Hereinafter referred to as the schematic image of the most common shapes and proportions and some brief comments that may be useful in the choice of one of these shapes.
1 Common pinion
The most economic version (material and workmanship), admits to milling multiple pinions in one set-up.
2 & 3 Pinions
With protruding hub: the nave is protruded or shifted for the pinions with a narrow facewidth or for moving the gears compared to the mounting place..
4 & 5 Pinion shafts
Used when the difference of the tooth foot diameter of the shaft is too small to allow a normal keyway on the shaft, avoids the use of a key. To note that the centres of the shaft should be extremely cared for in order to admit a concentric milling.
6 & 7 Common wheels
With membrane or with spoke wheels: for wheels of medium dimensions without excessive facewidth. The wheel with membrane, fully turned, practically assures a good balancing. The wheel with spoke wheels gives a maximum resistance for minimum weight.
8 Wheel with spokes in H-shape
Applied for transfer of large powers which require a large facewidth.
9 & 10 gear ring with external gear
Toothed elements that can be centred and secured on a wheel body of other material or on a pulley or on a special hub mounting by means of bolts or by shrinking.
11 & 12 Wheels and gear rings with internal gears
Are chosen to ensure a bigger engagement length (several teeth) or to achieve a different sense of shaft rotation. For the wheels, a milling extension with a minimum of 5 mm has been foreseen.
13 & 14 wheels of welded version
To compare with the shapes 6 & 7 and 8.
15 Composite wheels for herringbone teeth or double helix teeth
Applicable for transfer of very large powers which require a large facewidth and a double helical teeth (avoidance of adverse axial loads) or when the gear rings for reasons of resistance should be of forged alloy steel, when standard wheel bodies of cast iron, cast steel or just welded steel are sufficient.
16 & 17 Cylindrical worms
Same note as for pinions 1 to 5.
18 & 19 Worm wheels
Figure 18 shows a composite wormwheel with a bronze ring gear and wheel body of cast iron or cast steel; this solution allows to limit the weight of the bronze and the replacement of the toothed part, in case of wear, easy and more economical to realize.
Figure 19 shows a common wormwheel (with membrane or spokes) for versions in cast iron, bronze or aluminum. The shape of the rim is simpler (thus more economical) than that of figure 18.
20 to 25 Bevel gears
The choice of shape for bevel gears is based on the possibilities or need for mounting. As for the cylindrical pinions and wheels the implementation may take the shape of regular discs, pinion shafts, wheels or crowns. As much as possible, avoid a protruded hub, i.e. the root cone should be free up to the tip cone.
26 to 28 Double pinions
When two or more teeth must be manufactured on one and the same piece (double, triple pinions) necessarily an adequate separation must be provided between the gears in order to ensure a milling extension. For straight teeth usually an extension of 5 mm is sufficient (tooth hobbing with pinion or rack type cutter, maximum module 12.7); for heavier teeth with hob implementation the extension groove should be about 5 x the module.