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Basic knowledge of end mills (2) Elements that make up an end mill

Feb. 23 2022

This is the second article in our series on basic knowledge of end mills. In this article, we will discuss the elements that make up an end mill. 

 

Elements that make up an end mill

Diameter

Diameter of the outer circumference of the end mill.

In the case of a straight-flute end mill, the diameter remains the same from the tip to the cutting-edge limit on the shank side. In the case of tapered flutes, the tip diameter and taper angle are often specified.

 

Groove

 An indented portion that constitutes the rake face of the peripheral cutting edge.

 An indented portion that constitutes the rake face of the peripheral cutting edge.

 

Number of Flutes

The number of peripheral flutes in an end mill.

If the number of flutes is small, the groove depth can be deepened and a large chip pocket can be secured, resulting in high cutting efficiency, but the machined surface tends to be rough. As the number of cutting edges increases, the chip pocket becomes smaller and cutting efficiency decreases, but the amount of cutting per edge decreases, so the surface roughness of the machined surface tends to improve.

 

Helix

The spiral angle of the groove on the outer periphery of an end mill.

It promotes the evacuation of chips. It also has the effect of reducing cutting resistance and suppressing chatter. Generally, it is set at about 30°.

 

Rake face

An element of the end mill peripheral groove that constitutes the inner side (rake portion) of the peripheral flute.

It constitutes the outer cutting edge and plays an important role in chip pockets and the smooth discharge of chips.

 

Outer relief surface

An element that constitutes the outer cutting edge of the peripheral blade.

The available shapes are first relief surface and first and second relief surface. There are two types of relief, “concave” with a solid flank and “eccentric” with a round flank.

The concave shape is relatively easy to produce and re-sharpen, but the cutting edge tends to become brittle, and durability is inferior. Eccentrics are more costly to produce, but are more durable, and in recent years, eccentrics have been widely used.

 

Bottom Flute Clearance Surface

An element that constitutes the cutting edge of an end mill bottom flute.

The available shapes are first relief surface only and first and second relief surface When cutting in the vertical direction, the cutting edge of the bottom flank takes over the cutting. In ball end mills, it is important because almost all the cutting is done by the bottom flute.

 

Gash

An element that constitutes the rake side of the bottom flute.

Since the core thickness of an end mill is large, it is not possible to create a cutting edge in the center as it is. Therefore, a groove larger and deeper than the thinning of a drill is inserted to secure the cutting edge and discharge chips.

 

The above is an explanation of the main components of an end mill.

 

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