End Hook for Power Return Tape Measure

The present invention is directed to tape measures. More particularly, the invention is directed to an end hook for a tape measure having a power return mechanism.

Power return tape measures commonly experience breaking of the free end of the measuring tape at the location where an end hook is fastened. Typically, an extended tape is returned to the housing by releasing a locking mechanism and allowing the return mechanism to retract the tape into the housing. The returning movement of the tape is stopped when the end hook strikes the housing. The collision of the end hook with the housing transmits a shock from the end hook through the fastening rivets to the measuring tape. After repeated collisions the tape material (usually steel) fails at the mounting rivets and the tape breaks.

The present invention provides a solution to the problem of failure at the end of the tape by better distribution of the collision shock to the tape.

The present invention also provides an end hook in which the fastening of the end hook to the tape is designed to minimized stresses introduced in the tape when fastening the end hook to the tape.

According to the invention, an end hook for a power return tape measure comprises a shank portion arcuately shaped about a longitudinal axis and a catch portion extending at an angle from the shank portion. The end hook and tape are formed with holes in a matching pattern so that the end hook is positionable on the tape with the respective holes aligned in pairs to accept a fastener.

According to one aspect of the invention, all of the holes on the shank of the end hook are spaced laterally from the longitudinal axis of the end hook. The holes in the measuring tape are similarly spaced from a longitudinal axis of the tape. The holes are positioned on a portion of the end hook and tape where the radius of curvature is relative large, that is, a portion of the tape which is relatively flat compared to its curvature at the longitudinal axis. Positioning the fastening holes away from the longitudinal axis minimizes mechanical stress introduced into the measuring tape by the fastener.

In a preferred embodiment, four holes in a rectangular pattern are provided on the end hook and a corresponding four holes in an identical pattern are provided on the tape. The holes are preferably arranged in two parallel, longitudinally spaced rows which spreads the collision force over a large area of the tape.

According to another aspect of the invention, the holes in the shank are slot shaped, being longer in the longitudinal direction than in the lateral direction.

According to yet another aspect of the invention, a longitudinal spacing of the holes in the shank is greater than a longitudinal spacing of the holes in the measuring tape. This helps control the distribution of shock forces from the end hook collision to be transmitted first to the rivets in the holes nearest the catch of the end hook. The tape stretches slightly and the rivets in the holes farther away from the catch then take up the force. Control of the distribution of the force in this manner has been found to greatly extend the service life of the measuring tape.

Another aspect of the invention is in the shape of the bend between the shank and the catch portion of the end hook. The bend is J-shaped, that is, from the shank the hook first bends in a first direction to form a ridge of small radius, then bends in the opposite direction to form the catch. The ridge at the end of the shank defines a small recess between the end of the shank and the main part of the catch. The recess accommodates the end edge of the measuring tape so that when the end hook is moved in the direction of the tape, no bending or distortion of the end edge is caused by the shank. This is advantageous in inside dimension measurements made by abutting the end of the hook against an object.

The invention will become better understood through the following description in conjunction with the appended drawings, in which:

FIG. 1 is a top view of an end hook in accordance with the invention;

FIG. 2 is an end view of the end hook of FIG. 1;

FIG. 3 is a section view of the end hook taken along the line 3--3 in FIG. 2; and

FIG. 4 is a top view of the end hook fastened to a free end of a measuring tape.

The invention is described in conjunction with a power return tape measure, for which the end hook according to the invention is particularly advantageous. The end hook may also be used for other types of tape measures, and the following description is meant to be illustrative rather than limiting.

An end hook 10 according the invention is shown in top view in FIG. 1 and an end view in FIG. 2. The end hook 10 is formed from a rigid material, for example, steel, and is shaped to have a shank 20 and a catch 30. The end hook 10 has a bend between the shank 20 and the catch 30 so that the catch 30 is at an angle to the shank 20. In the embodiment shown, the catch 30 is perpendicular to the shank 20.

The bend includes a ridge 40 between the shank 20 and the catch 30. As seen in FIG. 3, the ridge 40 is formed by a first bend from the plane of the shank 20 followed by a second bend in the opposite direction, thus providing a small recess 44 between the end of the shank 20 and the catch 30. When the end hook 10 is fastened to a measuring tape, the recess 44 provides a space to accommodate the end edge of the tape, which prevents buckling or bending at the end of the tape during use.

Referring again to FIG. 1, a longitudinal axis 12 extends the length of the shank 20. As seen in FIG. 2, the shank 20 is curved about the longitudinal axis 12 and is convex in the direction of the catch 30. Measuring tapes are also similarly curved to provide stiffness in the tape when the tape is extended from the housing.

The catch 30 is used to hook onto a reference edge of a thing being measured, and the catch may be provided with a nailing hole (not shown) or burrs on the inner surface to help hold to a reference edge. The catch 30 also prevents the free end of the tape from retracting into the housing.

The shank 20 is provided with a plurality of fastening holes 24 for fastening the end hook to a measuring tape (shown in FIG. 4). As mentioned, a common problem in power return measuring tapes is breakage of the end of the tape where the end hook is fastened. The user typically releases a locking mechanism holding the tape in the extended position, which frees the power return spring to re-coil the tape. The retracting movement is stopped by the catch of the end hook striking the housing. The shock of the collision is transmitted from the end hook through the mounting rivets to the measuring tape. After repeated collisions, cracks appear in the tape, which eventually lead to the end of the tape breaking off.

