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Cutter Flute Forms

Cutter Flute Forms
  Straight Cutter Types
Single Fluted Cutters
Straight, core box or engraving cutters are often ground with a single flute or cutting edge. With one larger flute produced, less body material is ground away than on other cutter forms. This produces a stronger cutter with better chip clearance characteristics, allowing faster feed rates to be maintained, but generally to the detriment of the finished cut edge.

Two Fluted Cutters
The most common form of router cutter is produced with two cutting edges ground symmetrically opposite each other. Two fluted cutters produce a far better finish, but should be used at a slower feed rate than single fluted ones to allow waste material to clear adequately. For Plunge cutting applications, a cutting edge is often ground on the bottom of the cutter. With tungsten carbide tipped cutters over 9.5mm in diameter, a third central tip normally of tungsten carbide is used to give a Plunge cutting facility.

Cutter Flute Forms
  Shaped Cutters
Shaped cutters are usually two fluted and are used for decorative moulding or jointing applications. By changing the depth or width of the cut, or by altering the table fence or side fence position, different profiles can be produced using the same cutter. With bearing guided versions, the fitting of an alternative larger diameter ball-bearing guide, will often produce a different shape. Typical standard profiles include bevel, radius, dovetail, roundingover, and rebate cutters.

Bearing Guided Cutters
Straight cutters are also available as self-guiding cutters, and are designed to follow the edge of the workpiece or a template fitted above or below it. Self guided cutters are used for trimming, moulding or rebating. To achieve this, a ball-bearing guide is fitted, or a solid pin is brazed into the nose of the cutter.
Cutter Flute Forms
  Ball-Bearing Guides
Ball-bearing guides can be fitted either to the cutter shank, above the cutting edges or on a spigot machined on the end or nose of the cutter. As the ball-bearing diameter predetermines the width of the cut from the board edge, by changing the ball-bearing guide for one of a different diameter, the width or depth of the cut can be altered.
Ball-bearing guided cutters have the advantage of reducing the setting-up time, as the maximum width of the cut (e.g. rebate) or depth of cut (e.g. grooved edge) is fixed by the ball-bearing diameter. The ball-bearing guide or pin is run against the edge of the work, with guide or template mounted above or below it.
This allows the cutter to follow a curved edge and avoids the need to use a side fence or parallel guide for straight edge work. The precision afforded by ball-bearing or pin guided cutters, is often critical when using interlocking or matched profile scribing cutters.
Ball-bearing guided cutters have an advantage over solid pin guided cutters, in that they produce less friction between the ball-bearing outer edge and the timber, reducing the risk of burning the edge of the workpiece. Ball-bearing guides are generally held in place by either a socket headed screw or hexagonal nut. In most cases a small washer is fitted, and should always be refitted when changing or refitting guide bearings.
Ballbearing guides for use on router cutters have shields fitted that reduce the amount of dust and dirt that can enter and clog the moving parts. Ball-bearing guides should be considered as consumable and non-serviceable items, and may need replacing during the life of the cutter. Never try to clean a ball-bearing with solvent, as this will dilute the grease lubricant. It is virtually impossible to replenish the grease, and any attempt to do so could prove dangerous or cause serious damage to the workpiece, as the ball-bearing is likely to collapse.
Cutter Flute Forms
  Pin Guided Cutters
Some basic shapes, such as ogees, core box, chamfer, rebating and trimming cutters are available with pin guides. These are used in similar applications as bearing guided types, yet are less versatile. They have the advantages that they can be used to shape or profile intricate shapes due to the smaller pin diameter. However, extra care is needed to prevent the edge of the workpiece or template burning due to the frictional heat.

Cutter Flute Forms
  Arbor Mounted Cutters
Arbor mounted cutters consist of single or multiple slotting cutters assembled on an arbor, using spacers, shims and ballbearing guides to adjust their proximity and depth of cut. This form of cutter offers a high degree of versatility, as the basic components can be mounted in different combinations, using the shims, washers and spacers to vary their spacing. In production operations, arbor mounted cutters can be used to save downtime and costs when changing or re-sharpening cutters and allow matched cutter sets to be fitted without affecting the machine settings.

The Trend Biscuit Jointer Set Ref. 342 consists of an arbor, 4mm groover and three bearings. This allows three different depths of groove to be jointed, for biscuit sizes 0, 10 and 20.
Another versatile tool using this technology is the profile scriber where the groover, bearing and profiler are rearranged to give perfect matching profile and scribe moulds. When in use the cutters should be staggered to each other at 90 degrees to reduce cutting impact. The bearing is the datum point of this tool and should be in contact with the timber at all times. This type of tooling should only be used with the router mounted in a fixed position.
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