Patent Application
20070297843
The present invention relates to tools for applying mastic and especially to flat finisher tools for applying mastic to drywall joints.
Flat finisher tools are well known in the housing construction and drywall industries, and are used to apply a coating of mastic to conceal the joints between drywall panels. An example of a typical flat finisher tool is provided by U.S. Pat. No. 2,984,857, which is incorporated herein by reference. Conventional flat finisher tools consist of a container for holding a supply of mastic, with an opening for dispensing the mastic. A flexible trowelling bar is attached to the tool for shaping and smoothing the surface of the applied mastic. As the mastic is dispensed, the trowelling bar flexes over the applied mastic to form a concave curve that shapes the mastic into a layer that is thick in the center and is feathered or thin at the edges to blend into the surface of the drywall.
The curvature of the trowelling bar and, therefore, the thickness of the applied mastic, is indirectly controlled by a cam that regulates the pressure exerted by a leaf spring on the trowelling bar. Actuating the cam increases the pressure on the leaf spring, which increases the pressure on the trowelling bar to reduce its curvature and produce a thinner layer of mastic. However, the leaf spring often becomes distorted after repeated use, which reduces its effectiveness in controlling the curvature of the trowelling bar.
The trowelling bar typically comprises a normally flat blade mounted in a brass rod that serves as a blade guide. Because the curvature of the trowelling bar depends on its ability to flex over the mastic, numerous slots are cut perpendicular to the longitudinal axis of the brass rod to increase its flexibility and ensure that the blade guide will arch or curve properly as it passes over the mastic. Forming these slots requires extensive machining and adds to the expense of manufacturing the trowelling bar. In addition, the brass trowelling bar is relatively heavy, making the tool more difficult to wield and more tiring to use.
Thus, there is a need for a flat finisher tool that reduces or eliminates the reliance on a leaf spring to control the curvature of the trowelling bar. In addition, there is a need for a trowelling bar that is simpler and less expensive to manufacture, and that is made of lighter weight materials.
In accordance with the present invention, a flat finisher tool is described that comprises a container with an opening for dispensing mastic. A flexible trowelling bar is mounted on the container for shaping the dispensed mastic. A rotating cam is positioned on a rigid support connected to the container, and is directly coupled to the trowelling bar, such that the rotation of the cam controls the curvature of the trowelling bar. At least one spring is positioned between the trowelling bar and the support to bias the trowelling bar away from the cam.
Referring to
Trowelling bar 16 comprises a blade guide 18 with a slot 20 that holds a blade 22. The ends 24, 26 of blade guide 18 are received in slots 25, 27 formed in the sides of container 12, and are held in position by flanges 29, 31. Screws 28, 30 are provided at ends 24, 26 of blade guide 18 for adjusting the depth of blade 22 in slot 20. In a preferred embodiment, blade guide 18 is made of aluminum and blade 22 is made of stainless steel. In an alternative embodiment, trowelling bar 16 may have an aluminum blade guide with a composite, plastic blade or trowelling bar 16 may be formed as an integrated plastic guide/blade.
The middle portion 32 of blade guide 18 is not connected to container 12 and is free to flex relative to ends 24, 26, thereby allowing the trowelling bar to form a concave or convex curve relative to the drywall surface (not shown). The amount of curvature of trowelling bar 16 is controlled by a substantially circular cam 34, that rests on a rigid support 36. Rigid support 36 is held in place by a brace 38 that substantially spans and is attached to container 12 by bolts 40, 42 and screws 43. As best shown in
Cam 34 rotates on an eccentrically placed pivot 50 that is offset from the center of the cam and is coupled to trowelling bar 16 through a link 52. As best shown in
A pair of posts or plungers 57, 58 slide within openings 60, 62 formed in support 36, and extend between support 36 and blade guide 18. Plungers 57, 58 are provided with feet 64, 66 having rounded bottom surfaces 68, 70 that contact blade guide 18. Coil springs 72, 74 are mounted externally around plungers 56, 58 and maintain tension on link 52 as cam 34 is rotated by exerting pressure on blade guide 18 through feet 64, 66 to bias trowelling bar 16 away from support 36 and cam 34. Rounded bottom surfaces 68, 70 ensure that feet 64, 66 maintain consistent contact with blade guide 18 as the curvature of trowelling bar 16 is changed.
The curvature of the trowelling bar in the inventive flat finisher tool is not dependent on its flexibility. Cam 34 is directly coupled to trowelling bar 16, such that the action of the cam positively controls curvature of the trowelling bar. The rotation of cam 34 in the counterclockwise direction causes offset pivot 50 to move away from rigid support 36, which, in turn, causes link 52 to move upward, toward the cam. The upward movement of link 52 pulls middle portion 32 of trowelling bar 16 toward cam 34 and causes the trowelling bar to form a concave curve relative to the drywall surface. The further cam 34 is rotated in the counterclockwise direction, the greater the curvature of trowelling bar 16.
Conversely, the rotation of cam 34 in the clockwise direction causes offset pivot 50 to move toward rigid support 36, which, in turn, causes link 52 to move downward, away from the cam. The downward movement of link 52 pushes middle portion 32 of trowelling bar 16 outward and away from cam 34 to reduce or flatten the curvature of the trowelling bar. The further cam 34 is rotated in the clockwise direction, the flatter the curve of trowelling bar 16. Depending on the length of link 52, it is possible that the clockwise rotation of cam 34 may cause link 52 to push trowelling bar 16 outward enough to form a convex curve relative to the drywall surface. Springs 72, 74 operate with plungers 56, 58 and rigid support 36 to maintain tension on link 52 and ensure that cam 34 remains seated on support 36 during the operation of the cam.
Because the curvature of trowelling bar is positively controlled by the operation of the cam, the trowelling bar does not need to be machined to increase its flexibility as in conventional flat finishing tools. This permits the trowelling bar to be manufactured much more simply and less expensively, and from a wider range of materials than in conventional tools where the trowelling bar must be sufficiently resilient to flex over the mastic and form a curve. Thus, trowelling bar 16 need not be formed with a series of perpendicular slots, and may be formed of lighter materials such as aluminum and plastic rather than brass, as described above.
In a preferred embodiment, cam 34 is provided with a plurality of peripherally located flat facets 76 that function as detents during the rotation of the cam, by providing resistance to rotation as each flat facet comes into contact with the flat surface 78 of support 36. Each facet 76 serves as a different setting for adjusting the amount of curvature of trowelling bar 16 and the thickness of the applied mastic. As shown in
It will be apparent to those of skill in the art that modifications may be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited except in view of the appended claims.
The present application is a continuation of and claims the benefit of co-pending U.S. Ser. No. 11/048,967 filed on Feb. 2, 2005, the entire contents of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11048967 | Feb 2005 | US |
| Child | 11852740 | Sep 2007 | US |
