Patents Part 18 200309

The first requisite is that the clamping piece F should be left at liberty to take a secure bearing upon the wire. If the latter were perfectly straight and cylindrical, and the under surface of F perfectly flat, this bearing would take effect along the line GH, which is the line of contingence of the said plane and cylinder.

But in practice a rounded or twisted surface would defeat this object, and therefore the middle of the bearing surface of the clamp is filed away as shown in the front view, fig. 1006, so as to insure a pinch at or near each extremity of the line GH. (For the same reasons the notch in the stem piece should be filed away in the middle as also shown).

The bearing as the other extremity M of the clamp, is upon a round headed, short, hard steel pin, driven tight into a hole in the item piece. The head of this is received freely into a notch filed lengthwise in the tail of the clamp, as shown by the dotted lines. This allows the clamp to settle itself freely upon this bearing point, and at the asms time prevents it from turning round and shift ing its proper position upon the stem.

Thus the pressure of the screw K is distributed upon the three points G,H and M; and, by the well-known principles of statics, if N be the bisection of GH, and if the center of K lie in the straight line joining N and M, then will the pressure of the screw be equally divided upon G and H, whatever be the angle GNM. Fur if MK be equal to twice NK, the pressure of the screw upon all three points will be equal. However, it is better to throw M as far from the screw as possible, for thus loss pressure is exerted upon M, and therefore more upon G and H.

Finally to ensure the free transmission of the pressure of the screw to the clamp without jamming or wedging, a spherical washer L is interposed between the head of the screw and the clamp, and is received into a corresponding cavity turned in the clamp. If this be thought too expensive an arrangement, the lower part of the head of the screw may be made spherical, and received into a conical or countersunk cavity. Care must be taken to make the hole in the center of the clamp F, through which the screw passes, considerably larger than the diameter of the screw; else all these arrangements to enable the clamp to settle itself freely upon its bearing points may be defeated, by its being driven laterally against the screw. A short wire spring, coiled loosely round the screw between the clamp and the stem piece and touching the clamping piece between K and N, serves to press this piece outwards against the spherical washer and also keeps it in contact with M, and thus prevents it from hanging loosely when the wire is withdrawn.

(A new Tool-holder for the Slide rat).

In the ordinary tool-holder or contrivance by which the tool is secured to the table of the slide rest, no provision is made for placing the tool in various angular positions. The stem must lie parallel, or very nearly so, with one side or the other of the table, or in other words, we have but the choice of two directions for its stem. If it be desired to present the point of a tool in an oblique direction, it can only be effected by bending the tool itself. I am aware that contrivances have been proposed to enable the tool to be fixed angularly, as for example, "Mr. Pars-son's Improved Box for a slide rest," (described in the Society of Arts' Traiuaciions, Vol xlviil, page 240), which is, I believe, but little used, and in principle of construction is entirely different from mine

The contrivance I am about to describe I conducted in the spring of 1842, and have had in use ever since, and it was also immediately adopted by Mr. Holtsspffel, by whom it has, I believe, been found perfectly effective.* It enables the tool to be fixed at any required angular position upon the table of the slide rest, and is besides capable of being entirely removed from the table, so as to leave it free for the reception of other contrivances, as for drilling, cutting wheels, etc The tool-holder is shown in plan in fig. 1008, and in elevation (partly sectional) in fig. 1007.

In this tool-holder the tool is secured in its position by the action of a single nut A, which is tapped to a strong screw pillar BC. This screw has a round shoulder below which bears upon the surface of the table; beneath this shoulder is a short portion of screw C, which is tapped into a hole in the table. The screw pillar can therefore be removed or replaced by means of a key applied to flat faces filed upon the shoulder. The pressure of the nut A is transmitted to the upper surface of a triangular clamping piece DEF fig. 1008, through the interposed spherical washer G, which works freely in a corresponding cavity in the triangular clamp, as shown in the section fig. 1007.

* Nearly all the sliding rests in the author's manufactory have been fitted with Mr. Willis's apparatus for grasping the tools, and which answers so completely as to be always adopted in sliding rests for metal turning now made therein.

Two short rounded studs of hard steel D E, are driven into the lower side of the triangle, and rest upon the upper surface of the stem of the tool. At F a screw is tipped stiffly into the triangle, and its lower end being rounded like those of the studs D and E, it follows that when the nut A is brought into action, its pressure upon the triangle is resolved upon the three bearing points below, namely upon the two, D E, which press upon the tool, and clamp it to the surface of the table, and upon the third at F which presses upon the table through the intermediate piece H, which is principally interposed to save the table from bruises.

If the nut be loosened the tool and triangle are set at liberty, and the latter may be placed in any required angular position, when a turn of the nut at once fixes it completely. But as it is necessary that the tool should be under the studs D E, and therefore always at the same distance from the center of the screw, the intermediate piece H is contrived also to answer the purpose of guiding the stem of the tool readily to this distance.