Can bodymaker diagnostics

A method of detecting defects in the sidewalls of can bodies within a can body maker comprising: obtaining output signals from eddy current sensor(s) 500A-D arranged around the ram axis outside of, and adjacent to, an exit end of the tool pack; processing the output signals to detect passage of the can sidewalls past the sensor(s); determining the heights or thicknesses of can sidewalls; and analysing the determined measurements to identify can body sidewall defects or deterioration. Preferably, the sensor(s) are mounted within a stripper housing 502. Preferably the output signals are correlated with ram position data obtained from an encoder. Preferably, analysing the measurements comprises determining whether they within a pre-determined range with a width of less than 2mm. Preferably, on detecting a defect, operating parameters of the bodymaker or production line are adjusted to mitigate the occurrence of defects. The parameters may include rate of can production; operating temperature; coolant or lubricant supply rate or the domer position. Apparatus, systems, a computer device, a computer program, a method of operating a can body maker are also claimed