Which Meccano Gears Mesh Together?
All standard Meccano gears are based on the same tooth profile called 38DP. This means that any Meccano gear will mesh with any other Meccano gear, however, the spacing may not be a multiple of ½" (standard Meccano hole spacing) or the angle of the gears may not be parallel or at 90 degrees. Gears with other tooth profiles (sizes) are available, both the larger tooth sized 16DP which is used on the geared quadrants (167a) and its' associated gear (167c), and 20DP which is used on some special large gears. The table below relates to the standard 38DP gears, with standard Meccano spacing at multiples of ½". To see which non-standard gears mesh at standard spacing, check the details of each individual gear in the catalogue.
Meccano Standard 38DP Gear Meshing Table
If you are using a non standard spacing (ie other than multiples of ½"), then you can mesh other pairs of gears. To calculate the meshing distance in inches, count the teeth on both gears, and divide by 76 (38DP x 2).
Contrate gears may be adjusted on the axle to mesh with any spur gear from 15 to 38 teeth, giving a large variety of possible ratios.
Right Hand (RH) or Left Hand (LH) Helical gear pairs (211a, 211b) will mesh at 3 hole spacing (1" centres) at 90 degrees to give a 2.5:1 ratio. A RH and LH Helical gear will mesh in parallel (like standard gears). This gives a greater tooth contact area for a given gear width, as the teeth are cut at 45 degrees to the face of the gear. This will enable these gears to take a higher load.
There is more information on gear meshing on the blog page.