Such drill bits are used to drill holes in materials that ordinary drill can simply damage (glass, tile, some types of plastic, etc.). These crowns are made in the form of a steel tube equipped with a groove for removing chips or picking out the drilled part of the material, and with a cutting part coated with diamond spraying. The shank is hollow, cylindrical, its diameter is 7 mm. The process of working with such drills is fast enough, the edges of the resulting holes are quite smooth, no large chips. It is recommended to carry out the work at 1000-1500 rpm, wetting the crown with water so that it does not burn out. In order for the crown not to slide on the surface of the material, but to start cutting exactly where it is necessary, the crown should be placed at an angle of 50 or 60 degrees and gradually level it. It is also highly desirable to fix the treated surface (for lack of a vise, you can fix the surface with at least ordinary adhesive tape or electrical tape).
The package includes 15 drill bits of the following diameters: 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, 22 mm, 25 mm, 26 mm, 28 mm, 30 mm, 40 mm, 50 mm. They come in a regular zip-lock bag.
In general, these crowns adequately perform their tasks under simple operating rules. But nevertheless, for all its merits, these drills have a minus - they have a resource of several tens of holes, so they are most likely not suitable for everyday use, but from time to time they are quite suitable for themselves, and the price of such a set relatively not high. If large diameter crowns are required, they can be purchased one at a time. here
Cost: ~ 750