History of the Leg Vise
The leg vise was very popular in 19th century America and many examples exist to this day. Leg vises are characterized by their vertical jaws operated by a single screw, placed below the clamping area and above the lower fulcrum part of the jaw. The clamping screw was typically placed around 9 inches from the top of the bench and the fulcrum point was located as close to the floor as possible. A horizontal beam was placed near the bottom of the jaw and slid through a mortise chopped into the bench leg. The leg vise can be visualized as a giant wooden hand screw clamp placed vertically .This form of vise probably evolved from the blacksmith’s iron post vise.
Leg vises typically use the left front leg of the bench as the rear jaw of the vise. The screw of the vise was either threaded into the leg or a separate wooden vise nut was attached to the bench leg. In some instances the leg vise is mounted on sliding rails on the bench face to allow it to be moved to the most advantageous location. The top of the jaws may be flush with the bench top or may be raised above it to allow clamping of irregular shaped parts or allow easier carving.
The biggest issue with leg vises is how to keep the jaws parallel to allow proper clamping. When the screw is tightened both the top and bottom of the jaw are pressed against the leg. Without some method of supporting the bottom of the vise jaw it will angle so severely that clamping will be impossible. (Unless you are clamping a tapered part.)
To solve this issue the horizontal beam mounted at the bottom of the vise jaw has a number of closely spaced holes place in it. This allows a peg to be inserted into the hole which most closely matches the thickness of the work piece. When the work piece is clamped the peg then bears against the bench leg to keep the vise jaw more or less parallel to the leg. The peg must be moved to another hole when clamping thicker or thinner stock.
Through the years there were various alternatives developed to replace the horizontal beam and peg to keep the jaw parallel to the leg. Perhaps the simplest method is to place a block of wood, the same thickness as the work piece, between the vise jaw and the leg. Steel ratcheting bars have also been used to create an adjustable lower fulcrum. The best know device used to keep the jaws parallel is the cast iron scissors mechanism that is mounted below the vise screw. It uses two arms that are pinned to the jaw and leg at the top and connected to each other with a pin at the mid-point of the arms. The bottom of each arm rides against metal plates inset into the jaw and leg. This mechanism allows the jaws to be held parallel regardless of how wide the vise is opened. Another variant is the chain parallelism mechanism. This uses a roller chain (similar to bike chain) to automatically keep the jaw parallel to the leg through a system of sprockets that guide the chain from a mounting point on the jaw near the screw to the end of the horizontal beam.
Advantages of Leg Vise
The biggest advantage to the leg vise is the deep throat of the vise. The throat is the distance from the top of the bench to the screw. The large throat allows wide boards to be secured so the edges may be worked. Very long boards can be secured if a board jack is used to support the un-clamped end. Long boards may be clamped vertically by offsetting the board to one side of the vise screw. If the board is very wide, additional clamping may be required to secure the side opposite of the vise.
Disadvantages of Leg Vise
The most common complaint about leg vises is the necessity to bend over and move the peg in the lower horizontal beam every time a different thickness of work is clamped. The deep throat of the leg vise reduces the amount of clamping force that may be applied to the work. The fact that the vise jaw has some amount of play and it is difficult to get the jaw exactly parallel to the leg means that both the jaw and the leg need to have a leather facing (or other compliant material) affixed to the clamping areas. This provides extra friction and accounts for any lack of parallelism. Another complaint is the lack of quick action on the vise screw. You must crank the clamp handle a lot to adjust the vise for various thicknesses of material. Having a greasy screw that may contact the work piece is also a commonly known disadvantage to the leg vise.
VX20 Leg Vise
The VX20 Leg Vise
The Hovarter Custom Vise VX20 leg vise mechanism is the only quick action leg vise mechanism on the market. It utilizes a hardened steel smooth clamp shaft instead of a threaded rod like other leg vise hardware. The smooth clamp shaft does not require oil or grease for lubrication and won’t soil your beautiful work. When unclamped the vise jaw may quickly and effortlessly be slid in and out to suit the width of the work that needs to be clamped. Once the vise jaw is placed against the work and the lower peg placed in the correct hole a quick turn of the clamp handle locks the vise tightly. You can apply as much or as little force just like a traditional screw. If you don’t like bending over to move a peg, create the ultimate leg vise by coupling the VX20 with the X Link scissors mechanism. The X Link is a modern adaptation of the cast iron scissors mechanism. The X Link takes up much less space than the traditional cast iron scissors mechanism and uses a spherical bearing to make installation easy. The X Link also supports the weight of the vise jaw making the action incredibly smooth and easy. If you would like another option instead for holding the jaw parallel, consider the chain parallelism mechanism. A modern version of this mechanism is offered by Ancora Yacht Service by Jim Ritter.
Installation of the VX20 could not be simpler. Just drill a hole through the bench leg to accept the clamp shaft and fasten the vise mechanism to the rear of the leg with 4 screws. A bearing is mounted to the front of the leg in a counter-bored hole. The VX20 can be outfitted with a metal hand wheel or a more traditional wooden hub and tommy bar style handle. You may also construct a handle of your own design to really give your vise and work bench the total custom treatment.
The VX20 leg vise is not only quick action it also features quick removal. By simply removing a quick release pin the entire vise jaw may be removed and the clamp shaft retracted flush with bench leg. This feature may come in handy if you need to clamp a large door or other large panel to the front of the bench. You can also create special clamping jaws to handle special situations in your shop such as clamping tapered legs or round work.