Estimate the Machining Time

A hollow workpiece of 60 mm outside diameter and 150 mm length is held on a mandrel among centers and turned all over in 4 passes. If the approach length = 20 mm, over travel = 12 mm, average feed = 0.8 mm/rev., cutting speed = 30 m/min, estimate the machining time.

Solution

We know that,

Cutting speed = π DN /1000

or,         30 = ( 60 × π N )/1000

N = 159 rpm

 Now, the total (length) traveled by the tool in a single pass in given by :

L = 150 + 20 + 12

= 182 mm

Therefore, the total length traveled by the tool in its 4 passes is given by :

L₁ = 182 × 4 = 728 mm

Now, the machining time (T) is given by following:

T =       L₁/ feed × N

      =    728 / (0.8 × 1.59)

      = 5.72 minutes