Fig. 1007

Patents Part 19 200310

The outline of this piece is exactly the same as that of the triangle under which it lies, with the exception of the side which is parallel to the tool. The side is made at such a distance from the center of the screw that when the tool rests against it, it is set in the proper position to receive the pressure of the studs D E, of the triangular claw p. The dotted lino k l fig. 1008, is the boundary of the lower piece, and at the opposite extremity of this piece a thick lump is formed in which a notch or groove is filed in a direction pointing to the center of the screw pillar. This groove receives the end of the screw F as already explained. The form and thickness of the lump and the position of the groove are shown by the dotted lines in the figures.

The triangle and washer are drawn in section in the upper figure, to explain the adjustment of the washer G. As the upper surface of this washer is always horizontal, the hole need be no larger than is sufficient to pass freely up and down the screw pillar. But the case is different with the triangle D E F, for as that is required to accommodate itself to irregular thicknesses of the tool, that may throw it out of the horizontal position, the hole through which the screw pillar passes, should be large and slightly conical as shown in the section. In fixing the position of the screw pillar, upon the table of the slide rest, it should be placed at such a distance from the two edges that the bearing points, D E F of the triangle, may not bang over the edges in any position, but that the tool may be always clamped within the limits of the table; the dotted circle in the plan explains this sufficiently.

A circular hole in the middle of the piece H fits loosely the shoulder of the screw pillar, and as the end of the screw F is received freely in the groove of the intermediate piece, which latter is thereby kept in its proper place below the triangle, it follows that the whole combination of tool, triangle, and intermediate piece, may bo swung round the central pillar without escaping from their proper relative positions.

The screw F is introduced to allow of adjustment for tools of greatly differing thickness. But if it be necessary to put thin wedges under either end of the stem of the tool in order to raise or depress its point, the spherical washer allows of this by transmitting freely and centrically the pressure of the nut notwithstanding that the upper surface of the triangle becomes inclined from the horizontal position. It must be also observed that the tool may be placed either to the right or left of the screw pillar at pleasure, and a spiral spring may be introduced below the triangle, to prevent it from falling down when the tool is withdrawn.

The triangle should be made of such a size that the distance between its bearing pins D E, may be the same as that which would be given to the binding screws of on ordinary tool-holder.

Note AW, to follow the first paragraph 542. (Mr. Franklin's Expanding Center Bits.)

This modification of the center bit, fig. 457, page 541, enables a series of three tools, to bore all holes intermediate between half an inch and two inches in diameter, and that with very little interference in the general principle of the tool.

In figure 1009 the two parts of the instrument are separated beyond the distance at which they are used, in order to show the construction, and from which view it will be seen that the part a, of the expanding bit, which is squared at the end to fit the carpenter's brace, is extended at the other end, to form the central pin d. by which the tool is guided. The moveable part carries the scoring cutter or nicker e, and this piece admits of adjustment of diameter, it being attached to the main stem by the rivet ft, end fastened thereto by the bindiug screw c, that passes through the mortise in the moveable piece; this latter part is formed to constitute the lateral cutter f, by which the shavings are as it were swept out of the hole that is being made.

When the center bit is contracted to serve for its smallest diameter as in fig. 1010, the radii of the nicker and cutter are just alike, but it is found that the radius of the nicker may be increased above one-fourth as in the dotted position, and that still the cutter acts fairly, as the shavings become readily disengaged. These expanding bits are not intended to supersede the ordinary center bits of fixed sizes, but to serve for occasional works; and they are extremely well suited to the wants of amateurs.

Patents Part 19 200311

Note AX, to follow the paragraph, page 544, commencing "another Screw Auger.'.

(The American Screw Aug<r.)

The American screw auger, fig. 466, page 543, was patented by Mr. Wm. Ash, of Sheffield, and is described in the "Practical Mechanic and Engineers' Magazine," Glasgow, 1842, Vol. 1, page 108.

This description speaks of a different modification of the screw auger, from that described in the text, and in which a piece called a guide is employed instead of the worm usually soldered to the shaft. The guide consists of two thin rings, united concentrically by two fins situated on a diametrical line, leaving two large semi-annular spaces between them. The outer ring is made as a short conical screw, the inner embraces the central stem of the auger, upon which it fits loosely behind the cutter.

The auger first bores a shallow hole, into which the loose guide ring is screwed to serve for the guidance of the instrument, by the central ring or thimble which fits the auger shaft, and the shavings have to escape through the annular spaces betwixt the two rings. This part of the contrivance appears, however, to bo far less practical than that described in the text.

Mr. Phineas Cooke was rewarded by the Society of Arts in 1771 for the invention of the screw auger fig. 463, page 543, but the difficulty and expense attending its first construction, appear long to have withheld it from general use. - See also Smith's Panorama of Science, Vol. 1, p. 113.