A 50 mm diameter bar is to be screwthreaded for 250 mm of it

A 50 mm diameter bar is to be screw-threaded, for 250 mm of its length, on a lathe. The included angle of the thread is 60 degrees, the pitch is 2.5 mm, and the outside diameter of the threaded portion is to be 50 mm. If the unreformed chip thickness is limited to 0.13 mm, how many passes of the tool will be required to complete the operation?

Solution

Included angle 60

Pitch 2.5 mm

Chip thickness limit – 0.13 mm

Total depth to go ap = pitch/2 * tan = 3* 2.5/2 = 2.165 (approximated value considering sharp points)

Maximum chip thickness = 0.13mm

First pass infeed = maximum chip thickness = apx maximum = 0.13

First pass infeed max = 0.13

X- number of passes

apx= ap × /(x–1)   ____      we know at first pass = 0.3

(x-1)= (ap/ apx)*= 2.165/0.13*0.55 =9.15

X = 83.8 +1 = 85 passes.