Fixing Racking in CoreXY Printers by Adjusting Belt Tension
In 3D printers with CoreXY kinematics, the print head is moved by a gantry driven by two long belts. When the force exerted by these belts is not identical, the assembly experiences diagonal torsion. This phenomenon, known as racking, distorts the geometry of the parts, causing circles to come out oval and dimensions to be incorrect. Identifying and solving this mechanical failure is key to achieving precision 🛠️.
Diagnosing the Source of Racking
The main symptom is a print where circles are not round and squares have unequal diagonals. The cause is usually a difference in tension between the two X-axis belts, which generates a torque that twists the gantry during movement. Before acting, it is essential to confirm that the gantry structure is perfectly square mechanically. A twisted frame will replicate the problem no matter how much you adjust the belts.
Clear Signs of Racking:- Printed parts show diagonal deformations instead of right angles.
- When printing a test circle, an oval or elliptical shape is obtained.
- The gantry movement is not smooth and may produce noises or jolts.
A well-tensioned gantry moves silently and uniformly, without generating asymmetric forces that compromise geometry.
Methods for Precise Tension Adjustment
The goal is to achieve both belts offering the same resistance when stretched. It's not just about tightening, but equalizing. The process requires patience and should be done by turning the tensioner pulleys in very small increments, verifying the result after each change.
Techniques for Equalizing Tension:- Use a Tension Meter: The most objective method. This device measures the belt's vibration frequency, allowing you to match the tone on both sides.
- Guitar Tuner as Reference: An economical alternative. Pluck the belt as if it were a string and use the tuner to match the note it produces on both sides of the gantry.
- Adjust by Ear: For experienced users. You aim for the "zing" when plucking each belt to sound with the same sharp and crisp tone.