Also known as ring core drill holes drilled, which is a material saving, energy saving, efficient, high quality deep processing tools, productivity ten times higher than the drill. Thus, the hole diameter greater than 50mm, preferably trepanning drilling process.
Core drill is mainly used in the following situations:
　　(1) linear and positional accuracy of the hole has higher requirements than the aperture hole of 50mm.
　　(2) an aspect ratio of more economical use of core drill hole between 1-75
　　(3) The workpiece materials are expensive or core material testing and chemical analysis to be carried out, the need to retain the integrity of the core than expected.
　　(4) The machine power shortage, and require drilling large diameter holes.
　　Depending on the way the chip is divided into inner and outer chip chip; from the structure can be divided into single tooth and multiple tooth core drill core drill. BTA core drill, cooling fluid through the oil cooler grant clearance to flow after nesting drill hole section drill pipe outer wall of the workpiece, cooling the cutting edge, and then with the chips by chip rim drill core drill inner wall quilt out of the work spindle outer wall voids excluded. Typically, drain oil gap is half the width of the cut.
The main advantage of BTA core drill are:
　　(1) drill pipe cross-sectional area than the outer chip mode, therefore the good rigidity
　　(2) cooling liquid to lubricate and protect the guide block, the chip will not scratch the surface of the cell walls, get better dimensional accuracy and low surface roughness.
　　(3) Coolant can better suppress the vibration of the drill pipe.
　　(4) Since the nesting space drilling fluid flow exhaust port is reduced, so that the coolant flow speed, accelerating the flow of chips, enhanced chip removal.
　　Outside chip core drill, drill coolant is a gap with the inner wall of the workpiece spindle fitted between the outer wall of the flow of nesting drill unit, cooling the cutting edge, and then with the chips have workpiece drill hole wall and the outer wall gap discharge. Should normally be the oil discharge gap is only slightly larger than the area of ??the gap area, in order to facilitate chip evacuation. In order to successfully chip, chip needs to have enough space, it must reduce the respective outer diameter of the drill pipe, thus weakening the drill rigidity.
External chip set core drill advantage of:
　　(1) does not require a dedicated oil cooler grant, simplify processing system.
　　(2) the same aperture core drill drilling, drill nesting outside chip chip chip area larger than the inner core drill.
　　(3) outer core chip channel sectional shape of the handle material impact.
　　(4) The large diameter. Large aspect ratio of the nesting process, the use of outside chip approach is more reasonable. Because the cut-out mandrel too heavy drooping blade will generate pressure, causing chipping, it can be set after the guide block and the center is holding.