Determine the transformation ratio (TR) of the gear train

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Determine the transformation ratio (TR) of the gear train connecting the spindle and the lead screw of 4TPI required to cut 1.0 mm pitch screw threads in a centre lathe.

1. 20/127
2. 20/126
3. 20/125
4. 20/120

Correct Option: A

Transformation ratio = train value
= pitch of job threads/pitch of lead screw threads
= 1.0 mm/(1/4 inch) = (1.0 × 4)/(127/5)
= 1 × 4 × 5/127 = 20/127. (The them 127/5 is used for converting inches into mm).