Szwałek, Kacper, and Krzysztof Nadolny. “Characteristics of Tools Used in the Friction Drilling Method”. Journal of Mechanical and Energy Engineering 2, no. 2 (July 24, 2018): 109-114. Accessed March 20, 2019. http://jmee.tu.koszalin.pl/ojs/index.php/jmee/article/view/62.