1. Field of the Invention
This invention relates to the field of abrasive or grinding wheels, and in particular this invention relates to grinding wheels that facilitate observation of a workpiece during grinding.
2. Background Information
Abrasive (i.e., grinding) wheels are widely used on conventional grinding machines and on hand-held angle grinders. When used on these machines the wheel is held by its center and is rotated at a relatively high speed while pressed against the work (i.e., workpiece). The abrasive surface of the grinding wheel wears down the surface of the work by the collective cutting action of abrasive grains of the grinding wheel.
Grinding wheels are used in both rough grinding and precision grinding operations. Rough grinding is used to accomplish rapid stock removal without particular concern for surface finish and burn. Examples of rough grinding include the rapid removal of impurities from billets, the preparing of weld seams and the cutting off of steel. Precision grinding is concerned with controlling the amount of stock removed to achieve desired dimensional tolerances and/or surface finish. Examples of precision grinding include the removal of precise amounts of material, sharpening, shaping, and general surface finishing operations such as polishing, and blending (i.e., smoothing out weld beads).
Conventional face grinding wheels or surface grinding wheels, in which the generally planar face of the grinding wheel is applied to the workpiece, may be used for both rough and precision grinding, using a conventional surface grinder or an angle grinder with the planar face oriented at an angle up to about 6 degrees relative to the workpiece. An example of a surface grinding operation is the grinding of a fire deck of a bimetallic engine block, such as disclosed in U.S. Pat. No. 5,951,378. Conventional face grinding or surface grinding wheels are often fabricated by molding an abrasive particulate and bond mixture, with or without fiber reinforcements, to form a rigid, monolithic, bonded abrasive wheel. An example of suitable bonded abrasive includes alumina grain in a resin bond matrix. Other examples of bonded abrasives include diamond, CBN, alumina, or silicon carbide grain, in a vitrified or metal bond. Various wheel shapes as designated by ANSI (American National Standards Institute) are commonly used in face or surface grinding operations. These wheel types include straight (ANSI Type 1), cylinder wheels (Type 2), recessed (Types 5 and 7), straight and flaring cup (Types 10 and 11), dish and saucer wheels (Types 12 and 13), relieved and/or recessed wheels (Types 20 to 26) and depressed center wheels (Types 27, 27A and 28). Variations of the above wheels, such as ANSI Type 29 wheels, may also be suitable for face or surface grinding.
A drawback associated with conventional face grinding or surface grinding wheels is that the operator cannot see the surface of the workpiece being ground during the actual operation; the operator can only see material that is not covered by the wheel. It is often difficult to carry out a precise operation without repeatedly inspecting the work in progress to more closely reach an approximation to the desired result. Hand-held tools such as angle grinders, cannot be re-applied precisely so that repeated inspection is not a good option for careful work.
A wheel having perforations becomes semi-transparent when spun at a moderate to high speed because of the persistence of image on the retina in the human eye; the “persistence of vision” effect. The image seen through a perforated spinning wheel is further enhanced if there is a contrast in light and/or color between the spinning wheel and its background and/or foreground. To increase the width of the “window” or see-through viewing effect when a wheel is spun, perforations are usually designed to overlay each other. Abrasive sanding wheels that make use of this phenomenon are shown, for example, in U.S. Pat. Nos. 6,159,089; 6,077,156; 6,062,965; and 6,007,415; which are fully incorporated by reference herein.
Because of the presumed catastrophic consequences of monolithic resin/grain composite wheel breakage and/or protrusions into large apertures, the use of such “windows” to date has been limited to multiple component metallic-bodied cutting blades and/or flexible sanding wheels.
Thus, a need exists for an improved tool and/or method for surface grinding.