Milling the chimney slot

it relates to the extend an existing chimney.
The tool is round left in the chimney with rope.
By turning the hydraulic rotating the cutter and works by centrifugal force the knife out.
The tool is now pulled back and extends the chimney.
My question: does anybody know a better solution, or what can be improved?
The material is removed which is Schamot or concrete .....

Thanks for any hint, Leo Thonhofer

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