inside of the drill. It flows back outside the drill, through the flute, bringing the chips with it. BTA / STS (Boring and Trepanning Association / Single Tube System) - The cutting tool is a tube. Coolant is pumped in around the outside of the cutting tool and carries chips out through the center tube. For the tube to be strong enough and have an inner diameter large enough to carry chips away, the hole must be more than in diameter. Ejector system - The cutting tool is a tube with another tube nested inside. Coolant flows through the smaller tube to the cutting face and then coolant and chips flow back through the larger tube. This is only an acceptable technology for holes of over in diameter. References Further reading [Machinery editors]. (1910) Deep hole drilling, 2nd edition. Machinery's Reference Series Number 25. A small monograph on gun drilling practice as of 1910. Compiled as part of a series by the editors of the journal Machinery by revising and republishing information from the journal. Reprinted, along with 2 other Machinery articles on deep hole drilling from 1926 and 1927, by Lindsay Publications, Inc, . External links Lilja article on rifle barrel drilling Gun drill article on definition and applications of gundrilling Firearm construction Hole making