A circular adjustable drill, popularly known as a “ballerina,” is a device designed to drill round holes of the required diameter. Such a drill will be most welcome in situations when it is not possible to use a milling machine or a jigsaw when working with wood and materials based on it (chipboard, fiberboard, plywood, etc.) for certain reasons, be it the inconvenience of using them in a particular case (for example, when working with already assembled the furniture, uneven surface, etc.) or simply the absence of such a tool at hand. Note that this drill can also be used when working with drywall and plastic.
Design fixtures extremely simple - it consists of two movable carriages with cutters mounted on a transverse rod with markings engraved on it, which allows you to adjust the required distance between the cutters and the centering support element - a drill. The drill itself, as well as the blades, can be easily removed, which allows them to be replaced or sharpened (including at the required angle).
Note that the drilling range is limited by the size of a particular “ballerina”. The maximum drilling diameter depends on the length of the rod itself, and the minimum depends on the thickness of the shank. The recommended thickness of the material to obtain smooth edges at the cut ~ 20 mm. This seller has drills that allow you to drill circles of the following diameters:
• min 30mm - max. 120 mm;
• min 30mm - max. 200 mm;
• min 30mm - max. 300 mm;
Each comes with a hexagon and a tap.
In conclusion, it should be added that it is best to start drilling at low speeds in order to minimize the chance that one of the cutters will jump off. Also, for a more accurate cut, it is recommended to lightly sand their surface.
Cost: ~ 600