Milling keyways / splines CNC

The keyed connection is one of the basic ways of placing the hub on the shaft journals. For this purpose, a specially prepared key is used, which is placed in the groove made. The grooves are made in both the hub and the shaft of elements joined by means of milling. Milling keyways, channels with specific parameters can be done in different ways, depending on the geometrical features of the groove. Key joints should be made in accordance with accepted standards for geometric tolerances and surface roughness, e.g. DIN 6885-1.
Splined connections are characterized by the possibility of greater load and allow centering of connected elements in relation to keyed connections. One of the methods of making the spline is its milling spline can be performed both on lathes with a C and Y axis or on multi-task machines also milling machines with a divider are suitable for it. Splined shafts are made of hardened steel, cast iron or cast steel.

Milling at keyed joints

The first way to mill a keyway involves the use of standard end mills. With the help of this type of tool we will make keyways with closed (blind) geometry, with dimensions larger than the tool diameter. Technically correct is the platform in which the machining is divided into two stages: roughing and finishing. The main advantage of this approach is the high accuracy of the groove made. Roughing is characterized by the need to determine the method of entry of the tool into the material, e.g. oblique insertion, as well as to define the path profile. You can use trochoidal milling that allows you to quickly remove material, leaving only the allowance for the final achievement of the assumed keyway profile. The use of a long-edge milling cutter that allows for efficient volumetric milling, in combination with the technology generating trochoidal paths enables the efficient milling of difficult-to-cut materials such as titanium, heat-resistant steels, as well as steels with curing coatings.

The second stage is the final obtaining of the keyway geometry. A correctly defined technological process containing adapted machining parameters to the tool used allows to obtain keyways in the specified standards. Obtaining the assumed shape and dimensional tolerance is possible by using a small radial depth of cut, eliminating the tendency of the cutting tool to vibrate, as well as to deviate from the milling axis. The second way to make a groove concerns the possibility of using circular cutters. Depending on the characteristics of the groove, we are able to make long and relatively deep countersinks using a circular tool, and we can also adjust the width of the pickup. By giving a tolerance in the technological documentation of the groove, we can divide the machining depending on the accuracy of the execution and type of machining in the same way as when using milling cutters, e.g. roughing and finishing groove milling. We will make all kinds of through grooves using disc milling cutters. Depending on the semi-finished material used, these tools can be used for concurrent and counter-rotating milling.

The third way to implement keyways (or splined) is to use machining centers, both milling and turning, and to use special attachments that allow chiselling. The whole process is very similar to the standard version with the help of slotting machines. The machining cycle involves the entry of an immobilized single-edged tool into the workpiece (shaft, sleeve), then a hole in the material with a full cross-section of the cut layer and retraction of the tool in the workpiece axis with the insert of the cutting plate into the groove. The next layer is cut with the given tool offset. The shape of the groove depends on the profile of the cutting insert mounted in the tool holder and gives great flexibility. The use of the Z-axis tool descent for a vertical milling center with a centrally mounted workpiece and simultaneous rotation on the C axis allows for a groove with a helical surface. The method allows external and internal grooves. The main advantage of the chiselling method is the possibility of obtaining very high dimensional and surface accuracy of the keyway groove.Lack of the required manufacturing tolerance may negatively affect the entire key connection. The occurrence of excessive slack in the case of heavily loaded connections leads to breaking of the grooves and significant wear of the inlets. In this case, the connected parts have a tendency to unwanted vibrations and rapid wear of the device, which is why it is so important to choose the right method, tools and technological process.

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