End milling of circular pockets to meet geometric tolerances

Machining with an uneven chip load can lead to dimensional errors on workpiece surfaces. Tool deflections are liable to occur especially when machining with slender end mills where tool flexibility is high compared with that of the machine structure. Whilst steady state machining errors are commonly considered, it is more difficult to deal with the transient errors that occur at tool entry and exit to cuts. Using a predictive equation that links tool deflection to chip load, it is possible to compare expected errors of form or position with standards set out using geometric dimensioning and tolerancing. Machining conditions can be investigated to establish whether part features can be manufactured within tolerances allowed. A process for selecting machining conditions for producing a circular pocket is introduced. The use of a tolerance analysis chart is demonstrated to clarify the results of machining at tool entry and exit.