Gears are available in DP i.e. inches and Module i.e. Metric/mm...
As per DP or Module, both are the same just measuring units are different. So if you ordered the gears in dp then just multiply it by 25.4 which gives you the Module (size of that gear in metrics).
To know the selection of gears you need basic knowledge of its parameters and formulas.
1) Pitch Circle Diameter.
2) Outer Diameter
3) Inner Diameter
4) Pressure angle
5) Addendum and Dedendum
6) Bore Keyway
7) Backlash
8) Clearance
9) Tooth Profile
Nomenclature of Spur Gears: - 1M - 15T - 6 - 15
[ Module(M) = 1 No. of teeth (Z) = 15 Internal Diameter (ID) = 6mm PCD = 15mm ]
For module (M) = PCD/T & For DP = T*25.4/PCD
So, Procedure is as follows with example,
Requirement 27T and dia70 to dia90 approx.
Solution: -
In the catalogue 8DP gives 27T and nearby value of diameter is
PCD = 27*25.4/8 = 85.725 OR DP-8 TEETH-27 PCD-85.725 (In the catalogue)
Also, you can check DP or Module conversion value.
For Ex. DP-8
In Module (M) = 25.4/DP = 25.4/8 = 3.175. (So, DP = 8 / M= 3.175 Both are same)
For Ex. M-1.5
In DP =25.4/M = 25.4/M = 25.4/1.5 = 16.933. (So, M=1.5/ DP= 16.933 Both are same)
Relief Angle have different types such as 14.5 or 20 in degree
From above you learned that Module or DP conversion for gear purchase.
Now, if we need module 4 gear and a ratio of 5:1
we need greater than 520 OD So, PCD = M (Module) x Z (No of teeth) = 4 x 130 = 520 mm
and now for pinion we take PCD = M (Module) x Z (No of teeth) = 4 x 26 = 104 mm
Gear ratio will be Z2/Z1 = 130/26 = 5 would be a good example.
Same if you need in DP so,
Convert DP into Module i.e. DP = 25.4/M = 25.4/4 = 6.35
During purchase 6.35DP 130T & 6.35DP 26T
