When the depth of the hole is many times of the diameter of the hole, the deep hole drilling method is needed. For more than 70 years, single edge deep hole drill (gun drill) is a common tool for machining deep hole with diameter less than 40mm. But in practical application, the processing efficiency of single edge deep hole drill is low, which leads to the rapid development of solid carbide deep hole twist drill. The development of solid carbide deep hole twist drill is the result of the improvement of tool manufacturing accuracy and groove and guide edge design. However, this kind of deep hole twist drill can only process holes with relatively small depth / diameter ratio. For deeper holes, single edge deep hole drill should be used. Compared with the solid carbide single edge deep hole drill, the two edge symmetrical twist drill can adopt much higher feed speed, so there are many such tools on the market, but its disadvantage is that the quality of the hole is poor, and it can only be used in the occasions where the processing requirements are not high.
On the contrary, through the comparative test, we can see that the advantage of single edge deep hole drill is that the drilling quality is higher, but the disadvantage is that the feed speed is smaller. When machining quenched and tempered steel, if the feed rate is increased, the tool wear will increase and the chip shape will be bad. Therefore, low machining efficiency and short tool life are the disadvantages of ordinary single edge deep hole drill.
