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When i print anything longer than an hour the machine will suddenly make a loud knocking noise and then the filament will stop feeding and ultimately break. When I unload the filament i notice it has notches in it like it is not feeding properly. I have cleaned everything, got a new nozzle and am not sure what to try next.
From your description.... If the hot end has a teflon tube insert that butts up to the top of the nozzle it's likely that the end of it is not cut straight across and does not seat properly up to the nozzle. The end of it could have deteriorated with heat. Either one will allow a build up of melted plastic and cause a blockage which makes the extruder gear chew up the filament. In either case a new teflon insert will help. The best cure is an all metal hot end incorporating a heat break which will stop any heat creep.