Conventional fastening systems for end hooks typically include two or more rivet holes disposed along the longitudinal axis. Attempted solutions in the past have included adding a third rivet on the longitudinal axis, adding reinforcing material to the measuring tape, and positioning shock absorbing bumpers on the housing.

According to the invention, the fastening holes 24 are positioned laterally spaced from the longitudinal axis 12 of the shank 20. At the longitudinal axis the tape has its greatest curvature and becomes flatter toward the lateral edges. It is believed that one source of the common breakage problem is that the force of fastening a rivet on the longitudinal axis causes a local flattening of the curvature in the measuring tape. The local flattening is believed to cause small cracks in the material that become starting points for larger cracks. The region of the measuring tape laterally away from the longitudinal axis, which is relatively flat, is subject to much less deformation in fastening.

According to a preferred embodiment of the invention, as illustrated in FIG. 1, four fastening holes 24 are provided and are positioned symmetrically with two holes on each side of the longitudinal axis 12. As seen, the holes 24 form a first row 26 of two holes adjacent the catch 30 and a second row 28 of two holes longitudinally spaced from the first row.

FIG. 4 illustrates an end hook 10 in accordance with the invention in position for fastening to the free end of a measuring tape 50. The measuring tape 50 is provided with an equal a plurality of holes 54 positioned in an identical pattern as in the end hook 10. The end hook shank 20 is positioned on the free end of the tape 50 with the longitudinal axis 12 of the end hook aligned with a longitudinal axis of the measuring tape 50. The holes 24 in the shank 20 and the holes 54 in the measuring tape form aligned pairs for inserting a fastener therethrough.

The four hole pattern illustrated in FIG. 1 and FIG. 4 provides an advantageous distribution of the shock force both laterally to the relatively flat portions of the measuring tape 50 and longitudinally over a portion of the length of the tape. This configuration is believed to allow the tape to better absorb energy and significantly reduces the rate of breakage, as testing, further described below, has indicated.

The holes 24 in the shank 20 are elliptically or slot shaped, that is, longer in the longitudinal direction than in the lateral direction. This permits sliding of the end hook 10 relative to the end of the measuring tape 50 to account for the thickness of the catch 30 for accurate measurements whether the end hook 10 is hooked over an edge of an object being measured or abutted against an object for an inside dimension measurement.

Fasteners, typically rivets or similar suitable fasteners, are not illustrated in FIG. 4 so that relationship of the holes 24 in the shank 20 and the holes 54 in the measuring tape 50 can be seen. According to another aspect of the invention, the longitudinal spacing of the holes 24 in the shank 20 is greater than a longitudinal spacing of holes 54 in a measuring tape 50. This differential spacing helps to distribute the collision force between the first 26 and second 28 rows of holes for improved durability of the measuring tape 50.

This may be better understood by considering what occurs when the measuring tap 50 is retracted into the housing. As previously described, the power return spring will recoil the measuring tape, retracting the tape into the housing until the end hook 1 collides with the casing. At the time the collision occurs, the measuring tape 50 is acting under a force in the direction of the arrow 60. The collision of the end hook 10 on the casing produces a force in the direction of the arrow 62, thus placing the measuring tape 50 under a sudden tension.

The differential longitudinal spacing of the shank holes 24 and tape holes 54 results in the collision force being transmitted first through the first row 28 of holes to the rivets and measuring tape 50, slightly before the force is transmitted through the second row 28 of holes. Analysis by the inventor has shown that in conventional end hooks and tapes, the breakage more often occurs at the hole farthest from the catch portion of the end hook. The end hook according to the present invention puts the load first on the forwardmost portion of the tape, and then allows the farthest holes and rivets to take up force. According to a preferred embodiment, the longitudinal spacing of the fastening holes 24 of the shank 20 is 0.005 to 0.01 inches greater than the longitudinal spacing of the measuring tape holes. Spacing differentials less than 0.005 are also believed to be effective. The differential spacing may be created, for example, by the shank holes 24 having a greater longitudinal center-to-center difference than the holes in the measuring tape. Alternatively, the holes in the second row 28, that is, the holes farthest from the catch 30, may be slightly longer than the holes in the first row 26. It is thought that in conventional measuring tapes (in which the hole spacing on the end hook and the tape is identical), the dynamics of the collision result in most of the collision force being absorbed by the holes farthest from the catch, rather than more equally distributed.

Testing by the inventor has shown that the operational life of the measuring tape is greatly improved by the end hook 10 according to the invention. In cyclic endurance testing, a tape with an end hook according to the invention survived more than 21/2 times as many collisions as a conventional end hook. A conventional end hook with longitudinally positioned mounting holes was found to survive in best cases about 3500 cycles before failure. By contrast, end hooks according to the invention repeated 10,000 to 11,000 cycles before failure.

The invention has been described in terms of preferred embodiments, however, it will be apparent to those skilled in the art that various changes, modifications, and the substitution of equivalent structure can be made without departing from the spirit and scope of the invention as defined in the following claims.