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List pairs of gears that
can be combined to give
the required gear ratio
This shows a list of compound gears that can be used to produce any gear ratio. You can enter the gear ratio as a decimal number or a fraction with / .
Enter the gear ratio you require in the box below.
The default is 1.27 for converting between imperial and metric. This is used because 1.27 * 2 = 2.54 which is the conversion factor. Please see the extensive discussion of these ratios in the help file (blue button above).
I have derived a general equation for calculating the gear ratio required for conversion between metric and imperial. The same pair of gears can be used for conversion from metric to imperial or from imperial to metric. You just flip the pair of gears over which inverts the ratio.
The equation is independent of the gearbox. It does not need to include any gearbox ratios.
The general equation is:
R = 25.4 / ( Li * Lm )
Lm is the pitch of the desired metric leadscrew, and
Li is the TPI of the imperial leadscrew.
eg if you want to make an imperial lathe with an 8TPI leadscrew behave like a metric lathe with 3mm pitch leadscrew the ratio is:
R = 25.4 / ( 8 x 3 )
R = 25.4 / 24
R = 1.05833333
Enter This ratio in the INPUT box below.
TABLE OF GEAR RATIOS FOR CONVERTING BETWEEN METRIC AND IMPERIAL
by Evan Lewis for the free online calculator 'RideTheGearTrain.com'
Table of Ratios:
If you have an imperial lathe, look across the top row to find the column which matches the TPI of your leadscrew. Look down the left column and decide which leadscrew pitch (in mm) that you would like your lathe to produce. Find the ratio where the row and column meet. Copy and paste this ratio into the INPUT box below.
If you have a metric lathe, look down the first column to find the mm pitch of your leadscrew. Look across the top row and decide which leadscrew TPI that you would like your lathe to produce. Find the ratio where the row and column meet. Use copy and paste to use this ratio in the INPUT box below.
The program on this page will list all the pairs of gears that approximate the ratio you requested, and the amount of error that is introduced. This error is caused by the fact that the number of teeth on any gear must be an integer.
The program allows you to enter the ratio e.g. 1.27 or any fraction containing a "/" as in 127/120.
Finally, any gear combination you choose can be tested in gear train calculator by entering the chosen gears in Step 2B in the main menu. You can use automatic mode and put all the gears in the list of change gears, along with any other gears you have. The program will mix and match all the gears.
Otherwise, if your lathe does not allow you to mix gears in this way you cannot use automatic mode, and enter the compound gears in a separate list. In the list of compound gears you can enter them as separate gears eg 127, 100 which can be mixed with other gears in the compound list, or if the gears are joined together permanently and cannot be separated enter the pairs like this 127/100.
Other uses for compound gears include the ratio Pi=3.14159 for modulus and diametric pitch which could be approximated by 22/7.
This function does not use any of the lathe data you entered above for gear train calculations!