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1. First of all, you need to remember that the service life of drill bits increases with proper use, what material you are drilling into, what machine you are using, in compliance with cutting conditions, and whether you are using cutting oils or pastes. We will discuss this in other articles.
2. Like everything, sharpening a drill bit can be simple for some and complicated for others. In this article, we will deal with sharpening a metal drill bit.
3. Sharpening can be done on a hand-held disc grinder, which is a job for experienced grinders, using a jig or a special drill grinder. In an emergency or from a home workshop perspective, sharpening can also be done on an angle grinder. The best solution is to send blunt drill bits to our manufacturing plant, where we will resharpen them for you on professional machines by experienced staff. Contact a sales representative, visit our stores, or write us.
4. We recommend that you follow and copy the original geometry when resharpening the drill.
5. Metal drills have several basic types of main cutting edge, or relief in the center of the drill, where the cutting speed is zero and at this point the drill becomes a forming tool, not a cutting tool. The basic type is relieved cone, usually at an angle of 118° without relief. The next is the split point C, usually at an angle of 130°. The best is our unique patented geometry with a change and constant core thickness in the front part, CZ002 with a point angle of 118° and CZ004 with a point angle of 118°.
6. Most drills have a geometry that does not allow the same resharpening of the drill as you purchased it, due to the drill core, which expands from the tip to the shank, due to the rigidity of the drill. With each repeated resharpening of the drill, the core increases and with it the geometry of the drill changes. There are drills that have a constant core in the first part (with a core length of 3-5D), these are primarily unique drills CZ002 and CZ004 from the workshop of the NÁSTROJE CZ factory, where we assumed that you would want to resharpen the drills repeatedly. The geometry of the CZ002 and CZ004 drills is designed to be easy to resharpen, it is easier than with other types of drills.
7. When grinding the drill, the cross cutting edge becomes thinner. Then it is necessary to grind the lip angle, which varies depending on the material on which you want to sharpen the drill. Lip angle for hard material is usually in the range of 6-9°, for medium hardness 9-12° and for soft material 12-18°. When sharpening the drill, do not forget to check whether the length of the main cutting edge is symmetrical. Nose angle is no less important, where for drills for hard materials, such as stainless steel, nose angle is 130°, while for softer materials it is 118°.
8. The biggest problem arises in the relief of the center of the drill, where the cutting speed is low to zero and, as we have already mentioned, the material is pushed out in the center of the drill, i.e. forming. The stronger - thicker the core at the tip of the drill, the more necessary it is to relieve the drill with one of the relieves that we know. The most commonly used are split point C and A. The problem is the accuracy of split point, which will affect the quality of the drilled holes and the life of the drill. Grinding this relieve by hand is a job for truly experienced grinders. For this activity, we recommend BV13 or BV26 re-sharpening machines which are intended primarily for small and medium-sized operations.
9. Remember that if the drill has a damaged bevel, it will never drill properly again, even if the main cutting edge is resharpened.
10. Similarly, a damaged drill shank, for example by spinning in the chuck, affects the function of the tool and it is not good to use such a tool. For manual drilling, we recommend a shank equipped with three flats that prevent spinning in the chuck.
Other articles:
Testy vrtáků s novou geometrií
Vrták CZ005 - Nový člen rodiny
