Chapter Seven
Cutting tools
All machine tool operators need to have a basic knowledge of the cutting action of cutting tools.
Action of Cutting Tools
Cutting tools use a wedging action, the power used in cutting metal is expended in the form heat. When used to make heavy cuts a tool has a small ridge of metal directly over the cutting edge. This metal is much harder then the metal bring cut, coolants help absorb the heat from the cutting edge of the tool, in high-speed production work.
Materials
Here are some materials used for making cutting tools.
Carbon Tool Steel: Less expensive as other cutting tools, and can be used on some types of metal successfully.
High Speed Steel: The most popular cutting tool material, high-speed tools contain tungsten, chromium, vanadium and carbon.
Stellite: These bits can withstand higher cutting speeds then high-speed steel. Stellite is a non-magnetic alloy, harder than common steel (High-Speed) even if heated red hot by fiction, it will not lose its temper. Being harder than high-speed steel, Stellite is more brittle and is used for machining high steel cast iron and bronze.
Carbide: Tips of cutting tools are made of carbide for manufacturing operations where maximum cutting speeds are desired.
Tungsten Carbide: These cutting tools for machining cast iron, alloyed cast iron, bronze, copper, brass, Aluminum, Babbitt, and abrasive nonmetallic materials, hard rubbers and plastics. These tools are so hard they cannot be ground satisfactory on a regular grinding wheel.
Titanium Carbide: a combination of tungsten carbide and titanium carbide are interchangeable with tantalum carbide in its uses.
Shapes and Uses of Cutting Tools
Here are nine popular shapes of lathes cutter bits and their uses.
Left Hand turning tool-opposite of the right hand turning tool for turning in either direction, this tool is used in machine work from left to right.
Round-nose turning tool-used for reducing the diameter of a shaft in the center, this tool is for turning in either direction.
Right-hand turning tool-is the most common type of cutting tool for general lathe work used in machining work; this cutting tool travels from left to right.
Left-hand facing tool-opposite of the right hand tool, and is used for facing the left hand side of the work.
Threading tool- This tool is used to cut threads and the point is ground to a 60-degree angle.
Cutoff tool-is used where a regular turning tool cannot be.
Boring tool-is ground the same as a left hand turning tool; however, the front clearance angle is slightly greater. This is the heel of the tool will rub in the hole of the work.
Inside threading tool-is ground the same way as the screw-threading tool, except that the front clearance angle must be greater.
Terms Related to Cutting Tools
Base- Surface of the shank that bears against the support and takes the tangential pressure of the cut
Chip Breaker- this is to break chips into small pieces, can be an irregularity in the face of the tool or a separate piece attached to the tool or holder.
Cutting Edge- Portion of the face edge along which the chip is separated from the work
Face- Surface on which the chip slides as it is cut from the work
Flank- Surface or surface below and adjacent to the cutting edge
Flat- Straight portion of the cutting edge intended to produce a smooth machine surface.
Heel- Edge between the base and the flank immediately below the face
Neck- An extension of reduced sectional area of the shank.
Nose- A curved face edge
Shank- Portion of the tool back of the face that is supported in the tool post
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