Belts look simple, but on CoreXY, Cartesian and many Delta printers they directly determine how motor motion reaches the axis. Too little tension can add compliance, imprecise direction changes and visible ghosting. Too much is also wrong: bearings, motor shafts and belts carry higher load, and extra vibration is possible.
GT2 and GT1.5: what does the number mean?
The number refers to tooth pitch, the tooth-to-tooth spacing. GT2 with a 2.0 mm pitch is very common in 3D printers. Synchronous-belt manufacturers such as Gates likewise define belt systems by pitch and tooth geometry and rely on correct engagement with matching sprockets.
| GT2 | GT1.5 | |
|---|---|---|
| Pitch | 2.0 mm | 1.5 mm |
| Typical role | widespread, mature ecosystem | finer periodic excitation / smaller tooth pitch |
| Compatibility | matched 2 mm drive system | matched 1.5 mm drive system |
| Upgrade? | not a belt-only swap: pulleys, geometry and calibration may also be affected | |
Why Prusa moved to GT1.5 in 2026
This matters now because Prusa introduced GT1.5 belts across its refreshed product family. For the CORE One+ (Gen 2), Prusa explicitly says the new belts reduce fine repeating patterns on smooth surfaces. Firmware support for the current CORE One models also arrived in August 2026.
That is a useful real-world example of why finer pitch can matter, but it does not mean an arbitrary GT2 printer becomes better by swapping belts. The complete drive must be designed around the new pitch.
How belts influence ghosting and repeating surface patterns
Ringing/ghosting appears when a mechanical system continues to oscillate after a rapid direction change. Belts are only one part of the chain: frame stiffness, toolhead mass, pulley runout, bearings, motors, acceleration and resonance compensation all contribute.
- Too loose: force transfer becomes less defined and compliance can increase.
- Too tight: bearing and shaft loads rise, friction increases and new resonances are possible.
- Unequal tension: especially on CoreXY machines, gantry alignment and motion resistance can suffer.
- Wrong pitch or pulley: poor tooth engagement, wear, noise and positional errors.
Why tensioning “by feel” is hard to reproduce
Resonance frequency is more repeatable than a subjective finger test. A defined free belt span is plucked and its fundamental frequency is measured with an app or meter.
An idealized belt span behaves approximately like a string, so frequency depends on tension, free span and linear mass. That is exactly why there is no universal frequency for every printer.
Concrete manufacturer example: Prusa CORE One family
Prusa’s current Belt Tuning Wizard uses controlled belt excitation and specifies 85–95 Hz for the CORE One family. Prusa also states that up to 8 Hz difference between the two belts can be acceptable, and asks users to check gantry alignment before tuning.
This is what a trustworthy target looks like: model- and method-specific. It should not be copied into an unrelated Voron, Bambu, Creality or Sovol setup.
How to measure belt frequency consistently
- Open the manufacturer procedure. Axis position and measurement location matter.
- Use the same free span every time. Different span length means different frequency.
- Pluck gently and consistently.
- Repeat the measurement. One outlier is not calibration.
- Adjust in small steps. Treat paired CoreXY tensioners evenly when required.
- Move the axis and remeasure. Let the belt settle.
- Verify with a print. Frequency is not a substitute for actual surface quality.
Why identical Hz is not always the only goal
Similar tension makes sense on symmetric systems, but construction matters. Prusa’s current wizard explicitly allows some difference. Forcing both belts to exactly the same number while the gantry is out of square can hide the actual problem.
Typical signs of too little tension
- more visible oscillation after corners,
- poor repeatability or positional compliance,
- higher risk of tooth skipping under load,
- difficulty keeping a CoreXY gantry square,
- frequency clearly below the manufacturer target.
Typical signs of too much tension
- more bearing or motor noise,
- unnecessarily heavy axis movement,
- greater load on motor shafts, bearings and idlers,
- faster belt/bearing wear,
- frequency clearly above the manufacturer target.
Is GT1.5 a drop-in upgrade for a GT2 printer?
No. Changing pitch changes drive geometry. Matching pulleys are mandatory; depending on firmware and kinematics, rotation distance/steps, homing, routing and calibration can also be affected. Only treat it as an upgrade when a technically validated conversion exists for that specific printer.
Belts or Input Shaper?
Mechanics and resonance compensation complement each other. Input Shaper can reduce known resonances during acceleration, but it should not hide a loose belt, eccentric pulley or failing bearing. Get the mechanics reproducible first, then tune resonance compensation and motion limits.
Practical checklist
- Confirm belt pitch and pulley compatibility.
- Inspect belt teeth and edges for damage.
- Check idlers/pulleys for smooth rotation and secure mounting.
- Square the gantry or axis geometry.
- Find the manufacturer target and measurement position.
- Measure repeatedly and adjust gradually.
- Verify with a ghosting test or a real smooth-wall print.
Conclusion
GT1.5 is technically interesting because smaller pitch can shift periodic excitation to a finer pattern, and Prusa’s current machines show manufacturers using that lever specifically for cleaner smooth surfaces. For an existing printer, however, correct tension of the designed belt system usually matters more than a speculative conversion. Frequency measurement makes that adjustment repeatable rather than subjective.
Sources & documentation
- Prusa CORE One+ – GT1.5 Gen 2 update
- Prusa – 2026 product upgrade / repeating surface patterns
- Prusa Knowledge Base – Belt Tuning Wizard
- Prusa CORE One+ firmware changelog – GT1.5 support
- Gates PowerGrip GT3 – 2 mm pitch example
Research status: September 2, 2026. Manufacturer targets can change with printer revision, firmware and measurement method.
Frequently asked questions
Is GT1.5 always better than GT2?
No. GT1.5 has a smaller pitch and can make periodic surface patterns finer, but it requires a completely matched drive system.
What belt frequency is correct for a 3D printer?
There is no universal Hz target. Use the printer manufacturer target for the specified measurement position and belt configuration.
Can an over-tight belt cause ghosting?
Yes. Excess tension can increase bearing and motor-shaft load, friction and additional resonances.
Can I simply replace GT2 with GT1.5?
No. Belt pitch and pulleys must match, and calibration, firmware parameters and belt routing may also be affected.
What does belt frequency say about tension?
For the same belt and free span, frequency rises with tension. Without known linear mass and span length it is primarily a repeatable comparison value rather than an absolute Newton measurement.
