Cutter Sharpening and Re-Grinding of Twist drill

The dimension precision and surface roughness of drilling, and drilling efficiency are directly related to the quality of cutter sharpening and re-grinding of twist drill.

In short, to avoid the cases as figure (b), (c), (d) during twist drill grinding that not only improve the drilling quality, but also will improve the drilling conditions, and come to prolong the service life of the twist drill.

Figure1: The impact of bit grinding on machining

(a) Grinding Correctly
(b) Point angle asymmetry
(c) Different Length of Cutter Grinding
(d) Point angle and Cutter Grinding are asymmetric

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The Check of Standard Twist Drill Bit after Grinding

Step 1: Checking the point angle (cutting lip angle) of standard twist drill bit is correct or not, and whether it is symmetric with the axis of the standard twist drill bit? (The correct point angle of standard twist drill bit is ±118°, if it be used to drill harder materials that the point angle can be extended to 120°;  if there are the softer materials, the point angle should smaller than before, but keep mind, do not smaller than 90°.)

Step 2: To check the length and height of two major cutting lip (major cutting edge) are consistent. Because the quality of the machined holes are affected by whether the length is the same.
The check method for step 1 and step 2 is that: Place the cutting part of twist drill bit keeps in a vertical position, keep eyesight at the horizontal level, and then repeatedly rotate 180°, where is the center axis of standard twist drill bit, to observe whether the length of two major cutting lips are same in rotation. It is an assumption that to observe the length of two major cutting lips at the center of axis; If the lengths of two major cutting lips are different, that the shorter side should be grinded.Continue reading

Cutting performances and Advantages of Ni Zhifu Ordinary Twist Drill Bit

Definition of Ni Zhifu Ordinary Twist Drill Bit: Based on standard twist drill that the cutting part is grinded onto a special shaped drill bit. The standard twist drill consist of two major cutting lips (major cutting edges) and a chisel edge. The most fatal weakness is that the negative front angle of chisel edge and dead center are larger, led to the cutting conditions are unfavorable. Ni Zhifu Ordinary Twist Drill Bit is that grinding two symmetrical crescent grooves based on standard twist drill, forming arc blade, and then sharpening two inner straight edges on the chisel edge and dead center. After that, with the chisel edge and original two straight edges, making the standard twist drill into “Three knife-points and seven knife-edges” that is the Ni Zhifu Ordinary Twist Drill Bit.Continue reading

How to ream or countersink holes by twist drill bits?

In actual work, we will encounter some special machining phenomenon, such as machining a larger diameter hole, or bottom of hole should beflat. Today, here we introduce reaming and countersinking, let’s go.

Countersink Holes usually involves countersinking flat-bottomed hole and countersinking tapered counter bore.

Countersink Holes usually involves countersinking flat-bottomed hole and countersinking tapered counter bore.

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How does the twist drill bit sharpen can be more sharper?

The twist drill bit is the most commonly used cutting tool, the twist drill bit wants to be sharpened, so pay attention to some points below to:

For mechanical processing, twist drill bit is the most important of drilling tool, in all itsstructure simplicity,but it’s not easy to sharpen it right. The keypoint is to master the sharpening methodsand skills.If the method is mastered, the problem will be solved.Let me introduce the manual grinding of twist drill bit.

Usually, the point angle of twist drill bit is about 118°,it could also be treated 120°, the sharpening skills as follows:Continue reading