Ghosting

Ghosting appears as small vertical vibrations that are consistent in the travel height and rapidly subside when traveling in the X or Y direction. They usually appear on corners.

What's Happening?

Ghosting generally appears as an artifact when the printer suddenly changes direction, creating a large acceleration in a different direction. The result is that the printer must decelerate from its previous direction.

Fixing

There are a number of quick-fixes.

• Ensure that CoreXY belt tension is even. Belts should be within 1 [Hz] of each other when plucked from the same relative location. Mismatched tension can cause the XY gantry to bind, rather than move freely, creating a buildup of force required to move the tool head. You can measure the frequency of the belt pluck with a guitar tuning smartphone app.
• Tension both belts to at least 60[Hz]. Increasing belt tension increases the preload, making the input-to-output loop stiffer, and thus, making it harder for the belts to stretch when subjected to external forces (such as changes in the tool head direction). Note that the

Slightly more advanced fixes:

• Lower the travel acceleration and jerk settings. 2000[mm/sec] XY acceleration is a modest number for printing applications.

Much more advanced fixes include:

• Enable, and calibrate *Input Shaping.* Input Shaping is a feedforward vibration correction technique that is present on both Klipper and RepRap Firmware. A properly tuned machine can yield drastic ghosting reduction. See more details on this concept in the Klipper docs.
• Install 9mm tall belts instead of the default 6mm tall belts. 9mm belts stretch about 50% as much as 6mm belts, making the overall input-to-output loop stifer.