The proper use of drill bits on CNC applications is important. Using 10mm shank drill bits (with flat set screw land on the shank) in a standard collet/tool holder setup can lead to vibration. This causes poor finish, oval holes and chipping. When compared to spiral router bits, drill bits are run at a slower RPM (typically 6000-9000 rpm at 2 – 5.5/m/min) and while breakage might be tolerated if only drilling the occasional hole, it can become expensive for larger production runs. The reasons for this problem are two-fold:
1) You’re using a 10mm shank bit (w/flat on shank): Most metric drill bits have a 10mm shank with a flat area machined onto the shank (for set screw tightening). When inserted into a 10mm collet the flat spot prevents the collet from concentrically gripping the shank all around. (see red arrow in image above).
The solution: Our small 6381 drill adapter that goes between the collet and the drill bit fills this space and allows the collet to concentrically grip the shank. This adapter has a 10mm cylindrical shank (no flat) to go, which accepts the 10mm shank w/flat drill bit, tightened with a set screw as is standard on boring machines.
2) Using cylindrical shank bits (no flat on shank): Many in-between or uncommon sizes of cylindrical shank drill bits don’t fit snugly into the closest collet size available and therefore slip or chatter during the drilling process.
Another alternative solution: a Universal drill adapter (6380) which comes in two diameter ranges, infinitely adjustable within the specified range. (accepts 1-13mm diameter drills, or 3-16mm diameter) and is available in HSK63 F, ISO/SK30 and SK40 version. The 6380 Universal Drill Adapter has high-clamping power and accuracy and can be run either clockwise or counter-clockwise. For more information, please call us at 800-544-8436 or email firstname.lastname@example.org
Recommended rpm and feed (progression) of drill bits:
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