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This article presents a new practical approach to gain a better insight into the machinability enhancements of ultrasonic-assisted drilling (UAD) of aluminum alloys where the depth ratio is larger than 10. UAD can provide a depth as up to two times compared to that of conventional drilling (CD). The material removal rate of UAD appeared higher than that of CD by 1.5 times. The total drilling torque was considered to consist of three components: the cutting torque, the rubbing torque and the stick-slip torque. Both rubbing torque and stick-slip torque magnitude in CD were higher several times compared to the cutting torque. In contrast, such components in UAD took a small proportion of the cutting torque. Growing rate of the rubbing torque at deeper holes in UAD was slower than that in CD about 33 times. The effect of ultrasonic assistance on the reduction of chip resistance was found to be more effective at high depth ratio. The new approach gives better insight to understand the effects of ultrasonic assistance in deep drilling and would further develop to apply in similar studies. [ABSTRACT FROM AUTHOR]