Page 235 - Demo

233DEEP HOLE DRILLINGBTA Drill StructureDue to the large depth of holes to be drilled, the deep hole drilling tool is long. For ease of manufacture and operation, it is usually assembled in length. The BTA drill consists of a drilling head, which is assembled to the drill pipe (stem) using a rectangular thread with a coarse pitch - for fast and reliable fastening.The thread on the drill head can be internal and external, one or four-start, depending on the type of drill and the diameter of the drilling (Figure 6.6.2.1). The diameter of the drill pipe (stem) is smaller than the diameter of the drill head, which provides an annular gap between the walls of the machined hole and the outer diameter of the drill pipe.The stem of the tool, covering the length from the head to the end of the tool and serving to give the tool the required length, is the least rigid link in the deep hole drilling system. The profile and dimensions of its cross-section are chosen to ensure the highest possible rigidity while simultaneously performing the functions of supplying coolant to the cutting zone and removing chips by the coolant flow. The stems of the BTA system can be whole or composite in length.Figure 6.6.2.1Deep Single Tube Drills with External 4-Start Thread ConnectiondgapDDeep Single Tube Drills with Internal Single-Start Thread ConnectionD dgap