Meccano Gears - 6 - Contrate Gears

Meccano Gears - 6

Contrate Gears

Contrate gears are not normally used in modern applications, their place has been taken by bevel gears. However, many Meccano sets have contrate gears, the large 50 tooth (Part 28 as shown here) or smaller 25 tooth (part 29) gear.

These gears are used in Meccano because they produce a 90 degree drive with both shafts on the same plane. Additionally, they can be meshed with any Meccano pinion giving a potential wide range of ratios. The different pinion diameters are accommodated simply by moving the contrate gear position on the shaft.

The large 50 tooth contrate can give a range of ratios :-

13 tooth pinion (part 26r) 50/13 = 3.85:1
15 tooth pinion (part 26d) 50/15 = 3.33:1
19 tooth pinion (part 26) 50/19 = 2.63:1
25 tooth pinion (part 25) 50/25 = 2:1

The smaller 25 tooth contrate gives the following ratios :-

13 tooth pinion (part 26r) 25/13 = 1.92:1
15 tooth pinion (part 26d) 25/15 = 1.67:1
19 tooth pinion (part 26) 25/19 = 1.32:1
25 tooth pinion (part 25) 25/25 = 1:1

The contrate gear has two more tricks up its' sleeve, you can use a pair of gears engaging face to face as a positive clutch, only suitable for low load and  stop / go applications, as there isn't any margin for slippage as with a conventional friction type clutch.

Finally, because the meshing shaft centreline just needs to pass through the centreline of the shaft of the contrate gear, it can effective mesh at any angle. If you think of the contrate gear as a clock face, the meshing shaft can exit the clock face at any point, as long as the shaft passes through the centre.

There is one variation of this part available as a reproduction. This is :-

29a - 19 Tooth Contrate Gear - This is a small diameter contrate, to give a different set of ratios.