The general shaft parts consider the outer circular grinding process and attach the design center hole on the part drawing as the positioning reference. There are two common standards for center holes.
Type A center hole for 60° cone is the working part of the center hole, supported by the top 60° cone, plays the role of the center, while bearing the grinding force and the gravity of the work-piece. Small cylindrical holes on the front end of the 60° cone store lubricants to reduce friction between the center hole and the center hole during grinding. B type center hole, with 120° protection cone, it can protect the edge of 60° cone from bruise. common in high precision and long process work-piece. When one end of the shaft can not drill a center hole, a cone Angle of 60° can be used instead, or artificial positioning base can be used. Such as the center hole plug, to meet the requirements of the center hole processing technology. The center hole plug of the sleeve part is provided with a small hole to meet the flow of cutting fluid and play a cooling role. Center hole plug with special structure for large precision rotor parts. The material hardness of the rotor is low, so the center hole made of hardened steel can bear great pressure to achieve high machining accuracy.
Technical requirements for the center hole:
(1)The roundness tolerance of 60° taper is 0.001 mm.
(2) 60° conical surface shall be inspected by gauge colouring method, and the contact surface shall be greater than 85%.
(3)The coaxiality tolerance of the center holes at both ends is 0.01 mm.
(4)The surface roughness of 60° conical surface shall be RA0.4 um or smaller, and there shall be no burr, collision and other defects
In order to meet the requirements of the center hole, the following methods can be used to repair and grind the center hole:
1.Grind the center hole with a whetstone and rubber grinding wheel. First, the cylindrical grindstone or rubber grinding wheel is installed on the lathe chuck, and the diamond pen installed on the tool holder is used to repair its front end into a 60° sharp Angle. A small amount of lubricating oil must be added to reduce the surface roughness value of the center hole, so that the quality of repairing and grinding is higher.
2.Grind center holes with cast iron tips. The abrasive formulation is white corundum (F500) 16g, stearic acid 8g, beeswax 1g, aviation gasoline 80g, kerosene 80g.
3.Grind the center hole with the forming inner wheel. The grinding wheel is trimmed into a sharp Angle of 60°, which is suitable for repairing the center hole with deformation and large size.
4.Squeeze the center hole with a four-edged carbide tip. Extrusion carbide top with four conical edge belt, extrusion is generally in the vertical center hole grinding machine, suitable for mass production.
5.Grind center hole with center hole grinder. The grinding wheel makes planetary grinding motion and makes feed motion along 30° Angle direction. Center hole grinder is suitable for grinding hardened precision parts with center hole roundness up to 0.0008 mm.
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