibre filament. Old nozzles also build up burnt plastic inside, which narrows the hole.

   • Replace the nozzle if prints have slowly got worse and nothing else has changed. Nozzles are cheap.
   • Use a hardened steel nozzle for abrasive filaments.

6. Spool dragging

   • Make sure the spool turns freely and the filament isn't tangled or crossed over on the spool.