Clamps and Clamping or Cramps and Cramping
The wealth of a craftsman is determined by the number of clamps they own. You can never have too many clamps, they are what keep it all together. When one needs to hold two or more boards together as the glue dries one needs clamps. Remember it is the joint and the glue that hold the two pieces together, nails and screws are used to hold the two pieces together as the glue dries. Do not rely on the mechanical fasteners to hold the joint together, it the glue. Over the centuries certain types of clamps have evolved into common use and have recognizable characteristics. The common C-clamp or as they say in the Mother Country, G-cramps, while the word is descriptive, I being the rebellious colonialist that I am will use the common term clamps. The bar clamp, the parallel jaw clamp, band clamps and the holdfast are other common forms. I use the holdfast more than any other clamp although I seldom use it for gluing. The inventiveness of craftsman has come up with some rather clever methods of clamping and these can come in handy when gluing odd shapes.
The holdfast is by far the most versatile clamp in my shop; I have several and use them daily. The holdfast is an ancient tool of simple shape and use. Shaped like the figure 7 or an inverted L, and made of iron, the long part goes through a hole in the workbench top or sides and secures the work by a jamming action of the short leg contacting the stuff and holding it to the bench. The long shaft goes through the hole and the pad on the short bar holds the work down and the shank is bound into the hole by striking the holdfast on the top with a mallet to lock the work in place. By striking the back of the shank at the crank the holdfast is released. This tool can also be used on sawhorses or anywhere you can drill a hole to pound it in and secure your work. The pad should have a rounded face so as not to damage the stuff being worked. On soft woods, an intervening scrap block will prevent marring. Scrap blocks of wood are a good idea to use with any clamps to prevent damage to the work being clamped.
When using clamps make sure you do not over-use them, in other words you can clamp a glue joint too tight and starve the joint of glue. With hide glue as the moisture is drawn into the wood, the clamps need to be tightened slightly after a few minutes in the clamps, again careful not to starve the joint, just snug up the clamps a little. See Using Hide Glue. You can also bow or distort pieces with too much pressure.
The holdfast is one of the few metal clamps that I use, almost all are constructed of wood. While I don’t have a problem using iron or steel clamps, they are usually too heavy, will react with the hide glue and stain the stuff being glued and when you drop a heavy metal pipe clamp on a piece of antique of furniture it will leave a mark. The wooden versions are lighter, don’t react to the hide glue (I coat the clamp jaws with beeswax to prevent the glue from sticking) and will not usually mare the stuff being clamped. There is something about using wood to clamp wood together. Wooden clamps cannot exert as much pressure as there metal counterparts, but they are capable of starving a joint of glue or distorting the work, so use caution.
Some wooden clamps are not as easy to use as new modern versions but you will get use to the additional tinkering and idiosyncrasies of these tools. I have owned several wooden clamps over the years and one thing in common they all had was no pad or foot on the threaded bolt like modern clamps. Instead they have a short spike or metal nail in the center. They were intended for use with a scrap block of wood, the spike engages the scrap and pivots freely. One advantage is that it holds the scrap in place and it is easier to place the clamp in the proper position. You know how difficult it can be to hold two blocks to protect the work and at the same time position and tighten the clamp. The spike holds the scrap and the other end being wood needs no scrap block for protection.
C-clamps are built to a given size and are only adjustable by the length of the bolt travel. I have a couple of wooden c-clamps and they are handy for certain applications such as repeated gluing of the same size pieces, having a dedicated clamp for a specific purpose saves a lot of time in not having to adjust a bar clamp or parallel jaw clamp. Three pieces of wood are joined to form a C-shape. Mortise and tenon or large dovetails are used in the construction. These are usually reinforced with dowels or pegs at the corners, these clamps will exert a great deal of pressure on the ends of the arms and will test the joint repeatedly. The construction needs to be tight and strong to take the torque and pressure. The wood used to make the clamp body can be any wood that will take the pressure. The threaded bolt is best made of beech, maple or hickory that will take the pressure and repeated use. Some bolts have T or L handles on the end opposite the spike, these are for added leverage and advantage when tightening the clamp.
