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Machinability Tool Factors

Manufacturing & Design

The term machinability refers to the ease with which a metal can be machined to an acceptable surface finish. Materials with good machinability require little power to cut, can be cut quickly, easily obtain a good finish, and do not wear the tooling much; such materials are said to be free machining. The factors that typically improve a material's performance often degrade its machinability. Therefore, to manufacture components economically, engineers are challenged to find ways to improve machinability without harming performance.

Machinability can be difficult to predict because machining has so many variables. Two sets of factors are the condition of work materials and the physical properties of work materials.

The Machinability Factors, Cm 

Common Workpiece	Cm at w / D ratios:
Materials	w/D < = 0.5	0.5 < w / D < 0.7	w/D = (0.7-1.0)
Carbon and alloy steels	1.0	1.3	1.5
Stainless and tool steels	1.6	1.8	2.2
Gray cast iron	2.1	2.6	3.1
Ductile and malleable cast irons	1.0	1.3	1.5
Titanium alloys	1.0	1.5	1.7
Heat-resistant alloys	1.6	1.8	2.2
Aluminum alloys, s < = 70,000 psi*	0.7	0.8	0.9
Aluminum alloys, s > 70,000 psi	0.8	0.9	1.0
Copper alloys, s < = 70,000 psi	0.8	0.9	1.0
Copper alloys, s > 70,000 psi	1.0	1.3	1.5

Milling	Depth of cut	Feed per tooth		Cw
Category	(min-max), in.	(min-max), in.	A * , in2
Light	0.020-0.100	0.003-0.006	<= 0.0006	1.1
Medium	0.100-0.200	0.006-0.010	<= 0.002	1.2
Heavy-duty	0.200-0.400	0.010-0.020	> 0.002	1.3

Machine Efficiency Factors, E

Type of Drive		E, %
Direct Drive		95
Direct Belt Drive		90
Back Gear Drive		75
Geared Head Drive		70-80
Oil - Hydraulic Drive		60-90