How to choose a flat key? Is a round head or a flat head better?

Many people use flat keys, and our national standard GB/T1096 for ordinary flat keys specifies three different types of flat keys, namely Type A (double round head), Type B (flat head), and Type C (one end round head and one end flat head).

But I don't know if you have any questions when choosing: what is the difference between a round head and a flat head? How should I choose in practice? In fact, there is not much difference between the two types of keys. When the material is the same, the cross-sectional size is the same, and the effective length is the same (the roundhead key needs to subtract the half circle size at both ends), the bearing capacity of the two types of keys is the same. But there are still some differences that need everyone's attention. Let's take a look together.

There are differences in the machining methods of the keyways corresponding to the two keys. The keyway of a round headed key can usually only be machined using an end milling cutter, while the keyway of a flat headed key can be machined using either a disc milling cutter or an end milling cutter. As shown in the following figure. The stress concentration at the end of the keyway processed by disc milling is smaller than that of end milling.

2. The round headed key is more convenient to install than the flat headed key, and the semicircular part can help align the key in the shaft keyway and play a guiding role.

3. The round head key usually cannot move axially in the keyway and is not easy to loosen, so it is not necessary to fix the key in position with fixing screws; When the length of the keyway is longer than the length of the key, it is best to fix it with screws if it is expected to remain in a fixed position.

4. Round headed keys are pre made to a certain length and can be used directly, but inventory management is difficult when there are multiple size specifications. The flat head key can be cut according to the required length on the basis of a long key, but there are additional operations such as measurement, filing, or polishing.

In places with high requirements for rotational dynamic balance, flat headed keys are usually used. The round head key will extend beyond the hub at both ends while ensuring that the effective key length is the same as the hub; When the overall length is the same as the width of the wheel hub, it is always difficult to adjust balance due to the material gaps at the wheel hub due to the rounded ends at both ends.

6. The right angle positions at both ends of the flat head key are prone to generate significant compressive stress on the side of the shaft keyway, which can cause damage to the shaft, while the round head key is much better.