OVERVIEW

In point-to-point machining operations, those consisting of drilling, reaming, tapping, boring, etc., we are often required to machine either a single hole or a series of holes with the same tool, usually followed by other tools. In practice, several holes are much more common than a single hole. Machining several holes with the same tool means machining a pattern of holes or a hole pattern. An English dictionary defines the word 'pattern' as a 'characteristic or consistent arrangement or design'. Translated to hole machining terms, any two or more holes machined with the same tool establish a pattern. The desired hole pattern is laid out in the part drawing either randomly (characteristic arrangement or design) or in a certain order ( consistent arrangement or design). Dimensioning of a hole pattern follows standard dimensioning practices.

This chapter describes some typical hole patterns laid out on a flat part and the various methods of their programming. To make matters simple, all programming examples related to hole patterns will assume a center drilling operation, using a #2 center drill, with chamfer diameter 0.150, to the depth of 0.163 (programmed as Z-0.163 - see page 202). Program zero (program reference point Z0) is the top face of part and the tool is assumed to be already in the spindle. For the purposes of clarity, no hole diameters or material size and thickness are specified in the examples.

From the dictionary definition above, we have to establish what makes...