GB1400440A - Power tools - Google Patents

Abstract

1400440 Grinding E SANTILLI 6 June 1972 57333/71 Heading B3D [Also in Division B5] A power tool comprises an annular tool, e.g. a saw blade 36, Fig. 5, or a grinding wheel, a drive roller 30 mounted on a drive shaft for rotating the tool about its vertical axis 58, a tool support means 70 which acts as a pivot about which resistance forces R T between a workpiece 80 and the tool tend to swing the tool, and means acting via the roller 30 to counterbalance the forces R T . The rotational axis of the drive shaft is inclined to the plane of the tool, and an extension of the axis intersects the plane within a domain contained between a line Y, Fig. 1, starting at the midpoint of the tool-drive roller interface and extending in the plane of the tool in the direction of the radius through the mid-point, and a line X through the mid-point, at right angles to the line Y and on the working side thereof. The counterbalancing forces may be produced by adjusting the angle between the axis of the drive roller and the line Y, or by adjusting the pressure of the drive roller on the tool, or by moving the drive roller radially of the tool. As described, an annular saw includes a motor housing 21 connected to a blade housing 32. The motor housing includes a motor 26 which drives the roller 30, and the blade housing 32 includes guide rollers for restraining the blade against axial movement, and support rollers which restrain the blade against radial movement. The guide rollers engage the faces of the blade and the support rollers engage the inner rim or annular grooves in the blade, e.g. as is Fig. 11B. Some of the rollers maybe replaced by stationary self-lubricating pads, e.g. as in Fig. 8H, which also serve to wipe the saw blade. The tool may include a spacer plate located within the saw blade. Various methods are described for providing the counterbalancing means. In one embodiment the blade housing 32, Fig. 5, is pivoted to the motor housing for movement about an axis parallel to the axis 58 and passing through the mid-point of the roller-tool interface so that the angle between the drive axis and the line Y, Fig. 1, varies as the reaction forces vary. In another embodiment cam means is provided on the drive shaft of the roller 30 to urge it radially inwardly of the saw blade when increased resistance is encountered, thus increasing the pressure between the drive roller and the blade. In further embodiments, e.g. Fig. 11B, the blade housing 32 is pivotally mounted on the motor housing, e.g. at 96, and carries a roller 66 which is urged towards the drive roller 30 when the resistance increases. Quick release of the blade is also catered for in the Fig. 11B embodiment by pivoting the housing 32 by means of a lever 100. Other quick release means involving movement of the blade housing or the drive roller are also described, Figs. 11B, 12B, 13, 14, 15A, 15B, 15C, not shown.