Adjustable tenoning shim

Woodworking – Process – Mechanical cutting or shaping

Reexamination Certificate

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Details

C029S428000, C029S525010, C083S665000, C083S698410, C144S218000, C144S237000, C144S238000, C407S031000, C407S048000, C407S060000

Reexamination Certificate

active

06675849

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the field of woodworking. More particularly, it relates to adjusting table saw blades for cutting tenons in wood.
BACKGROUND OF THE INVENTION
One of the most universal woodworking joints is the mortise (the female part of a joint) and the tenon (the male part). While some jigs for making tenons do exist, they are not widely used for several reasons. First, the tenon is generally a joint that is unseen and, therefore, going to the trouble of making tenons is often not justifiable to the professional or amateur woodworker. Also, there is no convenient jig system which makes precisely fitting pairs of mortises and tenons on a repeated basis.
To properly make a tenon and mortise type joint requires two very separate operations. Firstly, cutting out the mortise from a first work piece and secondly, cutting a tenon from a second work piece. Mortises are easily and efficiently produced with a hollow chisel mortiser (either a dedicated one or a mortiser that fits on a standard drill press) or with a plunge router. The problem has always been the easy and efficient production of the tenon and, specifically, controlling the thickness of the tenon. While there are prior art jig systems such as the three-dimensional router-based system sold under the name “Multi-Router.” This prior art system is claimed to be able to produce matching mortises and tenons; however, that system costs roughly $3,000-beyond the reach of most woodworkers.
Many traditional uses for tenons have been circumvented by modern technology, such as plate joinery, also called “biscuit” joinery, and the development of the router- and shaper-based machining of stiles and rails, which produces essentially a stub-tenon in a groove instead of a true mortise and tenon joint. However, a true tenon and mortise joint is a superior joint and the serious woodworking hobbyist and professional woodworker desire a tool that would help them make more consistent tenons. Well-fitting tenons are a matter of pride for woodworkers. Currently, accurately dimensional tenons are also a source of consternation and anxiety due to the difficulty in their creation.
Because tenons have long (generally over an inch) and broad surfaces, maintaining a consistent thickness over the entire body of the tenon is problematic. Using currently known methods, each face of the tenon (called a “cheek”) is machined separately, which creates the opportunity for dimensional error in the width of the tenon.
Using prior art systems, when woodworkers first try to cut a tenon on a table saw (especially if they are untrained), they usually try laying the board down on its side and using “dado blades” (multiple cutting blades and shimming blades ganged together that remove a lot of material in one pass) to remove the material and leave the cheeks. This is quick because the shoulder cuts (the cuts that determine the length of the tenon) are made as the dado blade passes under the tenon, removing the material and revealing one cheek. But this operation requires two passes, one for each cheek, and is not accurate and leads to very rough cheeks, which either have to be hand-planed down or left rough, resulting in a less secure joint.
Woodworkers know that when they make doors, the machining must all be done with a chosen face of each part referencing the cutting tool. This is so that any error created by small differences in the thickness of the parts or misalignment of the cut will end up on the same side of each board cut.
Under another prior art method, tenons are often cut on a table saw using one reference face of the work piece against the fence for cutting one cheek, then flipping the work piece around and using the second face as a second reference face for cutting the second cheek. Because different reference faces are used, this method invites error and results in inaccurate tenon widths.
Under existing prior art methods, making tenons is more accurate when the operator pays attention to which face of the board is against the fence, or guide, for each cut and uses the same reference face when making all the tenon cuts. However, this method requires moving the fence and fine-tuning the thickness of the tenon by minute adjustments of the table saw fence. It is a tedious method based on trial and error and much material often ends up being wasted before the right fence adjustment is located.
While some prior art shows spacers between cutting blades, none of them would be effective in cutting a true tenon. It is well known in the art to place a spacer between dado blades. For example, U.S. Pat. No. 6,367,524 B1 issued to Brewer discloses an adjustable bit having a spacer between two cutting blades. However, as the abstract of Brewer discloses, the adjustable bit with cutting blades is for cutting shallow tongues or grooves. The adjustable bit disclosed in Brewer cannot be used to cut true tenons because the router disclosed lacks sufficient cutting power to remove a cheek with the depth required to form a true tenon. Further, the spacers disclosed in Brewer are exposed to wood chips and contaminants which can lodge between the spacers.
There are also other prior art systems showing spacers between cutting blades such as U.S. Pat. No. 5,368,079 issued to Benway, U.S. Pat. No. 5,316,061 issued to Lee and U.S. Pat. Nos. 4,589,458, and 5,309,962 issued to McCord Jr. et al. However, these prior art systems all relate to dado type blades and adjusting the distance between the blades to change the width or the size of the cut, slot or groove to be made. The adjustment of the blades determines how much material will be removed and not the amount of material to remain between the cuts made by the cutting blades.
One attempted solution to the problem of making tenons is to put spacers or shims between two table saw blades corresponding to the desired tenon width. The woodworker places custom made spacers of steel and/or brass between the two saw blades and makes test cuts of the work piece on a trial and error basis until the desired tenon width is achieved. This trial and error method has many drawbacks. It can be cumbersome due to the repeated addition and removal of individual shims of numerous different size onto the thread of the table saw arbor. Each individual spacer needs to be assembled separately on the arbor with some of the thinner spacers often being caught between the threads of the arbor during assembly. Further, the spacers are specially machined from steel and/or brass adding to the expense of the spacers. Also, if thin individual steel spacers are used and they do not abut each other in a flat and flush manner, they can spring and flex causing a spring effect that makes the spacing between the cutting blades inconsistent, unreliable and unrepeatable. Additionally, if spacers are placed individually on the arbor, they can be exposed to contaminants such as wood chips, sawdust or dirt which may lodge between the spacers and alter the desired spacing between the spacers.
What is desired is a simple adjustable tenoning shim for use between cutting blades for cutting tenons that is adjustable over a wide range of tenon sizes, is easy to use, easy to assemble, is not susceptible to contaminants and can be used to make accurate tenons on a repeated and consistent basis. What is also needed is a simple adjustable tenoning shim that permits the woodworker to cut an accurate tenon and remove both cheeks after a single pass through the cutting blades using a single reference surface.
With the present invention, only one face is referenced because only one pass is needed to cut the tenon cheeks. And once the adjustable shim has been set and a fence adjustment has been found for a given tenon size, the same shim adjustment can be used and the fence can be dialed back to the same position the next time a given tenon size is required. This is because the adjustable shim, rather than the table saw fence, is being used to size the tenon. Instead, the fence is just being used to locate and position the tenon relative to t

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