There are two basic types of milling machines- horizontal and vertical.� Horizontal are older.� Vertical machines grew out of drill presses and are more common today due to their great flexibility/versatility.
	A key milling parameter is whether one is up or down milling.� Up milling is so called because one the cutter enters the material at the �low� side of the cut and moves UP through the workpiece.� By contrast, in Down milling the cutter enter the workpiece at the �top� and moves DOWN into the workpiece.� Down milling is also called climb milling because it looks like the cutter is trying to climb the workpiece.� (Remember the terms by what the cutter is trying to do, DON�T be misled by our notion of Climbing Up things.)� One should notice that whether one is climb milling or up milling depends only on how one feeds the workpiece into the moving tool.� It is not dependent on cutter geometry, or what type of milling machine one is using.
	Up milling has the thickest chip at the END of the cut.� Thus, the thinnest chip is at the start of the cut.� At the very start of the cut, the cutter will be trying to take too thin of a chip.� (It�s like slicing anything- say for example deli meats.� In general any kind of a knife will do.� But if you want real thin slices, you need a super sharp cutter, like in the delis.� Even then there is a limit to how thin they can slice your bologna, roast beef, etc.)� So at the very start the up milling cutter does not cut, it deflects SLIGHTLY and rubs along the surface.� This builds up heat, and tends to wear the land on the relieved portion of the tool.� By contrast Climb milling starts the cutting where the chip is thickest and thus immediately enters the workpiece.� There is no rubbing thus the SURFACE FINISH is generally BETTER for CLIMB milling.� Further without the rubbing there is less heat and wear, thus climb milling allows for faster feeds and speeds and generally better tool life.� Finally, in climb milling the cutter action acts to secure the part.� So why is up milling called conventional .� If backlash is present climb milling can� pull the workpiece into the tool leading to an excessively deep cut- which can result in a fractured tool and is a dangerous situation.� (If an up milling cutter is sharper it cuts sooner/rubs less and gives better cut.� However its very rare for it to be sharp enough to do better than a climbing cutter, though Kalpakjian seems to note that it is possible.� In this class climb milling=better cut.)� If you don�t know how the machine will behave, it is safer (and as a general rule better) to use up or conventional milling.� If you are familiar with the machine, and know what sort backlash is to be expected, you may want to use climb (down) milling-- provided you are confident you can do it safely.� Most NC machines generally have much tighter control of backlash (ball screws, etc.) and can handle down milling.� On hand operated machines, large backlashes can be present.� You should be careful about using down milling in these cases.
	To repea,t while down milling often produces better cuts (and longer tool life), up milling always works, and will not result in a dangerous situation.� If you are not sure which to use, use up milling for safety.