Key and keyway are generally used for the mechanical connection. In the machining process of mechanical parts, lots of long shaft parts are designed with multiple keyways, which generally has strict requirements in dimensions and tolerance, as well as the angle between keyway, or keyway and positioning reference hole. Ordinary marking method can’t reach the needs, meanwhile, due to the poor rigidity of shaft parts, this type of component needs to be processed on CNC milling machines. How to cut a keyway on a milling machine? In this article, we’ll introduce what is keyway milling, the basics of key and keyway, methods of milling keyway, as well as cutters of the operation.
Keyway milling is the process of producing a keyway using the milling machine. Key refers to a type of part used in mechanical transmission, mainly for the circumferential fixation between the shaft and the parts on the shaft to transfer torque. Some keys can also realize the axial fixation or axial movement of the parts on the shaft. The groove or slot machined for installing the key is called keyway, which is usually cut along the axis of the cylindrical surface of a shaft. When you put a pulley on a shaft, the keyway can prevent the pulley from rotating on the shaft. The keyway can be divided into open type, semi-open type, and closed type.
The keyway milling operation can be done either on a specialized keyway milling machine or ordinary mills. When machining on the keyway milling machine, the workpiece is clamped by the fixture, and the keyway milling cutter is used to mill it layer by layer.
1. Clamping and calibration of the workpiece
When clamping the workpiece, not only the stability and reliability of the workpiece should be ensured, but also the central position of the clamped parts should not be changed, that is to ensure that the centerline of the keyway coincides with the axis line. Milling keyway clamping methods generally have the following several.
(1) Use parallel-jaw vice
Installation with machine vice is suitable for milling keyway on small and medium-short shafts. When the diameter of the workpiece changes, the center of the part changes in the jaw, which affects the symmetry and dimensions of the keyway. But it is simple, stable and suitable for single-piece production. If the outer circle of the shaft has been finished, this clamping method can also be used for mass production.
(2) Use v-shaped frame
The V-shaped frame clamping is suitable for milling the keyway on the long and thick shaft. The advantages of V-frame positioning and support are good clamping stiffness, convenient operation and easy alignment of the milling cutter. The center of the workpiece is only on the bisector of the V-shaped iron, and it varies with diameter. Therefore, when the center of the milling cutter is aligned with the bisector of the angle of the V-shaped iron, the symmetry of the keyway can be ensured.
(3) Use T-slot
Put the shaft on the T-sot of the milling machine worktable, and clamp the piece with the plate directly. When machining long shafts with diameters ranging from 20 mm to 60 mm, they can be directly clamped on the T-slot of the worktable. However, this method is not suitable for stepped shafts and large-diameter shafts.
(4) Use index head
If it is the installation of a symmetric key and multi-slot workpiece, in order to make the position of the keyway on the shaft accurately distributed, the dividing head or fixture with an indexing device is mostly used. When the workpiece is clamped by the three-jaw self-centering chuck and the back center of the dividing head, the workpiece axis must be on the axis line between the three-jaw self-centering chuck and the center, and the position of the workpiece axis will not change with the change of the diameter. Therefore, the symmetry of the keyway on the shaft will not be affected by the change of the workpiece diameter.
2. The selection of keyway milling cutter
In the process of milling keyway, the requirement of choosing a milling cutter is strict, which directly affects the precision and surface roughness of keyway. In general, milling open keyway is done with disc milling cutter; milling closed keyway is often using end milling cutter and keyway milling cutter. When milling with an end mill, a hole with the same diameter as the milling cutter should be drilled at one end of the groove bottom, and the depth is the groove depth. The selection of milling cutting tools will affect surface roughness and productivity. Milling tools recommended for different keyways:
(1) Shaft keyway for woodruff key: woodruff keyslot milling cutters
(2) Square-end keyway: plain milling cutter or side milling cutter
(3) Round-end keyway: end milling cutters
3. Adjust the cutting position of milling cutter
In keyway milling, it’s critical to adjust the related position of the cutter and parts, and make the rotation axis of the cutting tool is aligned with the axis of workpiece.
4. Milling of keyway
1) Layered milling
Layered milling is to cut the keyway layer by layer, the depth of each operation is only 0.5-1 mm, then carry out the back and forth milling with a larger feed rate until it reaches the desired depth. The advantage of this method is that if the milling cutter is blunt, it only needs to grind the end face, and the milling cutter diameter is not affected; however, when processing on the ordinary milling machine, the operation flexibility is not good, and the production efficiency is lower than the normal cutting.
2) Expand milling
Grind the selected keyway milling cutter until its outer diameter is reduced by 0.3-0.5 mm (keep a good cylindricity), when milling, leave 0.5 mm allowance at both ends of the keyway, move the cutter back and forth for milling, and then measure the groove width to determine the width allowance. Use a milling cutter that conforms to the size of the keyway to continue milling both sides of the keyway to the desired size, and mill to the required length of the keyway at the same time. The roundness of the circular arc at both ends of the keyway shall be ensured during milling. This kind of milling method is easy to make the groove side have a slope.