In processing and production, there are three kinds of keyways on the shaft: through groove, half through groove and closed groove. The through groove on the shaft and one end of the groove bottom are arc-shaped half through grooves, which are generally milled with a disk-shaped groove milling cutter. The width of the shaft groove is guaranteed by the width of the milling cutter, and the arc radius of the groove bottom at one end of the half through groove is guaranteed by the radius of the milling cutter. The closed groove on the shaft and the half through groove with right angle at one end of the groove bottom are milled with a keyway milling cutter, and the diameter of the keyway milling cutter is determined according to the width of the shaft groove.
1. Clamping and correction of workpiece
When clamping the workpiece, it is not only necessary to ensure the stability and reliability of the workpiece, but also to ensure that the axis position of the workpiece remains unchanged, so as to ensure that the central plane of the shaft groove passes through the axis. Common clamping methods are as follows:
(1) Clamping with flat tongs: clamping the workpiece with flat tongs is simple and stable, but when the diameter of the workpiece changes, the axis of the workpiece will change in the left and right (horizontal position) and up and down directions, affecting the depth dimension and symmetry of the shaft groove. Therefore, it is generally suitable for single piece production.
(2) Clamping with V-shaped frame: the clamping method of placing the cylindrical workpiece in the V-shaped frame and fastening it with a pressing plate is a common clamping method for milling the keyway on the shaft.
(3) Clamping with dividing head: clamp the workpiece with the two centers of the dividing head spindle and tailstock or with the method of one clamping one top of the three jaw self centering chuck and tailstock center. The axis of the workpiece is always on the connecting line between the center of the two centers or the three jaw self centering chuck and the rear center. The position of the workpiece axis does not change due to the change of the workpiece diameter, so the symmetry of the keyway on the axis will not be affected by the change of the workpiece diameter.
2. Adjustment of milling cutter cutting position (to the center)
In order to ensure that the keyway on the shaft is symmetrical to the axis of the workpiece, the position of the milling cutter must be adjusted so that the axis of the keyway milling cutter or the symmetrical plane of the disk groove milling cutter passes through the axis of the workpiece (commonly known as centering). Common adjustment methods are:
(1) Adjust the centering according to the cut mark: this method is the most commonly used method because of its low centering accuracy and simple use.
(2) Wipe the side and adjust the alignment Center: this method has high alignment accuracy and is suitable for occasions where the diameter of the disc groove milling cutter is larger or the keyway milling cutter is longer (relative to the workpiece diameter). When adjusting, first stick a thin paper on the side of the workpiece, start the machine tool, and make the rotary milling cutter gradually lean towards the workpiece. When the edge of the milling cutter rubs the thin paper, lower the workbench to exit the workpiece, and then move the workbench laterally for a distance to realize alignment.
(3) Adjust the centering with a lever dial indicator: this method has high centering accuracy and is suitable for vertical milling machines. It can adjust the centering of workpieces clamped with dividing heads, flat tongs and v-frames for clamping workpieces.
3. Milling method of keyway on shaft
(1) Milling the through keyway on the shaft: the through keyway on the shaft (such as the keyway on the plain bar of an ordinary lathe) or the half through groove with one end of an arc (such as the keyway on the milling cutter rod), which is generally milled with a disc-shaped groove milling cutter.
(2) Milling the closed keyway on the shaft: the keyway on the shaft is a closed groove or a half through groove with one end at right angles, which is milled with a keyway milling cutter. The common methods for milling the closed groove on the shaft with the keyway milling cutter are as follows:
A layered milling method: use a milling cutter that conforms to the width of the keyway to mill the keyway in layers. After installing the milling cutter, first try milling on the waste, check that the width of the milled keyway meets the requirements of the drawing, and then clamp, correct and center the workpiece before processing the workpiece.
B expanding milling method: first, use the keyway milling cutter with smaller diameter to carry out layered reciprocating rough milling, and then use the keyway milling cutter that meets the width of the shaft groove to finish milling. During finish milling, because the radial forces of the two cutting edges of the milling cutter can be balanced with each other, the deflection of the milling cutter is small, and the symmetry of the keyway on the shaft is good.