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grambell789 t1_je5sauv wrote

I'm more curious about the milling process. I've seen the machines and it just looks like a big rotor with knives - hammers on it. how to they deactivate those when that part of the rotor gets near the manhole, is there some kind of ferrous sensor? I never see a manhole battered so they must be pretty effecicent at detecting and avoiding them.