Cutter types

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Cutters come in a variety of types to allow different forms of cuts. 

Cutter flute shape

The most common flute shapes are spiral and straight. The following table summarises the pros and cons of both types.

Cutter

Pros

Cons

Straight

  • No bias on top or bottom surface finish

  • May be sharpened

  • Can create poor finish on bottom surface of part

  • Neutral chip evacuation

  • High cutting forces cause more resonance in the job

Spiral

  • Better finish on bottom of parts

  • Better chip evacuation

  • Longer lasting

  • Slicing action means far lower cutting forces

  • Cannot be sharpened

Spiral cutter

Spiral cutters have the flutes ground on a spiral around the cutter body. There are different types of spiral cutters depending on what direction the flutes are cut into the cutter.

Upcut spiral flute

 


The spiral orientation of flutes is in a clockwise direction (shown in yellow). Chip evacuation is in an upward direction (shown in brown). Material shear is also in an upward direction, which may not create a desired edge finish on the top surface of the cut. 

Downcut spiral flute


The spiral orientation of flutes is in an anti-clockwise direction (shown in yellow). Chip evacuation is in a downward direction (shown in brown). Material shear is also in a downward direction, which will create a good edge finish on the top surface of the cut, but not at the bottom. 

Upcut and downcut spiral flute

This is a combination of upcut flutes at the tip of the cuter and downcut closer to the shank of the cutter.That’s a good choice for edge trimming plywood and hardwood.

Straight cutter

A straight cutter has a straight cutting edge. The quality of edge finish on top and bottom surface of the material is lower compared to the spiral cutters.

Straight cutters will not move chips away from the workpiece in the way that spiral cutters do. If using a straight cutter, ensure extraction is optimal.

Plunge features

Center cutting end mill 

A center cutting end mill has cutting edges on both the end face of the cutter and the sides. It can be used for plunge milling (down direction cutting).

Non-center cutting end mill

A non-center cutting end mill has cutting edges on the sides and the cutting edges at the end of the tool do not overlap, which makes it impossible to do a straight plunge. A tool like this can only be used  for side milling, if plunging is required it needs to ramp into the material.

Most common types of cutters

End mill cutter


This is the most common milling cutter and is used for most general milling applications. It produces a sharp edge at the bottom of pockets and slots. 

End mill cutters can be center cutting or non-center cutting.

Ball end mill cutter


This type produces a radius at the bottom of pockets and slots. Ball end mills are used for contour milling and pocketing applications.

Engraving cutter

Engraving cutters come with a tip angle (included angle) varying from 30° to 90° and are used for contour engraving.

Face mill

This type is a large diameter tool; it is used to cut a wide shallow path for facing operations.

Facing is used for machining a large flat area, typically the top of the part in preparation for other milling operations.

Cutter material

Cutters are normally made of HSS or carbide. The table below shows the advantages and disadvantages of the materials.

Cutter

Pros

Cons

HSS

  • Cheaper initial cost

  • Softer, so less durable (reduced tool life)

Carbide

  • Harder, so longer tool life

  • Faster cutting speeds

  • Higher initial cost

  • Brittle so need to be handled with care


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