| 摘要 |
Drilling apparatus for trepanning a difficult to work material. A drill member includes a very thin wall cylindrical cutting head integral with a shank portion, with the assembly being machined from the same piece of stock to insure concentricity. A fluid supply collar includes lower and upper Teflon washer inserts which surround the shank portions and which are held in place respectively by a shoulder of the cutting head and a chuck or other holder of a machine which rotates the drill member. Fluid supplied to the collar is directed through radial and axial passageways in the drill member to the lower margin thereof, and which lower margin includes a continuous abrading surface on the inside, outside and edge thereof. The length of shank extending from the holder is extremely short due to the dimension of the collar thereby resulting in high stiffness to insure for concentricity during drilling operations. A power down feed arrangement is provided so that the drill member is advanced into the workpiece at a predetermined constant rate.
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