1) Diameter set in the boring bar was not to the requirement.|2) Operator adjusted the boring bar and did not ensured the diameter after adjusting.|3) the boring bar was set to the required dimension when issued to the operator from the tool grip but before loading to the machine the operator re-adjusted the boring bare and did not ensured the diameter before loading to the machine.|4)Due to lack of confidence of the operator on the zoller machine the operator re-adjusted the boring bar thinking to achieve the bore in the minimal side and then we can correct the dimension but after re-adjusting the operator did not ensured to what diameter he has adjusted before loading to machine.