Page 205 - Mechanical Engineer's Data Handbook

MANUFACTURING TECHNOLOGY 193

Power 5.7.3 Surface finish

kdfv
Turning: P=- Different processes produce different degrees of finish
moo0 on machined surfaces. These are graded from N1 with
Drilling: T= k,fo.75D1.8 an average height of roughness of 0.025 pm, up to N12
roughness 50pm. The manner in which a machined
2nN T surface is indicated is shown.
p=-
6ooo0 a+b+c+. . .
Average height of roughness, h, =
Milling: P = - L
kMdwfm
60 -where a, b, c, etc. =area on graph, and L =length of
surface.
Volume of metal removed
Turning: V = dfv
ZD2j7V
Drilling: V=-
4Ooo

wdfM
Milling: V=-
lo00

Roughness grade N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12

h,(pm) 0.025 0.05 0.1 0.2 0.4 0.8 1.6 3.2 6.3 12.3 25 50
Finishing processes Surface indication

Mill Ream
Bore Broach
Turn Lap
Grind Hone, etc.

5.7.4 Merchants circle for tool forces The diagram can be drawn to give:
F, =shear force
‘Merchant’s circle’ is a well-known construction for F, = resultant force
the analysis of cutting forces for a single-point tool. If F=friction force on tool face
the cutting and feed forces, the initial and final chip F,, = force normal to shear force
thickness and the tool rake angle are known, then the F, =force normal to F
other forces, friction and shear angles can be found. p =coefficient of friction = F/F,
Known: 6 =friction angle = tan - p
F, =cutting force 4 = shear angle
F,=feed force
t, =initial chip thickness
t, =final chip thickness
a = tool rake angle