# Development and Field Testing of a Suspended Mulberry Branch Harvesting and Stubble Cutting Machine
## 3 Key Component Design
### Cutter Design
#### 3.1.2 Design of the Circular Saw-Type Cutter  
A customized circular saw cutter with material-feeding teeth was designed specifically for cross-cutting hardwood, as shown in Figure 4a. The cutter features a 400 mm outer diameter, 96 teeth, and a \(-5^{\circ}\) rake angle to enhance cutting power and wear resistance, ensuring smooth and precise cutting. The blade thickness is 4 mm, with a 30 mm central bore. Six evenly distributed \(\Phi\)5 mm mounting holes on a 166 mm-diameter circle provide stable and efficient cutting operation.  
As shown in Figure 4b, the circular saw blade is generally subject to the influences of axial force, tangential force and radial force. Among them, \(\omega\) represents the cutting rotational speed, \(V_{\mathrm{f}}\) denotes the feed speed, \(\alpha\) is the cutting inclination angle of the circular saw blade, and \(V\) represents the cutting linear velocity of the circular saw teeth. The cutting force F can be decomposed into radial force \(F_{\mathrm{i}}\), tangential force \(F_{\mathrm{f}}\) and axial force \(F_{\mathrm{a}}\). The radial force \(F_{\mathrm{i}}\) is mainly generated due to the impact of branches on the circular saw blade  
Figure 4: Schematic diagram of the circular saw. (**a**) 3D diagram of the circular. (**b**) Diagram of cutting forces on saw blades.  
during cutting and the reaction force caused by the bending deformation of branches on the circular saw blade. The tangential force \(F_{t}\) is mainly produced by the reaction force of the friction when the circular saw blade cuts branches. This force is parallel to \(V\) but in the opposite direction, as it is opposite to the direction of the cutting rotational speed. The axial force \(F_{a}\) is mainly caused by the machining errors and installation errors of the circular saw blade, as well as the extrusion and collision of oblique branches on the circular saw blade, and its corresponding direction is along the installation axis of the circular saw blade and perpendicular to the surface of the circular saw blade. To simplify the calculation, the resultant force \(F_{xy}\) of the radial force \(F_{n}\) and the tangential force \(F_{t}\) can be equivalently decomposed into a horizontal force \(F_{x}\) in the feed direction in the XY plane and a force \(F_{y}\) perpendicular to \(F_{x}\) in the XY plane for measurement and analysis. The axial force \(F_{a}\) can be equivalent to a vertical downward force \(F_{z}\) and a horizontal force \(F_{x1}\). The resulting cutting force \(F\) can be expressed by Equation (1):  
\[F=\sqrt{\left(F_{a}\times\cos\alpha+F_{a}\times\sin\alpha\right)^{2}+F_{n}^{2}+ F_{t}^{2}} \tag{1}\]  
In the saw cutting device, as shown in Figure 5, two circular saw blades are symmetrically mounted at the front end with a 390 mm spacing between the rotating shafts, and a 5 mm gap between the saw blades to optimize cutting. The top of the spindle integrates a 6\(-\)15 \(\times\) 20 \(\times\) 3 splined shaft sleeve, which fits seamlessly with the Yongbo 150 reversing splined shaft, ensuring transmission accuracy and stability. The spindle is supported by a 32,006 type tapered roller bearing, with a 20 mm circular ring spacer between the bearings, effectively dispersing axial loads and preventing blade movement. Special washers are added above and below the saw blades to expand the contact area, reduce vibration, and minimize the risk of vertical vibrations and collision damage. The bolts beneath the spindle use left-hand threads to reduce the risk of loosening and enhance operational safety.