Tool geometry of a single point cutting tool is mentioned in the above image.
Let me explain each of these single point cutting tool angles one by one along with their significance.
#1) The Rake Angles
The rake angle is an angle which is at the upper side of the cutting tool.
There are two types of rake angles which combine to form an effective rake angle (also known as true rake angle or resistant rake angle).
These two rake angles are;
- Back rake angle and
- Side rake angle
Back rake angle
Back rake angle is the angle between the face of the tool and a line parallel to the base of the shank in the plane parallel to the side cutting edge. (See above image).
The chip formation from the workpiece depends on the back rake angle of the cutting tool.
Side rake angle
Side rake angle is the angle by which the face of the tool is inclined sideways. (See above image)
There are two major effects on the metal cutting process due to rake angle.
Rake angle affects the tool strength as well as it affects the cutting pressure.
Tool having a negative rake angle will withstand more loading as compared to a tool with positive rake angle.
Tool having a positive rake angle helps in reducing the cutting force by allowing the chips to flow easily across the rake surface.
There are few more functions of the rake angle.
- It allows the cop to flow in the convenient direction.
- It increases the tool life as it can reduce the cutting force required to shear the metal and this also helps in reducing the power consumption.
- It improves the surface finish of the workpiece.
Now one more thing I want to add for the rake angles. The rake angles are of two types.
- Positive rake angle
- Negative rake angle
Positive rake angle
The above image shows you the positive rake angle in a single point cutting tool.
The positive rake angles reduce compression forces as well as friction between the tool and workpiece.
This results in thinner, cooler and less deformed chips.
The main disadvantage of increasing the rake angle is that, it reduces the strength of the tool section and also reduces the heat conduction capacity.
Positive rake angles are more beneficial for cutting tough alloyed metals.
Negative rake angle
Negative rake angles improve the strength of the cutting edge and they are good for better heat conductivity.
Generally, negative of zero rake angle is made on carbide tools as well as ceramic cutting tools.
These are brittle materials but they have the ability to withstand high temperature and hence they can be used for high speed and continuous machining processes.
Negative rakes are generally prefered for the tools which do not have good toughness.
As a result, negative rake causes high compression force and friction which results in highly deformed hot chips.
Few important things about negative rake angle
- Material like cast iron which is hard for machining, can be machined with cutting tools having negative rake angles.
- Cemented carbide tools are applicable for the high speed machining operations. At such high operating speed, the rake angles have less effect on the cutting pressure. For such situations, the rake angles are kept zero or negative to increase the tool strength.
- In rough turning operations, more depth of cut is required for the metal removal process. In such cases, the cutting tool needs to withstand high cutting pressure. Hence, the rake angle is reduced to increase the strength of the tool.
- Some old and worn-out machines cannot handle high cutting pressure. In such cases, the cutting tool having more rake angle is preferred which can handle the high cutting pressure.
#2) Relief Angles
Relief angles are necessary to provide on the cutting tool to avoid the interference of machined surface with the cutting tool.
By providing the relief angles on the cutting tool, the life of tool increases as well as it eliminates tool breakage.
Also one important thing is that if the relief angles are very large, then the tool may break on high cutting pressure.
And if the relief angle is very small, then the tool will rub against the machined surface which results in more heat generation.
It is very essential to have a small relief angle for machining hard and strong materials.
Small angles are prefered for heavy feeds whereas large angles are prefered for finishing cuts.
There are basically two relief angles on the single point cutting tool. They are;
- Side relief angle and
- End relief angle
Side relief angle
The main purpose of giving side relief angle is to prevent the side flank of the tool from rubbing against the workpiece when longitudinal feed is given.
End relief angle
The main purpose of giving and relief angle is to prevent the front flank of the tool from rubbing against the workpiece.
The end relief angle (or front clearance angle) should be increased for larger diameter workpiece.
#3) Side Cutting Edge Angle
The side cutting edge angle is shown in the very first image of this article.
Side cutting edge angle is provided for the following benefits;
- It increases tool life because by providing the side cutting edge angle, the cutting force is distributed on a wider surface.
- Heat dissipation is faster as it has a wider cutting edge.
- The side cutting edge angle has generally no effect on the value of cutting force or power consumption.
#4) End Cutting Edge Angle
The end cutting edge angle is shown in the very first image in the beginning of this article.
The main function of the end cutting edge angle is to avoid the rubbing of trailing front end of the cutting tool with the surface of the workpiece.
Larger end cutting edge angle unnecessarily weakens the tool, hence this angle is kept between 8 to 15 degrees.
#5) Nose Radius
The nose of the cutting tool is kept slightly rounded in most of the single point cutting tools.
The nose radius has the following importance.
- Greater nose radius helps in clearing the feed marks on the workpiece and this gives the better surface finish.
- Finishing tools generally have more nose radius as compared to the rough turning tools.
- By providing the nose radius, the strength of the cutting edge increases.
- Heat accumulation is also less if the nose radius is more.