I've made a project to play with 3x3 convolution filters as described (filters are implemented as a hyperized sum of the whole shifted arrays)
Below is a Stage image with 3 segments
Orig > Gaussian > Sobel Y (edge detection) > Sobel Y result
Orig - original record groove image
Orig > Sobel Y result
Even if this is not directly applicable to the problem maybe can be used to further experiments (at least converting to grayscale and threshold cut).
BTW.It seems that there are still some material shavings extruded at the edge of the groove.
can be used this way
