Machining refers to the process of shaping metal by removing the unwanted material from it. This process can be performed in a variety of ways. There are many different machining processes, including drilling, turning, and milling.

Drilling uses a rotary cutting tool, the drill bit, to cut a hole in the material. The drill bit presses against the metal while being rotated very quickly in order to create a circular hole.

Turning uses a lathe to rotate the metal while a cutting tool moves in a linear motion to remove metal along the diameter, creating a cylindrical shape. The cutting tool can be angled differently to create different shapes. It can be done manually or with a CNC turning machine. CNC machining is generally used when part measurements must be extremely precise.

Milling is the process of cutting and drilling material. A milling machine, regardless of whether it’s operated manually or through CNC, uses a rotating cylindrical tool called a milling cutter. It is held in a spindle and can vary in form and size. The main difference between a milling machine and any other drilling machine is the ability to cut in different angles and move along different axes.

5-axis machining refers to a machines ability to move a tool or a part in five different axes simultaneously. Basic machining operates on three primary axes, X,Y and Z; however, a 5-axis CNC machining tool can rotate two additional axes, A and B, which give the cutting tool a multidirectional approach. In other words, thanks to multi-axis machines, turning, freezing and milling are done on the same machine.

Manufacturing Process	Roughness Average (Ra)
	Micrometers (Micro-inches)
Forming Processes	50 (2000)		25 (1000)		12.5 (500)		6.3 (250)		3.2 (125)		1.6 (63)		0.80 (32)		0.40 (16)		0.20 (8)		0.10 (4)		0.05 (2)		0.025 (1)		0.012 (.5)
Sand Casting
Hot Rolling
Forging
Permanent Mold Casting
Investment Casting
Extruding
Cold Rolling, Drawing
Die Casting
Metal removal or cutting processes	50 (2000)		25 (1000)		12.5 (500)		6.3 (250)		3.2 (125)		1.6 (63)		0.80 (32)		0.40 (16)		0.20 (8)		0.10 (4)		0.05 (2)		0.025 (1)		0.012 (.5)
Flame Cutting
Snagging
Sawing
Planing, Shaping
Drilling
Chemical Milling
Elect Discharge Machining
Milling
Broaching
Reaming
Electron Beam
Laser
Electro-Chemical
Boring, Turning
Finishing processes	50 (2000)		25 (1000)		12.5 (500)		6.3 (250)		3.2 (125)		1.6 (63)		0.80 (32)		0.40 (16)		0.20 (8)		0.10 (4)		0.05 (2)		0.025 (1)		0.012 (.5)
Barrel Finishing
Electrolytic Grinding
Roller Burnishing
Grinding
Honing
Electro-Polish
Polishing
Lapping
Super Finishing
	50 (2000)		25 (1000)		12.5 (500)		6.3 (250)		3.2 (125)		1.6 (63)		0.80 (32)		0.40 (16)		0.20 (8)		0.10 (4)		0.05 (2)		0.025 (1)		0.012 (.5

This chart shows the surface roughness capacity of various Manufacturing processes. The values are shown with a typical range and a less frequent range for each manufacturing process. In machining process, the averange range is 0.8Ra. In order to have less roughness, the manufacturer has to use special finishing techniques. That’s why lower surface roughness means higher costs.

Surface Roughness Ra (um)	25.00	12.50	9.12	6.25	5.00	3.75	2.50	2.12	1.80	1.60	1.32	1.00	0.80	0.45	0.32	>0.20
Tolerance +/- (mm)	1.00	0.60	0.35	0.25	0.20	0.15	0.10	0.08	0.06	0.05	0.04	0.03	0.02	0.02	0.01	<0.005

The charts above show the relationship between Tolerance and Surface Roughness. To achieve lower surface roughness, the tolerances must be tigher. Basically the finer the finish and the tigher the tolerance the greater the cost. Because both surface roughness and tolerance are inversely propotional to cost.