Belts, tension and layer shifts

When a print comes out with ghosting around every corner, or the top half is offset from the bottom, the cause is almost always mechanical rather than in the slicer. Belts are the first place to look and the cheapest thing to fix.

Symptoms and what they mean

• Ringing / ghosting — repeated ripples fanning out after a sharp corner. Usually loose belts, sometimes a wobbly frame or simply printing too fast.
• Layer shift — the print jumps sideways and continues from the wrong place. A skipped step: something obstructed the head, a belt slipped a tooth, or a pulley grub screw came loose.
• Rounded corners and inconsistent dimensions — slack belts letting the head lag behind commanded position.

Tensioning by feel

There is no torque figure, but the standard test is reliable: pluck the belt like a guitar string. It should produce a clear, low note — a proper pitch rather than a dull flap. Both axes should sound similar. If you can twist a belt more than about 90 degrees between finger and thumb mid-span, it is too loose.

Too tight is a real failure mode, not just a theoretical one: excessive tension loads the stepper bearings and pulls the frame out of square. Tight enough to ring, not tight enough to strain.

Many printers have a thumbscrew tensioner. If yours does not, printing one is a common first upgrade — and if the belt has stretched beyond adjustment, replace it. GT2 belt is inexpensive by the metre; steel-reinforced belt stretches far less than the plain fibreglass sort.

Check the pulleys too

A grub screw backing off a motor pulley produces symptoms identical to a slipping belt and is often missed. Make sure the screw seats on the flat of the motor shaft, not on the round, and check both axes. This single check resolves a lot of intermittent layer shifts.

Also spin the idler pulleys by hand — they should turn freely and quietly. A seized idler drags the belt and wears it flat.

Other causes of a layer shift

• The head hitting the print. A curled corner or blob catches the nozzle. This is why warping matters beyond looks.
• Printing too fast for the machine — particularly acceleration on a bed-slinger carrying a heavy plate.
• Stepper driver overheating, causing skipped steps late in a print.
• Something obstructing motion — a cable snagging, or a spool binding on its holder. See spool holders.

The maintenance that prevents it

Check belt tension every few months, keep the linear rails or rods lightly lubricated, keep the frame bolts tight, and do not let dust build up on smooth rods. Ten minutes occasionally, and mostly with tools you already own.