Patent Application
20060054153
This invention relates to the provision of a concrete cutting chain saw that can be powered by conventional single phase household electric power.
Historically, concrete cutting saws have been diamond impregnated circular blade cutting saws. Such saws require large circular blades, e.g. a 16″ in diameter blade that has a maximum cutting depth of e.g. 6″. Further, a configuration of a cut made by the circular saw blade is curved with a shallow lead in cut and a shallow exit cut. Thus, a through cut of e.g. 10″ will require a shallow lead in and shallow exit cut that extends beyond the 10″ through cut, at both ends, by several inches.
These and other factors have prompted the development of a chain saw type concrete cutting saw. The configuration of the cut can be made square and thus provide a clean cutout of a square or rectangular shape as may be desired, e.g., for providing a window or door opening in a concrete wall.
A chain saw type concrete saw has several concerns. The chain is comprised of alternating center drive links and pairs of opposing side links. Certain or all of the paired side links cooperatively carry a cutting head including a matrix block impregnated with diamond chips. This arrangement requires a thicker cut to accommodate the triple width thickness of center and side links as compared to the single thickness of a circular blade. In any event, concrete cutting chain saws have been considered to require a substantial drive motor, e.g. ranging from a low of about 5 horsepower motor to as high as 9 horsepower motor. Motors having such substantial horsepower are primarily hydraulic and gas motors, with some at the low end of the power requirements driven by an industrial electric motor, i.e., that requires the use of a separate generator and cannot be simply plugged into a household electric outlet.
Horsepower is equated to torque and speed. For cutting concrete the prevailing view is that the speed must be maintained at an established high level. At the desired level of surface speed, the power source must generate a minimum level of torque, i.e., as necessary to drive the chain at the desired speed while cutting through the concrete. Heretofore the speed and torque considered necessary has eliminated the use of household electrical power as a power source for concrete cutting saws.
It is an objective of the present invention to provide an electric concrete cutting chain saw that can be operated on a single phase household electric power source. This is necessarily achieved by reducing the required horsepower to accommodate the electrical power output of single phase electricity. Whereas it was found that the torque cannot be reduced significantly to achieve that end, the invention challenges the prevailing view as to the chain speed requirement. The surface speed was reduced via the reduction in size of the drive sprocket. It was found that some reduction in chain speed was acceptable and surprisingly enabled the retention of sufficient torque to satisfy lesser concrete cutting demands, all at a horsepower requirement achievable with single phase electric power.
Other modifications that further assist in enhancing torque are the narrowing of the chain and bar width to allow a more narrow kerf to be cut and a reduction in the number of diamond chips (cutting implements) in the cutting blocks of the saw chain cutters. The latter reduces the number of diamonds that participate in the cutting action at any given time which reduces power and torque demand.
Whereas the cutting tool does not cut with the speed and power of industrial size concrete cutting saws, what does occur is the matching of the cutting capabilities of the saw to the power capabilities of a single phase electrical power source. Such provides the homeowner with an affordable, smooth running and efficient electric powered concrete cutting tool that has not been heretofore considered achievable as a homeowner type tool.
As a further innovation, the lower powered concrete cutting chain saw is alternatively provided by the conversion of existing single phase power tools e.g. an angle grinder. An angle grinder has a drive shaft that drives a grinding disk. The disk is removed and replaced with a drive sprocket. In a particular version of the grinder, a feature that enables multi-positioning of a front handle for the grinder provides a mount for a saw chain housing and guide bar (on which a saw chain is mounted). The size of the sprocket dictates the linear speed of the chain and is selected to satisfy the criteria for concrete cutting.
The invention will be more fully understood and appreciated with reference to the following detailed description and accompanying drawings.
Reference is made to
The power head 12 includes a body 16 having a handle portion 18. An electric motor inside the housing is connectable and powered by a single phase electric outlet via cord 20. The electric motor through actuation of the trigger switch 21 (see
The power head of the illustration is provided with opposing threaded holes [24] into which fastening bolts 24 are inserted to secure the components of the conversion kit 14 to the power head 12. (In a different adaptation of the power head 12, the bolt holes [24] may be used to secure a front handle, e.g. when adapted to receive a grinding disk or wheel secured to the drive shaft 22.) The conversion kit includes (as a separate component) a drive sprocket mounted to the drive shaft 22 which can be best seen in
A removable cover 32 is secured to the bracket 28 and is removed as seen in
The tool as described above, i.e., the combination of power head 12 and conversion kit 14 enables the replacement of the kit, e.g., with a grinder wheel for use, e.g., as an angle grinder as previously indicated. Quite readily, the mounting bracket and chain saw components can be removed by removal of bolts 24 and then replacement of sprocket 26 with a grinder disk or wheel. In this event a front handle (forward of rear handle 18) would be secured into one of the threaded holes 24. Although not shown, the rear handle 18 in some versions of power heads that are convertible to a chain saw as described, can be rotated in either rotative direction, e.g. 90° around a break line indicated at 44 in dash line. This is beneficial for orienting the tool to the task, e.g., for grinding or cutting vertically as opposed to horizontally.
The invention is further explained with reference to the chart of
As previously explained and as illustrated by the chart of
The inventors departed from the conventional wisdom and conceived the idea that horsepower could be reduced without satisfying torque if the rpms were reduced. The smaller saw and the type and frequency of concrete cutting by e.g. a homeowner renders speed of cutting less important. As illustrated in the chart, the horsepower was reduced, not by reducing torque but by reducing chain speed. It was determined that the reduction in rpms should create a surface/linear speed of the chain of no greater than about 4,800 feet/minute. The unexpected result was the favorable matching of speed and torque to the less abusive jobs of the homeowner. The homeowner can power the saw with single phase household current and achieve a smooth yet adequate cutting performance at a cost that is a fraction of that required for the higher powered industrial/professional cutting tools.
The invention at least in part is believed to be the matching of a concrete cutting chain saw design to the power capabilities of household current. In the course of this development, there has been a further realization that because tool abuse is lowered, the cutting links themselves can be made smaller and thereby reduce the kerf width which in turn reduces torque demand. Still further, again because speed is not a primary objective of a homeowner, the number of exposed diamond chips (cutting implements) per cutting block can be reduced which again reduces torque demand.
The interrelationship of these changes has produced a unique concrete cutting chain saw that provides a desirable match up to the needs of a typical homeowner having concrete cutting tasks. Those skilled in the art will conceive of further alterations and variations without departing from the invention. Accordingly, the above disclosed embodiment is included as an example of but one embodiment, albeit a preferred embodiment, of the invention. The invention is not to be limited to that of the disclosure but is intended to be encompassed by the definition of the claims appended hereto, the terms of which are to be given a broad interpretation as used in the art.
