On a CoreXY printer, the belts do more than move the print head. They are the motion system. Two belts working together position the toolhead on every move, which means belt tension touches everything: dimensional accuracy, surface finish, and how fast you can push the machine before quality falls apart. Getting tension right is one of the cheapest speed upgrades you can make.
Why tension matters more on CoreXY
A bed-slinger moves one axis per motor. CoreXY is different. Both motors drive both axes through a crossed belt path, so any slack or uneven tension shows up as skewed geometry and ringing on all your prints. Too loose and the belts bounce, rounding corners and ghosting details. Too tight and you load the motor bearings and idlers, which adds friction, heat, and wear. The goal is even tension on both belts, firm but not strung like a guitar.
How to check your current tension
Start with the pluck test. With the printer off, pluck each belt like a string. You want a low, clear tone, roughly the same pitch on both belts. A dull thud means too loose. A high ping means too tight. This is a rough check, not a measurement, but it catches the common problem: one belt noticeably tighter than the other.
For a real number, use a tension meter or a phone app that reads belt vibration frequency. Most builders aim for the range their printer's community recommends, commonly somewhere that produces a clean tone without straining the idlers. Whatever method you use, the key comparison is belt to belt. Matched tension matters more than hitting an exact number.
Tuning procedure
- Home the printer and power it off so the motors hold no position.
- Center the toolhead by hand so both belts have equal working length.
- Loosen the belt anchor or tensioner screws on the tighter side first.
- Adjust in small increments, plucking both belts after each change.
- When the pitch matches, move the toolhead to all four corners by hand. It should glide with even resistance everywhere.
- Run a test print with sharp corners, like a 20mm calibration cube, and check for ringing.
Reading the test print
Ringing, those faint ripples trailing off sharp corners, usually means the belts are too loose or your acceleration is too high for the current tension. Skewed cubes, where the sides lean, point to uneven tension between the two belts. One side of the print looking worse than the other is the classic symptom. If the cube is clean but the motors run hot or you hear bearing noise, back the tension off a touch.
Speed, acceleration, and tension together
Tension sets the ceiling for how hard you can push acceleration. A well-tensioned CoreXY can run noticeably higher acceleration before ringing appears, which is where the real speed gains come from. Most of your print time is spent accelerating and decelerating, not cruising at top speed. So the practical path is: tune the belts first, then raise acceleration in steps until ringing returns, then back off slightly. That combination is worth more than any top-speed number in your slicer.
Maintenance
Belts stretch slightly over the first weeks of use and then settle. Check tension monthly if you print often, and always recheck after any crash or after working on the gantry. When a belt no longer holds tension or shows fraying at the teeth, replace it. Belts are cheap. Chasing print defects caused by a worn belt is not.
The bottom line: matched, moderate tension on both belts, verified by pitch and by a test cube, then tune acceleration to match. That is the whole job, and it pays off on every print you run afterward.
Related Guides
- Stepper Motor Damping for CoreXY Resonance Drops: CoreXY printers are fast because both motors work together to move the toolhead, but that same coupled motion makes them resonance-prone: the long
- Dual Gear Extruder Tension Tuning for Flex TPU: Flexible TPU filament is the 3D printing material that behaves like a wet noodle: it buckles, binds, and jams in extruders designed for rigid
- Tuning Input Shaper Frequencies via Accelerometer: Input shaping cancels the vibrations that cause ringing and ghosting on 3D prints, but it only works when the shaper is tuned to the printer's actual
- Input Shaping Accelerometer Mounting on Toolheads: Input shaping cancels the vibrations that cause ringing and ghosting in 3D prints, but it can only cancel what it can measure. The accelerometer that