Drilling Tools

This invention relates to drilling tools and is more particularly concerned with the provision of depth stop devices in such tools.

According to the invention there is provided a drilling tool having a depth stop device comprising a depth stop rod mounted on the body of the tool for guided sliding movement along the longitudinal axis thereof in directions parallel to the direction of drilling movement, and a lever mounted on the body of the tool for pivotal movement about an axis extending normally with respect to the longitudinal direction of the rod but offset to one side of the rod, said lever being resiliently biased into a rotational position about said axis on which position a detent edge of the lever engages the rod and movement of the rod relative to the body of the tool resulting from abutment of the rod with a workpiece operates in a sense to rotate the lever in the same direction as the biasing force thereon and to urge the detent edge into tighter engagement with the rod, and said lever being movable against the biasing force of the spring to disengage the detent edge from the rod.

While the frictional grip of the detent edge on the rod is adequate for very light tools, the surface of the rod engaged by the detent edge is preferably knurled to provide substantially a mechanical lock between the two components.

In preferred arrangements according to the invention, said detent edge engages the surface of the rod remote from said axis. In one preferred construction the rod extends through an aperture in the lever, part of the edge of the lever bounding the aperture constituting said detent edge.

In some circumstances according to the invention, the lever provides a second detent edge for engaging the opposite side of the rod from that engaged by the first detent, and means is provided for permitting limited relative movement of the lever and the rod in a direction generally lengthwise of the lever.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic plan view of a tool according to the invention,

FIG. 2 is a side view of the tool of FIG. 1,

FIGS. 3 and 4 are views along the section line A--A of FIG. 2 showing the depth stop device in its locked and unlocked conditions respectively,

FIG. 5 is a fragmentary view on the line B--B of FIG. 4,

FIG. 6 is a diagrammatic side view of the lever and rod of the arrangement of FIG. 1, and

FIGS. 7 and 8 are diagrammatic side views respectively showing two further embodiments of the invention.

Referring to FIGS. 1 to 6 of the drawing, the body of the drilling tool 10 is shown only in outline and carries a chuck in which a twist drill 11 is mounted in the usual manner. The depth stop device is mounted at one side of the body and the stop proper is constituted by a hexagonal section rod 12 which is mounted for sliding movement along the direction of the longitudinal axis thereof or forward and rearward parallel to the direction of drilling movement in guide apertures or bores formed in flanges 13 on the body which are spaced longitudinally along the direction of the rod and which are shaped to prevent the rod from rotating about its longitudinal axis. The top face 14 of the rod is knurled as shown in FIGS. 1 and 5. Between the flanges 13 the rod extends through an aperture in a lever 15 made for example from strong metal sheet. The lever is pivotally mounted on one end of a pivot boss 16 located on the body at a position below the rod. The pivot boss projects at substantially a right angle with respect to the longitudinal direction of the rod. About the pin the lever is flanged as shown at 17 in FIGS. 3 and 4 to provide a bearing, and intermediate its ends a 90.degree. twist is formed in the lever so that the free upper end part 18 of the lever extends in a plane generally normal to the axis of the rod. A torsion coil spring 19 is mounted on the pivot pin 16 and has two end parts 20, 21 of which part 20 abuts a stop surface 22 on the body and part 21 engages in a slot 23 in the upper end part 18 of the lever so as to urge the upper end of the lever rearward away from a workpiece engaged by the twist drill. In the illustrated embodiment, the slot 23 is shown opening to the bottom edge of the aperture in the lever. Referring now also to FIG. 6, the upper end part 18 of the lever is inclined rearward away from the workpiece so that the rearward edge of the periphery of the aperture in the lever forms a detent edge which can engage the serrations of the knurled surface 14 to form substantially a mechanical lock against sliding movement of the rod. A laterally projecting portion 18a of the upper end part of the lever is manually engageable by the operator to push the lever 15 forward and thus swing the detent edge forward and upward away from the rod to release the rod for adjustment. When the lever is released it locks again on the rod under the action of the spring 19. When the front end of the rod comes into abutment with the workpiece, any resulting rearward movement of the rod tends also to rotate the lever 15 rearward and hence pull the detent edge into tighter engagement with the serrations on the rod and therefore to resist the rearward movement of the rod.

The illustrated embodiment is advantageous in that all of the components are attached to the drill and there is no key or spanner to become mislaid or lost. It will be noted also that the flanges 13 protect the lever and spring against damage.

Referring now to FIG. 7, a modified embodiment is illustrated in which both the top and bottom faces of the rod 12 are engaged by respective peripheral edges of the aperture in lever 15. The distance between the two detent edges is greater than the distance between the complementary faces of the hexagonal rod and the guide apertures in the flanges 13 thus enabling the rod to move a limited amount in an up and down or transverse direction. When the lever is rotated by its spring, the two detent edges of the periphery of the aperture respectively engage the top and bottom surfaces of the rod and hold it against displacement in the longitudinal direction thereof. When the lever is rotated forward into a vertical position so as to disengage its detent edges, the rod moves upwards within its guide apertures to free the rod.

In the alternative arrangement illustrated in FIG. 8, the lever again has upper and lower detent edges for engaging opposite sides of the rod, but in this construction the rod is in a close sliding fit within its guide apertures in the flanges 13, and radial clearance is provided between the pivot boss 16 and the lever. This clearance enables the lever to float or move along its longitudinal axis to take up a position to which the rod is clamped between the two detent edges, and to release the rod when the lever is rotated or moved into its vertical position.