Recently introduced by Sandvik Coromant (www.sandvik.coromant.com) is a new tool that allows machine shops to produce chamfered holes in a single operation, thus reducing the cost per hole while at the same time achieving extended tool life. Designed for ISO P (steel) and ISO K (cast iron) materials, CoroDrill 870 is an exchangeable tip range that now offers an insert-based 45deg chamfer drill as part of the Tailor Made D275 family of tools.

Tests on an automotive wheel hub machined from P1 low-alloy steel (190HB) have demonstrated the potential gains on offer. The new tool, used on a vertical machining centre with emulsion coolant, was used to produce 12.6mm-diameter holes with a 45deg chamfer through a 14mm-thick workpiece. Up against a comparable competitor product, the CoroDrill 870 chamfer drill achieved a total drilled length of 60m before tolerance limits were exceeded (compared to 30m for the competitor tool).

The CoroDrill 870 chamfer drill provides the option of one or two chamfer inserts, depending on requirements. The use of two chamfer inserts produces thinner chips; as a result, it is recommended for medium- or high-feed applications in unstable conditions — or where a large chamfer width is needed. Conversely, a single-chamfer insert produces a thicker chip and gives better chip breakage in stable, low-feed or small-chamfer-width applications.

A range of insert sizes is available. It is recommended that the same feed rate is used for drilling and chamfering. This is particularly important when drilling a blind hole, because a reduction in feed can result in (undesirable) long chips from the drilling operation.