Woodworking – Process – Mechanical cutting or shaping
Reexamination Certificate
2001-08-31
2003-08-19
Bray, W. Donald (Department: 3724)
Woodworking
Process
Mechanical cutting or shaping
C083S013000, C083S761000, C083S821000, C144S085000, C144S144100, C144S329000
Reexamination Certificate
active
06607016
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to a jig for cutting interlocking joints, and more particularly relates to a jig for use with a hand saw for making hand-cut tails and pins to form a dovetail joint.
BACKGROUND OF THE INVENTION
Dovetail joints are considered to be the hallmark of a master woodworker who has acquired a significant level of skill. Dovetail joints are also a mark of quality and attention to detail that many people look for in high-quality furniture. This is because a dovetail joint requires very accurate and consistent workmanship in order to fit together properly. However, creating tight-fitting, accurate dovetail joints requires skill and patience sometimes beyond the amateur woodworker. The greatest difficulty in cutting dovetails is making the initial cuts in the pin and tails at the correct locations and at matching angles.
Numerous jigs have been devised to aid woodworkers in making hand-cut dovetail joints. Many of these dovetail jigs have been made completely of wood by woodworkers themselves. For example, a popular “homemade” dovetail jig typically consists of a several blocks of wood glued together with at least one edge cut at a predetermined angle. These wooden jigs are mainly used as marking gauges to lay out the dovetail joint but can be used to guide a saw. The jig is positioned in a first orientation on the board and used to guide the saw to make cuts for the tails. Next, the jig is positioned in a second orientation on a mating board and used to guide the saw to cut the pins. Although, jigs make it easier for the average woodworker to make accurate cuts when cutting hand-made dovetails, such homemade jigs have several limitations. One limitation of these wooden jigs is that the woodworker has to manually insure that the saw remains in contact with the guide face. Because these jigs have no mechanism to hold the saw against the guide face, it is very easy for the saw to “wander” from the guide block, especially when cutting dovetails in hardwoods. Any wander by the saw from the guide block reduces the accuracy of the cuts, which at a minimum, requires additional time and effort to obtain a properly fitting joint. Another limitation of these jigs is that the entire guide surface contacts the saw blade. This results in significant damage to the guide face from the saw teeth. Therefore, as the guide face becomes damaged, the accuracy of the cuts, and the quality of the dovetail joint decreases significantly. Furthermore, because the saw teeth contact the guide face, the saw is subject to additional wear, which prevents the saw from making a clean cut.
One effort to overcome the limitations of the homemade jig uses wooden guide faces positioned above the edge of the workpiece. This prevents the saw teeth from rubbing the guide face. This approach, however, does not secure the saw blade flush against the guide face during the entire cut.
Thus, there is a need for a jig for use in hand cutting dovetail joints that automatically engages the saw blade and ensures that the saw blade remains properly positioned during the cut, preferably while facilitating saw movement.
SUMMARY OF THE INVENTION
This invention is a jig having a guide block and a repositionable clamp for use with a saw for hand cutting tails and pins on the ends of mating boards to form a dovetail joint. The guide block provides two guide faces and two orthogonal wing surfaces for positioning against a face and end of a board to orient the guide faces either: (a) square to the end of the board and at an angle to its faces for cutting the tails, or (b) square to the faces of the board and at an angle to the end of the board for cutting the pins. This invention improves prior dovetail guide block designs by providing a pair of magnets within the body of the guide block, each of which are covered by a low friction pad. The magnet underlies the low-friction pad and firmly engages the saw to keep it in contact with the guide face throughout the cutting operation. The repositionable clamp may be attached to the guide block for clamping it to the board in either of the two alternative positions.
Both the guide block and repositionable clamp may be made from segments of extruded aluminum. In one embodiment, the guide block body extrusion has four generally planar sides, which are joined to form a tube having a substantially square cross section. The guide block also contains a pair of substantially orthogonal planar surfaces, or “wings,” oriented parallel to two adjacent sides of the guide block and connected at one corner for supporting the guide block on the end of the workpiece. The extruded body also includes a generally round channel positioned inside the square tubular guide block adjacent to the reference wing-bearing corner for receiving a pair of disk-shaped magnets.
A recess is milled into each reference face of the guide block to receive one of the low-friction pads. The depth and position of the recessed channel is such that the low friction pads extend past the guide face by a distance equal to or slightly more than the tooth set of the saw to be used. This offset insures that the saw is placed in a repeatable cutting location with respect to the guide block and also prevents the saw blade from damaging either the low-friction pads and the guide block.
The invention also includes a method of hand cutting the tails and pins of a dovetail joint using a guide block having at least one angled guide face and having a magnet embedded in the plane of the tapered guide face and covered by low friction pad to ensure that the saw slides smoothly across the guide face. The method begins by first laying out a series of tails and pins in the tailboard and pinboard, respectively. Next, the guide block is oriented in a first position on the tailboard, such that the guide face forms an angle with the end of the tailboard. The guide block is placed on the tailboard so that the guide face is resting on the first tail line. This ensures that the friction pad is positioned on the waste side of the tail line. The saw is then placed against the friction pad such that the teeth are positioned below the friction pad and the saw is fully engaged by the magnet. The tail is cut by sawing down to the depth line. The procedure is then repeated for each addition tail. Next, the guide block is positioned in a second orientation on the pinboard such that the guide face is square to the end of the pinboard and forms an angle with the faces of the pinboard. The saw is then positioned against the low friction pad and engaged by the magnet in the guide face, which insures that the saw is fully engaged with the guide face during the entire cut. The procedure is then repeated for the remaining pins.
REFERENCES:
patent: 3695318 (1972-10-01), Maury
patent: 3861665 (1975-01-01), Wynn
patent: 4462440 (1984-07-01), Dolfi
patent: 4632159 (1986-12-01), Glasgo
“Dovetail Jig”, Popular Woodworking, Dec. 2000, No. 19, p. 47-49.
“Methods of Work”, Fine Woodworking, Feb. 2001 No. 147.
JM-1 Jointmaker, Bridge City Tool Works Catalog, p. 5.
“Making Hand-Cut Dovetails”, American Country Furniture, Nick Engler and Mary Jane Favorite, p. 112-115.
Bray W. Donald
Kilpatrick & Stockton LLP
Lee Valley Tools Ltd.
Pratt John S.
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