Understanding Tool Geometry in CNC Routing
Tool Geometry
Routing tools come in many and varied geometries and grind styles. All this technology is aimed at producing the best cut in a wide range of materials. The choice of tool geometry is just as important as choosing the correct cut speed and RPM rate as it affects everything from edge finish to vibration during cut to chip removal.
Straight Flute
Use for wood and plastic operations. The straight flute design, in single or multiple cutting edges, produces a clean finish. The harder the material, the more cutting edges are recommended. The straight flute does not allow for the lifting of material out of the cut.
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Spiral Flute
Use for aluminium, wood and plastic operations. The up-spiral flute is especially good for chip removal. When cutting aluminium and plastic, re-melting of the chips is the primary source of poor cut quality.
Use single spiral flute tools for faster feed rates in softer materials. The single-flute cutter typically has lots of room for chips, but the single cutting edge limits either the feed rate or the hardness of the material to be cut. These types of cutters are especially recommended for plastics.
Use double or triple spiral flutes for a better finish in harder materials. Double-flute bits provide a smoother cutting action because the chip load is smaller than a single-flute cutter for a given feed. This allows harder materials to be handled.
Upcut spirals are the most popular type of spiral fluted tool. Use these for grooving or slotting, for upward chip evacuation and the best finish on the bottom side of the part. These bits allow for rapid cuts since the tool clears the chips away from the material. This type of tool is not recommended for softer materials because of the ragged finish that can result on the top surface. This type of geometry is used whenever the best finish is needed on the bottom side of a part.
Downcut spiral tools are best used for thinner materials which will be pushed down into the machine bed rather than being lifted with an upcut spiral. They are also best for leaving a good cut finish on the top surface of cut parts. Note that the cutting speeds usually have to be reduced because the chips are pushed back into the material. Chip extraction is generally less effective with this type of tool than it is with upcut spiral tools.
Rougher
Use for wood roughing or hogging operations. The rougher is designed to break up chips for fast, clean and efficient removal whilst reducing overall chip load. For extremely fast routing ofhardwoods and wood composites. Not ideal for composite materials or where a very fine edge finish is required.
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Compression Spiral
Compression spirals are used extensively for cutting double sided laminates. These tools can also be used on natural woods where edge finishing is a problem with standard spiral tools. This tool will leave a clean edge cut. They are available in single edge, double edge and three edge in coated and maximum wear compounds. Extremely popular with kitchen manufacturers and cabinetmakers. Capable of high feed rates for maximum production cycles.
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Chipbreaker Finisher
A combination of a chipbreaker and finisher tool. For additional balance at fast feed rates with a smooth finish. Very good in hardwoods, ply and wood composites.
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Finisher
Designed for perfect balance and smooth finish over a wide speed range. Primarily used on hardwoods and wood composites, they can also be used on plywood, MDF, Corian and acrylic.
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