There are different ways to classify end mills.
- Click below for explanations reffering
to the classification of end mills by geometry.
The number of flutes
The number of flutes is generally two, three, four and six. The difference in the number of flutes leads to the difference in the area of chip pockets (flutes).
Chip pockets are used to dispose of the chips developed when machining. The proportion of the area of the flutes against 100 percent of the cross-section of a rotating end mill is as shown in the picture.
Generally as the number of flutes increases then the narrower or smaller the flute ratio becomes. With an increase in the number of flutes the ratio of the cutting edge area increases and as such tool rigidity is increased. Features and applications depend on the number of flutes (see table below).
Comparison of sectional area of chip pocket.
Characteristics and applications of different-number-of-flute end mills.
Effective chip disposal. Horizontal feed milling possible.
Low rigidity.
Various cutting modes including slotting, shoulder milling and drilling.
Effective chip disposal. Horizontal feed milling possible.
Diameter is not measured easily.
Slotting, shoulder milling.
Heavy cutting, finishing.
High rigidity.
Chip disposal is poor.
Shallow slotting, shoulder milling Finishing.
High rigidity. Superior cutting edge durability.
Chip disposal is poor.
Machining hardened steels. Shallow slotting, shoulder milling.
Cutting edge length
When an end mill is located into a chuck it will suffer from deflection due to cutting resistance during machining as shown in the figure. The amount of deflection is proportional to cutting resistance, and is proportional to the cube of a length from the end of a chuck to the end of an end mill, or an overhang length.
To reduce the amount of deflection and produce vertical machined surfaces, end mills with as short overhang length as possible should be used. Therefore, flute lengths of end mills are divided into the following.
a. Extra short
b. Short
c. Standard
d. Semi long
e. Long
f. Extra long
Deflection of end mills
Helix angle
The hand of the helix of end mill is generally (see image) and will be used by rotating clockwise (right-handed) viewed from the shank side. Cutting tools that are used by rotating right-handed are called right hand end mills. Cutting tools that are used by rotating anticlockwise (left-handed) are called left hand end mills. The Image below shows a right-handed helical tooth.
Left-handed helical
tooth 30° to left.
Usually, there is no left-handed helix.
Right-handed helical
tooth 30° to right.
Rotate right-handed viewed from the shank side.
The helix angle of end mills is usually 30°. A small helix angle gives less sharpness as the helix angle becomes larger the sharpness of the end mill improves. However as the helix angle increases the axial force increases and can have a tendency to pull the end mill towards the work. The table shows features and applications of different-helix-angle end mills.
No waviness of the machined surface but less sharp. Used after sharpening mainly into a formed or tapered flute.
In case of high-speed steel end mills, used to reduce machined surface waviness. End mills with low helical flutes include ones for machining a key way*.
Used for general-purpose end mills due to good balance of machining accuracy and sharpness.
Sharp. In case of high-speed steel end mills, big machined surface waviness.
Effective for the machining of difficult-to-machine materials, such as stainless steel, and hardened steels.
Helix angle
Peripheral cutting edge
The Table shows various geometries and features of a number of end mills.
Shape of peripheral cutting edge
The most general-purpose type of end mill. Used for roughing, medium finishing and finishing of slotting, side milling and shoulder milling. Wide variety.
Used for machining a slope part and a centering location part. Used for applying taper angles after cutting with an ordinary flute.
Has a wavelike edge form and breaks chips into short lengths. Low cutting resistance. Effective for roughing. Not ideal for finishing due to rough surface finish. Requires grinding of the rake face.
Although the drawing to the left shows an end mill for producing corner radii on components, the formed edge type end mills are designed to suit the geometry required. These tools are mostly made to order.
For general use. Used for slot milling and side milling. Can not be used for horizontal feed machining. High regrinding accuracy because of both centre holes being held during grinding.
For general use. Used for slotting and side milling.
Can be used for horizontal feed machining. The fewer cutting edges, the better horizontal feed machining performance.Regrinding with one end held.
An end mill that has a radial cutting edge. Used for curved surface machining.
Used for corner radius milling and machining a flat part.
End cutting edge
The table shows various types of end cutting edges of end mills. Among them the centre cut edge type that include two types. One type has long and short edges (A, C) and the other type has edges touching at the centre (B). Both can be used for horizontal feed machining.
Shank
The table shows various geometries, types, and features of shanks of a variety of end mills. Among them, the flattened straight shank and the combination lock shank are used mainly for indexable end mills.
Geometry of shank
A long shank is designed for deep slotting. Can have the tool overhang appropriate to machining depth.
With a flat to fasten an end mill with a screw to prevent the end mill from coming off.
Used in case an end mill comes off even with a flatted straight shank. Used for a large-diameter end mill designed for deep slotting.
Long neck end mill.
Deep slotting.
Taper neck ball nose end mill.
Deep slotting of mould darft wall.
Used for deep slotting with a small-diameter end mill. Also suitable for boring.
Higher efficiency in deep slotting a mould draft wall.
Neck
The table shows various geometries, types, and features of necks of a variety of end mills.
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