Cutting – With means to convey work relative to tool station – With projections on work-carrier
Reexamination Certificate
2001-07-02
2003-06-17
Peterson, Kenneth E. (Department: 3724)
Cutting
With means to convey work relative to tool station
With projections on work-carrier
C083S438000, C083S477200, C144S245600, C144S425000, C144S253100, C198S749000
Reexamination Certificate
active
06578461
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to cutting apparatus and method comprising means to convey a workpiece relative to a tool station; and more specifically relates to a pusher preferably built into a rip fence for a table saw.
2. Background Information
Table saws having a portion of a motor-driven circular blade extending upwards through a slot in a saw table are commonly used for rip-sawing narrow strips of wood from a large stock piece. This practice is inherently dangerous and the danger is somewhat reduced by the use of any one of a number of known rip fences. Each of these fences has a straight, flat guide face and can be clamped or locked to the saw table so that the guide face is parallel to the plane of the saw blade. The simplest rip fence may consist of a straight, flat, wooden board clamped to the top of the saw table with individual clamps. The usual, mass-produced, rip fence is fabricated from steel. It can be slid toward or away from the blade on guide rails attached to the front and rear of the saw table. The front of this fence is equipped with a lever for locking both front and rear ends of the fence to the guide rails when depressed.
The manner of rip-sawing wood by hand is the same no matter what kind of rip fence is utilized. The woodworker adjusts the distance between the guide face and the adjacent side of the saw blade to equal the width of the piece he wishes to rip off. He clamps or locks the fence to the saw table in the desired position with the fence parallel to the saw blade and turns the saw on. The woodworker then begins to advance the stock piece of wood into the rotating saw blade by pushing the stock with both hands. As he does this, he must simultaneously hold the stock piece firmly down on the saw table while guiding one straight edge of the stock piece along the rip fence's guide face. That is, he must press the stock piece down on the table and also push it laterally against the rip fence as he advances the stock piece toward the saw blade. To keep his fingers from being cut by the rotating blade, he must keep them a safe distance from the blade at all times. If the desired width of cut exceeds about two inches, the woodworker may feel confident enough to push the rear end of the wood past the blade with one or more fingers of his or her dominant hand, while reaching beyond the tool with the other hand so as to exert pressure on the cut end to hold it against the table and against the guide face of the rip fence. As the blade cuts through the wood, his finger (or fingers) must enter the narrow space between rip fence and saw blade as he pushes the wood past the blade. When using this technique to rip off very narrow pieces, however, there is always the danger that the blade will cut a finger.
While rip-sawing pieces of any width off a stock piece, an accident called “kickback” can occur if the woodworker accidentally allows the already cut end of the stock piece to angle away from the guide face by even a tiny amount. If the cut end is caught by the far, or outfeed, end of the saw blade, where the blade's teeth are rising through the table's slot, the rising and backward-moving teeth snag the wood piece, kicking it off the table and towards the woodworker. The hand grasping the cut end often is pulled back into the saw blade and badly lacerated by the rotating blade. A wood piece may be kicked back with such force that it may itself lacerate a hand or drive splinters into the hand.
To minimize the risk of cutting his hands, the experienced woodworker may use a push stick instead of his fingers to advance the stock piece. As the push stick traverses the narrow corridor between saw blade and fence, however, it may accidentally contact the rotating blade. When this occurs, the push stick can itself be kicked backward into the hand holding it. This sometimes results in a lacerated hand or, at the very least, a bruised one. Push sticks have one major disadvantage—when using one it is difficult to keep the stock piece pressed laterally against the guide face of the fence while it is being pushed forward and past the blade. If the stock piece is allowed to drift off the fence's guide face at the infeed end, the ripped piece will not have a uniform width along its length; if the stock is allowed to drift off that guide face at the outfeed end, a kickback may occur.
Commercially available hold-down devices, such as those sold under the trade names of Shop Helper (™), Ripstrate(™), or Leichtung(™), can be clamped to a rip fence to aid in rip-sawing wood. These devices tend to hold the stock piece down and press it laterally against the rip fence. However, a push stick must still be used to advance the wood into the blade toward the end of the cut. The arms of the various hold-down devices traverse the corridor between rip fence and saw blade. The arms, therefore, are obstructions that prevent a push stick from pushing the wood all the way past the saw blade. When rip-sawing with one of these devices clamped on the rip fence, the woodworker pushes the stock piece as far into the blade as he safely can with his hands or a push stick. Then, to complete the cut, he must walk around to the outfeed end of the table saw, grasp the cut end and pull the stock piece through the saw blade.
There are other devices, such as featherboards, which can be used in both horizontal and vertical positions to assist in the ripping operation. A horizontal featherboard can be clamped to the top surface of the table saw to push the stock piece against the guide face of the rip fence. It can only be positioned at the infeed end of the saw (if one is positioned at the outfeed end, it will squeeze the saw kerf and may cause a kickback). Vertically positioned featherboards can be used to hold down the stock piece down on the table. These may be placed at both infeed and outfeed ends. These vertically positioned featherboards usually are clamped to the rip fence, where they obstruct the passage of a push stick. A featherboard will help hold the stock piece down on the saw table. It cannot be set up to press the piece laterally against the rip fence, however. Because featherboards are clamped to the rip fence, they also obstruct the passage of a push stick.
Expensive, motor-powered, rubber-tired feeders may be purchased for rip-sawing wood. A power feeder will simultaneously advance the workpiece while holding it down and pressing it laterally against the rip fence's guide face. They work well, but can require considerable set-up and adjustment time for accurate rip-sawing. Commercial woodworking shops find power feeders invaluable for safely rip-sawing a large number of pieces of identical width, but most amateur woodworkers cannot afford them. Moreover, a woodworker who does use one may prefer to use a simple push stick when rip-sawing only one or two pieces. To rip-saw off very narrow pieces, the power feeder sometimes must be lowered down so that it straddles the saw blade. During subsequent rip-sawing the blade will cut partly into some of the rubber tires.
Although the use of a table saw is of considerable concern for the invention, and is generally used as an example hereinafter, it may be noted that similar concerns arise with many other power woodworking tools in which a workpiece is held against a guide member as it is conveyed along a feed direction to a tool station. For example, a shaper, which commonly has a tool bit spinning at four to five times faster than a table saw blade, presents many of the same hazards as are encountered in the use of a table saw.
Notable among patent references in this area are the following:
In U.S. Pat. No. 5,662,019 Denman teaches a workpiece pusher that is retractable from a workpiece-engaging position by rotation about an axis parallel to a workpiece feed direction. It is notable that if Denman's pusher is allowed to rotate while a workpiece is being sawn, the rotation tends to push the workpiece away from the rip fence. Moreover, if Denman's pushe
Kiewit David
Peterson Kenneth E.
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