The shank of a solid carbide milling cutter
The shank of a solid carbide milling cutter is mainly a straight shank with a complete cylinder (see Fig. 3-35) and a cylindrical shank with a cutting plane (commonly known as "side-mounted" or "side-mounted").
3-35
Straight shank
The shank of a straight shank cutter is a complete cylinder, so the shank itself has good accuracy and clamping centering. The so-called straight shank does not mean that the diameter of the shank and the diameter of the working part D. are the same basic size. Sometimes, the diameter of the working part D will be larger than the diameter of the shank (Dd), which is called "shrinking"; On the other hand, the diameter of the working part D. will be smaller than the diameter of the shank (D.<d,), which is called "diameter increase", as shown in Figure 3-36.
When clamping a straight shank with a general clamping method (such as a spring chuck), the main reliance is on friction, so sometimes the clamping force is insufficient. If a straight shank structure is used for a large helical angle milling cutter with a large axial force, it is easier to pull out the chuck, especially when the "gouge" phenomenon as shown in Figure 3-5a occurs.
Therefore, if you are using a large helix cutter for side milling/slot milling, you should use a safer chuck, such as a power chuck or a chuck with a Safe Lock, or you can use a cylindrical shank with a cutting plane as described below.
Another major shank structure of cylindrical shank solid carbide end mill with cutting plane is cylindrical shank with cutting plane (see Figure 3-37). The drive of the cutter with a cutting plane does not depend on friction, it depends on the forced driving force of the cutting plane, so there is no slippage. At the same time, the cutting plane also restricts the milling cutter in the axial direction, and the phenomenon of "tool drop" does not occur.
3-36
3-37
Cylindrical shank with a cutting plane.
Another major shank structure of solid carbide end mills is a cylindrical shank with a cutting plane (see Figure 3-37). The drive of the cutter with a cutting plane does not depend on friction, it depends on the forced driving force of the cutting plane, so there is no slippage. At the same time, the cutting plane also restricts the milling cutter in the axial direction, and the phenomenon of "tool drop" does not occur when the cutter is withdrawn.
Depending on the diameter of the shank, this structure can be either as shown in Figure 3-37 with only one cutting plane, or larger with two cutting planes. These two are not two standards, but only two types of standard shanks in different size segments. However, because the structure of the two cutting planes is used when the diameter of the shank is greater than or equal to 25mm, the milling cutter of 20mm and below is basically a single-cutting plane structure.
Due to the cutting plane, the center of gravity of the shank theoretically deviates slightly from the axis of the shank, and this is on the side of the pressure surface. This will be used in the following analysis.
Although this structure can avoid some problems of the straight shank driven by friction, there are also three disadvantages.
1) The first disadvantage is that the coaxiality of the tool and the tool holder is not good. There is theoretically always a little gap between the cylindrical shank with a cutting plane and the cylindrical hole for its clamping. When the cylindrical shank is loaded into the round hole of the tool holder and locked with a screw, the tool is pressed to one side, and its clamping state is shown in Figure 3-38, the axis of the tool and the axis of the tool holder will produce an offset, resulting in different axes of the tool and the tool holder.
2) The second disadvantage is poor contact rigidity. As can be seen from Figure 3-38, after the cutter is clamped, one side of the cutter has a narrow contact band with the shank, while the other side does not. The size of the contact zone and the size of the void are narrow and the gap is too large, which causes the contact surface to be easily deformed, and this deformation can adversely affect the tool holder interchangeability.
3) The third disadvantage is that the dynamic balance is not ideal. In addition to the imbalance caused by the flattening structure itself, such as the small eccentricity of the center of gravity of the tool holder and the axis of the tool holder, which is mentioned earlier, this imbalance is exacerbated by the compression process. This is very disadvantageous for high-speed machining.
3-38
