TYPES OF BURRS
TYPES OF BURRS |
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The two basic types of burrs are Spiral and Diamond Burrs.
Fig.7 Spiral Burr
The Spiral Burr has teeth running at an angle to the axis of the burr. This is called the lead angle. The lead angle may vary between 5º and 75º. Although commonly referred to as lead angle, the teeth of the Spiral Burr are not in the form of a thread and do not produce a thread type pattern on the pulpstone.
Spiral Burrs, when applied to the pulpstone produce a series of diagonal impressions on the face of the stone. The angle of these grooves in relation to the axis of the stone corresponds to the angle of the "lead" or angle from the axis of the burr and the pulpstone. Since these grooves are not parallel with the grain of the wood, they remove the fiber from the wood with a shearing action.
The nearer the spiral lead angle is to 0º (short lead) the longer are the fibers produced. Conversely, the greater the lead angle the shorter the fibers will be. Short lead burrs produce more pulp than long lead burrs, but usually the quality of the pulp is not as good.
Spiral Burrs can be supplied in varieties of pitches and lead angles. The most widely used lead angles are 24º, 28º, and 45º. The great majority of stones today are sharpened with the Spiral Burr.
 Sketch 1 |
 Sketch 2 |
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| Fig.8 Measuring Pitch and Lead | ||
For the purpose of illustrating the terms "pitch" and "lead" we are showing two Sketches (Fig 8.) which have in theory been produced by rolling a Spiral Burr on a piece of paper as indicated by the arrows. The sketches show the pattern that would be produced on the surface of a pulpstone.
Sketch No. 1 shows how the pitch is obtained by measuring off one inch (25.4mm) as indicated. The number of impressions included within this inch is the pitch of the burr. In Sketch No. 2 we see that drawing a perpendicular from one end of the burr tooth to the opposite edge of the burr has produced a right angle. The angle lying between the perpendicular and the burr tooth is the angle of lead. An older method of stating lead was in inches. The following table converts inches of lead to angle of lead in degrees.
| Inch(es) of Lead | Angle of Lead | Inch(es) of Lead | Angle of Lead | |
| Table 1 Lead Angle Conversion Table | ||||
| Fluted Burr | 0 | 2¼" | 38 | |
| ¼" | 5 | 2½" | 42 | |
| ½" | 10 | 2¾" | 44 | |
| ¾" | 15 | 3" | 47 | |
| 1" | 20 | 4" | 55 | |
| 1¼" | 24 | 6" | 65 | |
| 1½" | 28 | 8" | 70 | |
| 1¾" | 32 | 10" | 74 | |
| 2" | 35 | |||
Fig.9 Diamond Burr
The Diamond Burr is made by cutting grooves or flutes in the steel at right angles to each other. This produces a pyramid or diamond shaped tooth. Diamond Burrs are made in sizes 6, 8, 10, 12, 14, 16, 18, and 24. These numbers denote the number of teeth per inch (25.4mm).
The Diamond Burr is used for truing the pulpstone and the removal of stone patterns. Very fine Diamond Burrs are used for stone cleaning and land conditioning. On rare occasion this burr is used as the primary sharpening burr.
