What to do if the drill does not drill at all. A positive rising clearance angle is the main condition for good drill performance.
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• ЗАТОЧКА СВЕРЛА. Самое...
Shows how I sharpen a drill in practice.
With emphasis on the fingers, I position the drill so that the cutting edge is parallel to the axis of rotation of the abrasive wheel.
At the same time, the existing sharpening of the drill is maintained, that is, the angle at the top (the angle between two cutting edges) is maintained, which is approximately 120 °.
And what is especially important:
The axis of the drill must be, firstly, above the axis of the abrasive wheel.
And secondly, the shank must be omitted. And in the process of sharpening, it fell even more.
Both are necessary to obtain a positive increasing relief angle - the main condition for good drill performance.
After the cutting edge is sharpened, the drill is not retracted, but the rear surface is further sharpened. In order to increase the clearance angle, the shank is further lowered.
Smooth movements are made.
After one cutting edge is sharpened, without changing the position of the hands, the drill is rotated 180 ° around its axis and the other cutting edge is sharpened.
The position of the hands does not need to be changed in order for the angle at the top to be symmetrical.
Drill sharpening shown.
It is shown with examples what is important for the operation of the drill: a sufficient clearance angle and a lowering of the rear plane, that is, an increase in the clearance angle as it moves away from the cutting edge.
It can be seen from these examples that if the clearance angle is very small, or even not small, but does not increase with distance from the cutting edge (there is no lowering of the rear plane), then the drill does not cut, does not work at all.
Shows how a properly sharpened drill drills.
According to established recommendations, when sharpening a drill, 4 parameters must be observed:
First, it is necessary to provide a positive clearance cutting angle.
Secondly, the angle at the top should be approximately 120° depending on the material, it is slightly different.
Thirdly, the angles between both cutting edges and the drill axis must be the same, that is, the angle at the top with respect to the drill axis must be symmetrical.
Fourth, the length of both cutting edges must be the same.
For the operation of the drill, the most important is the first condition - a positive relief angle. If it is not performed, then the drill does not drill at all. Which is what I showed in this video.
Other parameters affect the accuracy of drilling. The drill will not cut, no matter how accurately the other conditions are met, unless a positive relief angle is provided.
In one of the previous videos, I showed and proved that the value of the angle at the top (about 120 °) does not significantly affect the operation of the drill:
• ЗАТОЧКА СВЕРЛА. Угол п...
In one of my videos, I already showed that even with an inequality in the lengths of the cutting edges, the drill works well:
• ЗАТАЧИВАНИЕ СВЕРЛА
This video shows with examples that the drill will work with different angles at the top, and with different lengths of the cutting edges.
I sharpened the drill specially with different angles at the top of the cutting edges. Although the 115° apex angle is normal, it is not symmetrical. The drill works, and works quite well, even with one cutting edge.
Then he sharpened the drill specially with different lengths of cutting edges - 4.9 mm and 5.9 mm. The drill works and works well.
You just need to keep in mind that in both cases the hole breaks a little. But this is often not important, and sometimes it can even come in handy.
The sharpening of the jumper is also of secondary importance.
It is shown on an example that even with a very wide jumper, the drill will still drill.
Once again, I emphasize that the main thing when sharpening a drill is to ensure the necessary back angle.
And the value of the angle at the top, the equality of the angles between the cutting edges and the axis of the drill, the equality of the lengths of the cutting edges, the length of the jumper - all this is not of decisive importance for drilling.