Hello.
A rule of thumb is not to spot for full carbide drills and use pilot drills instead (for 7xD and up). However, half of the tool magazine are drills so it's not possible to have a pilot drill for every one. There are 140 degrees pilot drills and for example Guhring has one. Does anyone use them? I have learnt by experience that as short as 7xD drills (we use Sandvik R840 and R860.1 mostly) make a "bzzz" sound upon entering the material and the hole is tapered about 1xD length. Sometimes less and sometimes more, depending on how dull the drill is. I was hoping that a spot drill would eliminate this problem.
A rule of thumb is not to spot for full carbide drills and use pilot drills instead (for 7xD and up). However, half of the tool magazine are drills so it's not possible to have a pilot drill for every one. There are 140 degrees pilot drills and for example Guhring has one. Does anyone use them? I have learnt by experience that as short as 7xD drills (we use Sandvik R840 and R860.1 mostly) make a "bzzz" sound upon entering the material and the hole is tapered about 1xD length. Sometimes less and sometimes more, depending on how dull the drill is. I was hoping that a spot drill would eliminate this problem.