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Belt Tensioning Guide

On a CoreXY printer, correct and consistent belt tension is one of the most critical factors for achieving high print quality. * Loose belts will cause "ghosting" or "ringing" artifacts and can lead to poor dimensional accuracy. * Overly tight belts will put excessive stress on the motor bearings and idlers, leading to premature wear and potential motion issues.

The most accurate and repeatable way to set belt tension is by measuring the frequency of the belt's vibration, much like tuning a guitar string. You will need a smartphone with a spectrum analyzer app (such as "Sound Analyser" on Android or "Decibel X" on iOS).

A/B (CoreXY) Belts

  1. Position Toolhead: Move the toolhead to the center of the X-axis. Move the gantry so the toolhead is approximately 150mm away from the rear idlers.
  2. Measure Frequency: Hold your phone's microphone close to the longest, top span of the A-belt. Gently "pluck" the belt with your finger. The analyzer app should show a peak frequency.
  3. Adjust Tension: Adjust the A-belt's tensioner until the peak frequency is approximately 110 Hz.
  4. Repeat: Repeat the exact same process for the B-belt. It is crucial that both belts are tensioned to the same frequency.

Using a phone app to measure belt tension frequency Using a phone app to measure belt tension frequency

A smartphone with a frequency analyzer app held close to a 3D printer belt that is being plucked by a finger. The app displays a clear frequency peak.

Z-Axis Belts

  1. Position Gantry: Move the gantry to roughly the middle of its Z-axis travel.
  2. Measure Frequency: Pluck one of the vertical Z-belts and measure its frequency.
  3. Adjust Tension: Adjust the Z-belt's tensioner until the frequency is approximately 140 Hz.
  4. Repeat: Repeat for the other three Z-belts, ensuring they are all tensioned as equally as possible.

The Qualitative Method (Quick Check)

For quick weekly checks, you don't need to use the frequency method every time. Simply pluck the belts and get a feel for their tension. They should be taut and produce a low, audible tone. The key is to ensure they feel consistent with each other and haven't become noticeably loose over time.