Not every drill takes hardened and hard steel. In this regard, if it is necessary to drill a bearing race, knife blade or other hardened products, difficulties arise. To solve them, you can make a homemade drill that can cope with complex tasks.
Materials:
- ball from under the bearing;
- self-tapping screw
Making a drill
You need to select a ball that matches the diameter of the required hole. It can be taken from a new or old used bearing. To quickly remove the bearing, it is better to wrap it in cloth and break it with a hammer. The rag will prevent the balls from flying around the workshop.
A regular black wood screw will be used as the base of the drill. The main thing is that its length is enough for the required drilling depth. The screw head is ground down so that its diameter becomes slightly smaller than the ball.
A small nut is clamped in a vice and the ball is placed on it. The nut is used as a temporary stand, so the quality of its thread and the condition of the edges do not matter.
The head of the screw is attached to the ball and they are welded together.
The weld protruding beyond the diameter of the ball must be sanded off. In this case, it is important to turn the self-tapping screw in order to obtain a cylinder without corners.
The ball is then ground for a twist drill. If you need to drill a tile, then it is given the shape of a feather.
Having received the desired shape, the drill is hardened. After welding and grooving, the ball loses its hardness, so it needs to be restored. To do this, the tip of the drill is heated with a gas burner until it turns orange and is immersed in oil for a few seconds. At the same time, the screw itself and the welding do not need to be cooled so that they do not become brittle.
After hardening, the drill tip is finally sharpened. This should not be done on tempered metal before hardening, since then the quality of the cutting edge will be worse.
The resulting drill drills well into almost any hard metal, be it a bearing race or a file. The main thing is not to overcool it. If you don’t have oil on hand, you need to add at least water into the hole.
When drilling very thick steel plates, so as not to suffer from constant cooling, you can put a rubber ring around the punched point and add water to it. The liquid will be held by surface tension and constantly cool the drill.
