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In recent years, internal inclined wheel mechanisms have become increasingly popular in both civil and industrial applications. These mechanisms are commonly found in high-end residential electric curtains, automatic curtain lifting systems in theaters, automated door devices in home cabinets, and various small to medium-sized instruments, including those produced by our company, such as three-coordinate measuring instruments and tool presetting measuring devices.
After reviewing domestic and international information, it became clear that specialized internal inclined wheel mechanisms for precision instruments are primarily imported, which is costly and involves long lead times. When we contacted local bearing manufacturers, they refused to supply due to the small batch size and technical challenges involved. To reduce production costs and accelerate new product development, our company decided to conduct research on custom bearings designed for arc-shaped holes.
This article provides a detailed overview of our company's approach to optimizing the shape and processing and inspecting the inner ring of these special arc bearings.
**1. Special Bearings for Arc Holes**
An arc hole special bearing refers to a non-cylindrical inner ring bearing. The inner hole has an arc-shaped profile as shown in the figure. When this arc comes into contact with a cylindrical shaft, axial thrust is generated as the angle between the bearing and the shaft changes, causing the inner ring to rotate and resulting in axial movement of the outer ring.
According to domestic and foreign data, the inner arc shape is typically formed using a shaped diamond roller. However, the diamond roller itself is expensive, and the associated equipment adds significantly to the cost, especially for small-batch production. Using a diamond walking method also requires a custom grinding wheel mechanism, which is difficult to implement quickly.
Through analysis of the bearing’s working conditions, we identified that the arc section in the middle of the bearing is critical. Therefore, we negotiated with the Harbin Group to modify the design of the 100 inner rings they provided, changing the shape from Figure 1 to Figure 2. This simplifies the grinding wheel shape, making it easier to process. The Harbin Group used CNC lathes with annealing and turning processes to create the desired shape, then delivered the inner rings to the bearing manufacturer according to P6 precision standards. Finally, our company completed the finishing process.
**2. Finishing and Testing Methods**
To improve the accuracy of the arc hole, we designed and manufactured a custom fixture and clamp as shown in Figure 3. The fixture was designed based on the spindle center height of our existing grinding machine and the specific shape of the guide rail.
The setup involved placing screw 4 on the machine tool’s guide rail, securing positioning block 12 in the dovetail groove, and fixing member 4 to the guide rail using screws on member 10. Member 1 was fixed to piece 13 with two screws, and piece 3 was secured to member 1 using two screws. After adjusting the coaxiality of the fixture with the machine axis, screws 2 and 4 were tightened. A specially designed clamp 6 was used to bond the inner ring of the assembled 7-hole special bearing with a special adhesive, followed by mounting member 5 on clamp 6 for driving action. Three pieces were then placed into the large hole of piece 3. Finally, member 4 pressed the outer ring of piece 3, and the workpiece was secured with two screws 9.
Once the inner hole was shaped as shown in Figure 2, the intermediate portion could be ground into the desired arc by forming an R arc on the outer circumference of the inner grinding wheel. Piece 11, an elevated plate, was designed to match the existing wheel dresser. The wheel dresser was fixed on piece 13 through two through holes in piece 11, ensuring the diamond’s center aligned with the workpiece’s center, allowing for easy dressing during processing.
During the arc hole grinding process, the machine tool’s spindle was moved to the inner ring of the clamp to meet the grinding requirements. Due to the self-grinding method used, the inner arc of the special bearing achieved a relatively high rotation precision (most arcs measured at 0.006 mm). To ensure symmetry within 0.1 mm, a universal tool microscope was used. The arc hole bearing was placed in a V-groove, one side was aligned with the baffle, and a lever-type inductor comparator was inserted into the hole to contact the arc. The microscope slide was moved to the highest point of the arc, and the reading X1 was recorded. The bearing was then rotated 180°, and the same process was repeated to record X2. The symmetry error was calculated as (X1 - X2)/2, and the machine table was adjusted accordingly. Through these steps, we successfully produced a batch of special arc-hole bearings that met the required specifications, addressing an urgent production need.
**3. Conclusion**
The inner arc hole rounding of the special arc hole bearing has reached the precision level of well-known foreign brands. Additionally, the overall assembly performance has slightly exceeded that of foreign counterparts. These results have been successfully applied to our new products, including the 4618 tool inspection instrument and the 1640 knife adjustment instrument.