The umbrella rotary top, also known as the large-headed top or pipe top, is primarily used to support sleeve components. It can endure higher cutting loads, enhance the stiffness of workpiece support, and reduce deformation during machining. According to the "National Standard for Positioning, Clamping, and Device Integrated Labeling - JB/Z174-82," there is a mention of the "umbrella-shaped top with positioning and lever clamping" in the circular outline of the tube blank. Plum blossom-shaped tops are also commonly used in processing, particularly for positioning and clamping the umbrella-shaped top.
The cone angles of these umbrella-shaped or plum blossom-shaped tips are typically 60° or 75°, with some reaching 90°. The main advantage of the large cone angle umbrella-shaped rotary top is its versatility, as one tip can process workpieces with internal hole sizes ranging from tens of millimeters to over 100 mm. However, it has a drawback: low positioning accuracy and significant error in end face positioning. To address these issues, the author designed and manufactured a series of small cone angle rotary tops. After several years of practical testing in production, the results were very satisfactory. Below is an introduction to the small cone angle rotary top.
**1. Structure of the Small Cone Angle Rotary Top**
[Image description: A schematic diagram showing the structure of the small cone angle rotary top.]
1. Taper sleeve
2. Cap
3, 4. Washer
5. Screw cap
6. Taper shank
7, 13. Screw
8. Lever
9, 11, 12. Bearing
10. Oil cup
14. Screw plug
The figure above shows the structure of the small cone angle rotary top. The solid line represents the structure where the small end of the sleeve is smaller than Ø30mm, while the double dotted line indicates the structure where the small end is larger than Ø30mm. The standard cone angle is generally 30°, but for improved positioning accuracy, it can be reduced to 20° or even 15°. The cone material is 9Mn2V, heat-treated to 60–64HRC, ensuring high hardness and wear resistance, which extends its service life. The taper shank is made of 40Cr and heat-treated to 40–45HRC.
When a clearance seal is used between the taper shank and the screw cap, the clearance should not exceed 0.2 mm. For larger small taper rotary tops (d0 > Ø100 mm), a felt seal is preferred. Two single-precision radial ball bearings ensure high positioning accuracy and the ability to withstand radial forces. An E-class precision thrust ball bearing is used to handle axial loads. The tolerance zone for the bore of the bearing sleeve and the bearing is M7, while the shaft tolerance for the taper shank and the radial ball bearing is h6, and for the thrust bearing surface, it is j6.
During assembly, grease is filled into the rotating top’s bearing and the screw cap hole. After adjusting the bearing clearance, the screw cap is tightened using a screw. Finally, the Morse taper shank is inserted into the taper hole of a universal cylindrical grinding machine. The cone sleeve is then rotated by a dial to finely grind the cone surface, ensuring compliance with shape, position, size, and surface roughness requirements. This method is also effective for repairing worn or deformed cone surfaces.
**2. Application in Manufacturing**
This small cone angle rotary top is widely used in our factory for processing long bushings of tubular pumping products, which are 300 mm in length. These bushings have five different nominal inner diameters: 32, 38, 44, 56, and 70 mm, with wall thicknesses ranging from 5.5 to 8 mm. The outer circumference of the hardened long liner is ground using this method.
Two small cone angle rotary tops are installed in the taper holes of the cylindrical grinding machine spindle and tailstock (a lever must be added to the spindle). The friction force between the workpiece’s hole periphery and the taper sleeve drives the workpiece to rotate. The tailstock's compression mechanism forces the workpiece against the grinding wheel to finish the outer circle. The surface roughness reaches Ra 0.4 μm, roundness is within 0.005 mm, and the coaxiality between the outer diameter and the inner hole is less than 0.01 mm (excluding shape errors of the hole). Workpiece loading and unloading is fast and convenient. Compared to traditional methods like ball spindles or cylindrical mandrels, this technique significantly reduces labor intensity and improves efficiency several times, earning high praise from workers.