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 :
L_{1} = 182 × 4 = 728 mm
Now, the machining time (T) is given by following:
T = L_{1}/ feed × N
= 728 / (0.8 × 1.59)
= 5.72 minutes