Rotate transform ruins lines

Hi trying to save time animating an arm in a different layer , in each layers frame i
rotate it by little. But each rotation make the outline even more ugly and broken? How
should approach that?

This is an unavoidable issue with rotating pixel art. It cannot be rotated perfectly, except in increments of 90 degrees.

If you want to mitigate some of the damage, keep your original art available and make each new rotation from it instead of the previous rotated version. This will prevent the errors from compounding, at least.