Sumitomo Super Multi-drill XHT demonstrates lack of wander with hole-to-hole breakthrough on deep holes

Inca was commissioned to produce a series of key positional holes 3 mm diameter through 177 mm thick plate. These holes would enable its customer to perform wire EDM profiling of a very complex serious of forms and cut-outs around the part's periphery. Due to the almost 30:1 depth-to-diameter ratio of the 3 mm holes, Inca was very concerned over possible errors caused by drill wander and especially any drill breakage in the hole, so it called in its primary tool supplier Sumitomo Electric Hardmetal. A trial of the tooling company's latest Super Multi-drill XHT was set up and when the application was discussed in detail, it was decided to drill each hole to a set depth and then turn the component over, reposition against the datum and then drill to break through in the centre. To carry out the initial order for a batch of six, first 800 by 400 mm blanks made from EN 100 involved the plough ground plates being loaded on to Inca's Mazak VTC-300C-II travelling column vertical machining centre where two datum edges were milled for process location and the 3 mm dia holes drilled. The components were then shipped to the customer for EDM operations to be performed before coming back to Inca for a series of milled cut-outs and drilled and tapped holes to be produced around the outer profile. Sumitomo Electric Hardmetal's Super Multi-drill XHT incorporates its HT cutting geometry that introduces a 'double margin' on the leading edge and heel of the tool land. This adds stability to the tool when applied in deep hole drilling cycles and lowers the level of thrust required from the machine drive system. The geometry also helps to reduce the size of chips produced which are evacuated through the special fluting on the tool. In the Inca trials the lack of drill wander helped the precise targeting to achieve hole-to-hole breakthrough some 90 mm inside the part. A Sumitomo MDW-PHT pilot hole drill was used to ensure the start position and create a 'bushing' to stabilise the initial penetration and acceleration of the tool, the Multi-drill was run at 8,500 rpm and at a feedrate of 0.06 mm/rev. Tony Clifford Inca's works manager comments: "As we only had six blocks to produce with six holes on each side, initially it was lead time that was of the essence. We drilled to depth on one side, relocated the part and just before we reached the breakthrough of the two drilled holes from the second side, we took the precaution of going into hand feed on the Mazak. This was to ensure there was no snagging that might cause the tool to break as it was such a small diameter. "When we checked the breakthrough we were very surprised how straight each hole had been produced and even after a combined drilling depth of some 6,500 mm covering the complete batch, we found any wear on the tool was minimal." Mr Clifford often has rush jobs due to breakdowns at customers' plants, but he maintains that service and support to obtain the right tooling not floor-to-floor times are often the most important factor. He says: "What we need and are getting from Sumitomo is first class quality and cutting ability and very predictable tool performance." Following the machining of the blocks for the LHC the Super Multi-drill XHT was returned to Sumitomo at Princes Risborough for regrinding and recoating to bring it back to 'as new' condition ready for the next batch of parts. First published online