What is a bevel gear?
Bevel gear is a type of gear in which the axis of rotation of two gears intersects with each other and the gear has a conical tooth-bearing surface.
Most of the bevel gears are generally mounted at right angles to each other (i.e they have the axis intersecting at 90° to each other). But some bevel gears can also be mounted at different angles as per requirements.
Bevel gears are used for power transmission between the shafts whose axis lies at some angle.
Bevel gears are used in various applications like automobiles, machinery, locomotives, power plants, etc.
Well, this was a short and simple introduction about bevel gear, but let’s now see the bevel gear generation process.
Bevel Gear Generation (How is Bevel Gear Generated?)
The teeth of the bevel gears do not have constant dimensions from the smaller to larger end.
Hence it is difficult to machine a bevel gear by using a rotary type cutter having fixed curves.
In simple words, the teeth of bevel gears cannot be formed, but they are generated instead.
So for generating the teeth on straight bevel gear, the two pitch cones are meshes together instead of meshing two pitch cylinders.
Straight bevel gear generation
The arrangement that is required for straight bevel generation is shown in the above image.
The gear blank (or the workpiece) is mounted on the arbor of the spindle and the cutter is mounted on the cradle (see above image).
The cradle as well as spindle rotates on their own axis, such that the rotation speeds are perfectly synchronised with the help of change gear trains.
The rotation movement of the cradle is converted into a reciprocating motion of the cutter.
The cutting action is performed by the cutter when it moves towards the apex of the gear cone (in the upward direction).
During the return stroke, the cutter is withdrawn from the blank to avoid damage to the machined surface.
In the very beginning of the operation, the cradle is set to the top most position and at a same time the gear blank is moved towards the cradle.
The cradle starts rotating and the cutter reciprocates downward as shown in the diagram.
By this motion of the cutter, one tooth is generated on the gear blank.
As shown in the below image, the two cutters represent only the single tooth space.
The complete cycle for bevel gear generation is shown in the above image.
First of all, the cutter cuts one of the sides of a tooth as shown in figure 1 and 2.
After this, the second tool (which is designed to cut the other side of the tooth) cuts the tooth surface and hence the complete first tooth is obtained at this stage (figure 3 and 4).
Now the cradle rolls further and the cutter reciprocates downward. During this stage, the cutter is withdrawn from the blank and the gear blank as well as cutter are reversed.
After this, the blank is indexed for the next tooth cutting (as shown in figure 5 and 6). In this way, the complete bevel gear is generated by repeating the operation for each tooth.
Gleason method for bevel gear generation
In Gleason method, the two disc type milling cutters are used for bevel gear generation.
This method of teeth generation is widely used for manufacturing small sized straight teeth bevel gears on a large scale.
The two cutters used in this method are mounted on individual spindles and they are inclined at the desired pressure angle.
When one tooth is cut, both the cutters are withdrawn and then the gear blank is indexed for the other tooth.
In this way, all the teeth are made on the blank.
This method is 2 to 3 times faster than the gear cutting by milling.