Angle of sharpening of a drill on metal: table and recommendations
Drills on metal, like any other cutting tool, wear out during operation, which makes them unusable. Meanwhile, in most cases, the cutting and other angles of the drill on the metal can be restored, selecting their values according to a special table and sharpening.
Manual sharpening of a drill on metal
Purpose and design features of the tool
Drills on metal, for the manufacture of which steel alloys of high-speed group are used, are used for creation in metal details as through, and blind holes. The most common are twist drills, the design of which includes the following elements:
- cutting part;
- working body;
- shank;
- lapku.
Structural elements of a spiral drill
If the shank, which can be both cylindrical, and conical, is intended for reliable fixing of the tool in the cartridge of the used equipment, the working part simultaneously performs several important functions. It is the geometry of the drill that determines its performance and cutting properties.
The most important elements of the working part of the drill on the metal are screw grooves. Their task is, to remove chips from the processing area. The geometry of the twist drill on the metal provides, that the front side of the spiral groove is made at a certain angle, the magnitude of which in the direction from the axis of the tool to its peripheral part varies. In the process of making a drill for metal on the side of its spiral elements, narrow strips are formed, slightly protruding above the main surface. The task of such tapes is, to reduce the amount of friction of the tool against the walls of the molded hole.
Features of different types of sharpening drills
Sharpening of drills, as mentioned above, necessary for that, to restore their geometric parameters. The choice of a particular type of sharpening drill depends on a number of factors (tool diameter, characteristics of the processed metal, etc.).
Normal sharpening is the most universal (N), when performing which on the working part of the drill are formed one transverse and two cutting edges. The sharpening angle of the drill in this case is 118-120 °. Choosing this type of sharpening drills, should be borne in mind, that it can be used in relation to tools, whose diameter does not exceed 12 mm.
Types of sharpening drills on metal
All other types of sharpening, which are denoted by the letter combinations of NP, NPL, DP, DPL, can be used for tools with a diameter of up to 80 mm Each of these types of sharpening involves bringing the geometry of the drill on the metal to the required parameters.
NP
This sharpening involves undercutting the transverse edge, which is done to reduce its length and, in accordance, to reduce loads, perceived by the tool in the drilling process.
NPL
In this case, in addition to the transverse edge of the sub-point and the tape, which allows to reduce its width in the area of the cutting part. Sub-point of the tape in addition to reducing the friction force, created by drilling, allows you to form an additional rear corner of the drill, which facilitates the processing process.
DP
This is a double sharpening, combined with the subpoint of the transverse edge. Execution of sharpening of this kind allows to form on a working part of a drill on metal one cross and four cutting edges, having the form of broken lines.
DPL
This is similar to the previous type of sharpening, in which the tape is additionally undermined. Creating four cutting edges when performing double sharpening is necessary for this, to reduce the angle between the peripheral sections of the cutting edges. This approach improves heat dissipation from the cutting part of the tool and, in accordance, significantly increase its stability.
How to choose the right sharpening angles
Drill sharpening angles, as mentioned above, determined by special tables, where their values are presented depending on, in what material it is necessary to form an opening.
Table 1. Angles of sharpening of a drill on metal for various materials
If you choose the wrong angles, under which the drill will be sharpened, then it will lead to that, that it will become very hot during operation. This can eventually lead to its breakdown. in addition, the wrong angles are selected, used for sharpening drills on metal, often become the main cause of poor drilling.
Execution of the operation
Traditionally, sharpening drills on spiral metal is performed on an emery board, equipped with a grinding wheel of appropriate hardness. It is necessary to begin to sharpen them from processing of a back surface. Pressing the tool with this surface to the rotating grinding wheel at a certain angle, you need to watch out for that, that on it the correct bias was formed.
When sharpening the front cutting surface, it is necessary to control not only the angle, under which the operation is performed, but also the size of the jumper. Very important, that at sharpening on a working part of a drill on metal cutting edges of equal length were formed, located at one angle. If you drill a hole with a drill, when sharpening which these important requirements are not observed, then the diameter of such a hole will be larger, than the transverse size of the tool itself.
Check sharpening angles with a template
Check the compliance of the basic geometric parameters (including sharpening angle) drills of the necessary characteristics are possible by means of one template, which is easy to buy in series or make your own.
And finally a little video about it, how to sharpen a drill on metal.
