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Cutter Geometry

Cutter Geometry
  Clearance angles and radial relief
Trend cutters are designed to ensure adequate chip clearance and to limit friction, therefore preventing overheating along the cutting edges and workpiece face. Care must be taken to stay within the chip clearance characteristics of a specific cutter while machining, by working at a suitable feed speed and not exceeding the recommended cutting depth and cutter speed in relation to its size and the application.

Rake angle and cutting angle
This is calculated to ensure the correct cutting action of the cutting tip to suit the application. A low rake angle produces a scraping action. A higher rake angle produces a deeper cutting or planing action.

Gullet or flute size
This dictates the maximum amount of material each cutting edge is capable of removing per revolution.

Chip limitation
To comply with generally accepted safety regulations (BG Holz), safety router cutters above 16mm diameter have a chip limitation of 1.1mm. This does not affect the efficiency of the cutter, and reduces the likelihood of kickback. It ensures that if personal contact is accidentally made, the degree of injury possible is minimised.

Centre tips
Centre tips ground onto the end of cutters are designed for Plunge cutting and drilling applications. The tip must again have its own clearance and cutting angles to ensure that the material is machined and not ground or burnt away. Some cutters, including straight flute profiles that do not have centre tips, are designed for profiling or trimming applications only. They will in most cases have clearance for lateral cutting but not for Plunge cutting.

The shank
The shank is machined to precise tolerances to ensure correct mating and grip within the router collet and to turn concentrically to the router axis. The most common sizes in the UK are 6.35mm (1/4), 9.5mm (3/8) and 12.7mm (1/2) diameters. Larger sizes are available for high volume production equipment and applications. Metric, 8mm diameter shanks have been introduced in the UK in recent years to cater for smaller router users needing to use larger types of cutters safely. Generally shanks of 8mm and 12mm diameter are manufactured for the European market. The correct geometry of a cutter is critical in order for it to perform correctly at its high optimum cutting speed. The angles such as rake, cutting and clearance are carefully designed to suit each type of cutter. This varies according to its size, the cutter material or to suit its specific application.
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