Metalcuttingfor

the Non-metalcutting Professional

History The lathe is an ancient tool, dating at least to the Egyptians and, "known and used in Assyria, Greece, the Roman and Byzantine Empires."

The earliest depiction of a lathe comes from a Ptolemaic tomb painting.

began the changeover from wood-working lathes to ones capable of machining tool steel

The first satisfactory screw-cutting lathes were made by an English instrument maker, Jesse Ramsden in 1770

It was not until the late 17th Century that clockmakers, builders of scientific instruments, and furniture and gun makers

His efficient methods, especially the use of interchangeable parts, revolutionized the small-arms industry, and gradually these production methods were applied to most types of manufacturing.

In 1818 Eli Whitney built his first milling machine, or mechanized cutter, which precisely shaped metal parts.

A metal lathe usually spins, or “TURNS” the workpiece along a horizontal axis. A mandrel or chuck

is mounted to the headstock of the lathe. A follower block or tail block is mounted to the tailstock. The

cutting tool is FED into the spinning material to cut it.

What the difference between a mill and a lathe?

What the difference between a mill and a lathe?

The cutting tool remains stationary (except for its

rotation) while the workpiece, FIXTURED to the table of the

machine moves to accomplish the cutting action.

This is a picture of a “Knee Mill”

In a milling machine the part is held in a FIXTURE

or some sort of WORKHOLDING device.

Prior to the introduction of computers each Knee Mill required an operator manually controlling the speed of the spindle and movement of the table. Note that there is on one tool in use and the operator has to stop the machine to change the drill from one size to another

One Operator = One Tool = One Machine

The birth of the MACHINING CENTER

A CNC (computer numerically controlled) Machine has many benefits. Pictured here is a CNC Vertical milling machine

The movement of the machine is controlled by the computer.

The operator now can program multiple machines to run unattended and use multiple tools

THEN NOW

THEN: Many machinesMany operators

Doing JUST one operation

NOW:One MachineOne OperatorDoing MANY operations

TolerancesAs time has passed tolerances that parts are made to have gotten “tighter” In other words, smaller and smaller.The “fit” between two parts is “closer”

This is now measured in MICRONS

Human Hair 0.0035

inch 0.0889 mm

Micron 0.000039 inch 0.001

mm

How Big is a Micron ?

Basically, it all comes down to time. The shorter the time to set up a part, cut a part, remove a part and reload the raw material is critical. As you can already tell CNC’s have reduced the labor force requirements.

The NEXT BIG THINGMachine tools that combine milling, turning and other processes on a single platform go by many names.

“Turn/mill”, “Integrated mill turn center” and “multitasking” are the most common labels.

The name reflects the design philosophy behind these machines.

They are intended to provide the full turning capability of a pure turning center along with the full milling capability of a pure machining center.

The combined capabilities can be used for completing complex workpieces in one setup.

Mill-Turn Machines

Understanding WORKHOLDING

Originally, manufacturing was based upon one man holding one part on the table and making the part complete to the specifications.

Typically this was done in a single station vise:

One Vise: One workpiece

With the advent of CNC Milling machines it became more efficient to hold more parts and do as many operation as possible in one set-up

Other types of fixtures:

Three jaw milling chucks for holding round parts:

Other types of fixtures:

Magnetic Vises which permit cutting tools to mill around the all sides of the part

Its basic form is that of a rotating cutter or endmill which rotates about the spindle axis (similar to a drill), and a movable table to which the workpiece is affixed.

A milling machine is a power-driven machine used for the complex shaping of metal (or possibly other materials) parts.

That is to say the cutting tool generally remains stationary (except for its rotation) while the workpiece moves to accomplish the cutting action.

Milling machines may be operated manually or under computer numerical control

Milling is generally done on a milling machine, which is a power-driven machine used for the complex shaping of metal (or possibly other materials) parts, by removing unneeded material to form the final shape

Its basic form is that of a milling cutter that rotates about the spindle axis (like a drill), and a worktable that can move in multiple directions (usually three dimensions [x,y,z axis] relative to the workpiece,

whereas a drill can only move in one dimension [z axis] while cutting.

Milling machines may be operated manually or under computer numerical control (CNC), and can perform a vast number of complex operations, such as slot cutting, planing, drilling and threading, rebating, routing, etc.

The motion across the surface of the workpiece is usually accomplished by moving the table on which the workpiece is mounted, in the x and y directions.

A tool bit generally refers to a plain High Speed Steel (HSS) tool used for turning work in lathes.

Originally, high carbon steel was used with the appropriate hardening and tempering.

This material has been replaced with HSS due to its improved properties, and it usually takes the form of a simple square bar.

The cutting edge is ground to suit a particular machining operation and may be resharpened or reshaped as needed.

The ground tool bit is then held solidly by a tool holder while it is cutting

Materials like carbide, ceramics like cubic boron nitride, and diamond all allow faster material removal than HSS.

Not all tool bits are HSS.

Because these materials are expensive and hard to work with typically the body of the cutting tool is made of steel, and a small cutting edge made of the harder material is attached.

The cutting edge is usually either screwed on (in this case it is called an insert), or brazed on to a steel shank (this is usually only done for carbide).

First of all, at the very high cutting speeds and feeds supported by these material, the cutting tip can reach temperatures high enough to melt the brazing material holding it to the shank.

Almost all high performance cutting tools use the insert method. There are several reasons for this.

Economics are also important: with inserts they are made symmetrically so that when the first cutting edge is dull they can be rotated, presenting a fresh cutting edge.

There are many types of inserts: some for roughing, some for finishing. Others are made for specialized jobs like cutting threads or groove

Some inserts are even made so that they can be flipped over giving as many as 6 cutting edges per insert.