Fig. 5
![Fig. 5](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs40759-017-0019-z/MediaObjects/40759_2017_19_Fig5_HTML.gif)
Microscopic images of hollow drill tool using a Dino lite microscope (a) new drill bit (b) after 30 drills (c) after 50 drills (d) after 100 drills
Microscopic images of hollow drill tool using a Dino lite microscope (a) new drill bit (b) after 30 drills (c) after 50 drills (d) after 100 drills