This invention relates to level measuring devices which shall provide consistently accurate service over an extended useful life. The invention also relates to methods of producing such levels by affixing resilient end plates to level frames.
Of paramount importance in the level trade, and particularly levels produced for carpenters, is the need for the provision of level devices which are both durable and consistently accurate and which can be sold at competitive prices. The level of the invention fulfills each of these trade needs.
As a result of both the high manufacturing cost involved in the production of metal end fixtures for level instruments and field problems experienced with inaccuracies caused by end fixture damage, numerous attempts have been made to develop the use of materials other than metal end plate fixtures. Since the preponderance of level instruments being produced at this time incorporate extruded aluminum frames, the use of dissimilar materials, such as plastic, have given rise to a number of manufacturing problems. Permanent securement of plastic end fixtures to metal frames has been troublesome. Orientation of the edges of end fixtures to extruded metal frames has been particularly troublesome. Because of the widely varying cross-sectional dimensions encountered in the use of extruded level frames, it has been difficult to secure plastic end fixtures to the frame in a manner such that at least a portion of the end fixture will not intersect one or more of the level working surfaces provided by the frame. This will produce inaccuracy in level measurements made with reference to the affected working surfaces.
Applicants have addressed themselves to these problems and overcome them with the level instrument of the invention. The end plate of this level is fabricated from a thermoplastic material, and can be permanently anchored to an extruded metal frame structure and is automatically oriented to the frame to accommodate variations in cross-section of the frame extrusion without intersecting or overlapping working surfaces. This has obviated instrument inaccuracies and the need for additional machining operations to remove such overlaps or intersections. The resulting unit can thereby utilize the benefits of a resilient material, such as plastic, in level instruments. The instrument may be dropped on end and subjected to a reasonable amount of rough handling without imparting permanent damage to the instrument, as has often resulted from the burring or upsetting of end edges in metal end fixtures in such a way as to intersect or overlap working surfaces. In such instances, the metal end fixtures, once damaged, often destroyed or impaired the utility of the instrument. However, with the level of the invention, minor damage to the plastic end plate through rough handling will rarely affect the instrument's life or accuracy.