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Machining Tool Forces
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There are three forces acting on a cutting tool

Forces Graph

  Axial

Tangential 

Radial

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When three forces are present during a cutting operation it is called Orthogonal Cutting.

When two forces are present during a cutting operation it is called Oblique Cutting.

The Forces Graph indicates the relative sizes of the forces present during a typical cutting operation.

Cutting Tool angles are important and a comparison can be made between this an the action of a knife peeling an apple. It is easier for the knife to cut "slide" through an apple if the wedge angle is kept small

 

Forces Graph

wpeA.gif (2772 bytes)  

  • The  graph indicates that the three forces Tangential, Radial & Axial are different.

  • The largest force is Tangential which tends to deflect the tool.

  • The Axial force is next and this resists movement of the cutter towards the chuck

  • The smallest force is Radial and can be greatly reduced by keeping the plan approach angle small.

 

Tangential Force

Tangential.gif (3077 bytes)

  • The largest force is Tangential which tends to deflect the cutting tool downward.

  • The reason it is called Tangential is that it acts along a line which is a tangent to the work as indicated.

  • The Tangential force is usually the greatest of the three.

  • The cutter must be strong and held securely to resist breaking as a result of this force.

 

Radial Force

Radial.gif (2635 bytes)

  • The smallest force is radial and can be greatly reduced by keeping the plan approach angle small.

  • The cutter must be strong and held securely to resist breaking as a result of this force.

  • The reason it is called radial is that it acts from the centre of the work towards the cutter  as indicated.

 

Axial Force

Axial.gif (2584 bytes)

  • The Axial force   acts parallel to the axis of the work-piece.

  • It  resists movement of the cutter towards the spindle.

  • This axial force is usually less than the tangential force.

  • This can be reduced by keeping the feed rate low.  

 

Cutting Tool Angles

A constant compromise is taking place when deciding the correct angles for a cutting tool. The angles are dependent mainly on the type of material being cut and the shape of the material. In general it is best to keep the Wedge angle as large as possible but good cutting will not take place without having sufficient rake and clearance.

The Wedge or Tool angle. This is the visible angle when we look at any cutting tool and gives the cutter its strength. The greater the wedge angle the stronger the cutter but it is more difficult to push into the work-piece. The Rake angle. This is ground to suit the material being cut and the greater the rake the easier it is to cut but the weaker the cutting tool. An angle of 20º is used for mild steel and an angle of 5º is used for cast iron.  The Clearance. If the flank of the cutting tool came into contact with the work the cutting edge could not take of a chip. The larger the clearance the weaker the cutting tool.

 

Wedge / Tool   Angles

wpeB.gif (3061 bytes)

  • The simplest form of a cutting tool has three main angles:-     Wedge, Rake and  Clearance.

  • The Wedge. This is often called the tool angle and is indicated by "B"

  • The Rake. This is indicated by "A" and the alows the chip to flow away.

  • The Clearance. This ensures that only the cutting edge touches the work-piece "C"

 

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Paddy Keays Engineering Teacher

Cresent College Comprehensive Limerick Ireland
Last updated 10th February 2004.

Comments to:-   email   paddykeays@eircom.net