With the rapid advancement of the machinery and electronics industries, CNC machine tools—particularly vertical machining centers—have become widely adopted in manufacturing. The structural design of these machines plays a crucial role in determining their rigidity, manufacturability, lifespan, and overall cost. Vertical machining centers typically use two types of counterweight systems: mechanical weights and hydraulic weights. While hydraulic weights offer a more compact design, they tend to be more expensive. As a result, most systems rely on mechanical weights. The support frame used for this purpose comes in two main structural designs. In this paper, we analyze both structures using finite element analysis software, such as ANSYS, to evaluate their strengths and weaknesses. This study holds significant value for the structural design of machining centers.
**1. Program Development**
The support frame is generally mounted on the top surface of the vertical column of the machining center. Holes are drilled at the front and rear of the frame to accommodate the shaft. A deep groove ball bearing, a shaft retaining ring, and a sprocket are installed on the shaft. One end of the chain connects to the headstock, while the other end is attached to the counterweight, allowing it to move back and forth between the front and rear sprockets. The schematic diagram and dimension drawing for Scheme 1 are shown in Figures 1 and 3, respectively, while those for Scheme 2 are presented in Figures 2 and 4.
**2. Part Analysis**
Structurally, the support frame of the first scheme weighs 41 kg, with a bottom contact area of 500 mm × 80 mm = 40,000 mm². It uses a single-side support method for the shaft end. In contrast, the second scheme’s support frame weighs only 19 kg, with a bottom contact area of 205 mm × 50 mm = 10,250 mm², and employs a bilateral support method for the shaft end.
From a technical standpoint, the first scheme has some advantages. It requires precise tolerances for two large holes (f40 mm), as well as for two smaller holes (f25 mm). However, from a mechanical perspective, the second scheme is superior. Under the same load—approximately 5,000 N each for the weight and the headstock—the second scheme supports the shaft at both ends. This configuration distributes the force more evenly across the support holes on either side, resulting in a lower bending moment compared to the first scheme. Therefore, the second design is more efficient and structurally sound.
For more detailed information, please download the attachment or refer to *Metalworking (Cold Processing)*, Issue 19, 2013.
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