Bar clamps have a fixed head with the threaded bolt attached to one end of a long wooden clamp. The other end of the clamp has a moving head that can be secured anywhere along the length of the clamp, using a variety of methods to secure it such as pegs, wedges, thumbscrews, etc. These are used for clamping longer or wider work than can be accomplished with a C-clamp. One advantage of the wooden bar clamp is that the clamp itself can be used to keep boards straight and flat during clamping. One disadvantage is that the work can bow up with too much pressure, either back off on the pressure or use another wooden clamp to clamp the bow down to the bar of the clamp. Placing two bar clamps over sawhorses can make a clamping table. Also notches can be cut into the horses to accept the bar clamps, holding them upright and flat. This is handy for repeated glue-ups of large panels. Placing an additional clamp or two on top of the work also helps keep the glue up straight and flat.
Panel clamps are similar to bar clamps except they have bars on both sides and the panels are slipped in and the bars are pushed tight against the panels to hold them flat. When pressure is exerted from one or both ends via the threaded bolts, the clamping is uniform an flat, while open bar clamps will distort under pressure, panel clamp bars remain flat because of the opposing bars equalizing pressure. Some panel clamps do not have threaded bolts but use wedges against large pegs or dowels. Simple panel clamps are made by drilling a series of matching holes for the pegs or dowels along the length of the two bars. The panels are placed in the clamp and pegs or dowels are placed in the appropriate holes with room enough to insert wooden wedges. These wedges are forced against the peg and the panel and as they are driven in force the glue joints together. This method can also be used for simple bar clamps as well as between bench dogs on a workbench. I usually do not use my workbench for clamping as it will tie up the bench, but for certain work and gluing at the end of the day, it can be a handy extra clamp.
Of all of the wooden clamps perhaps my favorite is the parallel jaw clamp. Unlike the modern version with metal pivoting bolts, these are truly parallel jaws and can only clamp slight angles. Also unlike the metal clamps the back bolt does not go through the jaw but pivots in a hole. Here is how they are made. Two identical bolts are turned and threaded, one needs to be threaded all the way to the handle, the other does not need to be threaded all the way to the handle but can end a couple of inches back. Two jaws are made, usually of maple, but beech, poplar or birch can also be used, I avoid using woods with color, such as walnut or reactive woods such as oak. The holes are laid out on both pieces on the inside of the jaws. On one a hole is drilled larger than the bolt threads to allow it to pass through, this is drilled toward the front of the jaw. Another hole is drilled, the same size but not all of the way through the jaw at the back. On the other jaw two holes are drilled and threaded. The bolt that is threaded all the way to the handle is threaded through the back hole and into the blind hole on the opposite jaw. The other handle is passed through the larger hole and threaded into the tapped hole in the opposite jaw. The handles or bolts are adjusted to about the same width of the jaw and then there is an easy way to make adjustments. Grasp one handle in one hand and the other in the other and start cranking them in a circular motion in front of you. Turning or cranking the clamp one way will open the jaws and cranking in the other way will close the jaws. Adjust the clamp to fit what is being clamped and tighten the front bolt or handle. Then by advancing the back bolt into the threads it forces by leverage the tips of the jaws together. The adjusting is always done with the back bolt, which has a better leverage advantage.
Tourniquet and windlass clamps are great for chair construction and working on round or irregular shaped forms. The tourniquet is simply a rope, band or strap that encircles the object and is tied at the ends. A stick engages the band and by twisting shortens the loop and tightens upon what ever it is wrapped around. Once proper tension is achieved, the stick is prevented from unwinding and the work allowed to dry. The windlass clamp does the same thing, but instead of a simple stick, the windlass mechanism, made of wood, has a take up wheel, an advanced handle and a locking ratchet that prevents the loop from loosening. Used for barrel and wheel construction, smaller versions were employed by craftsman to glue up chairs, table aprons and other round, oval, square or irregular shapes.
Wedges and fixed clamps are simple tools that provide a sure clamp at a given dimension. The fixed clamp is usually a flat piece of wood with a large notch made in one long edge. Enough wood is left on each end of the notch to provide enough strength so as not to brake. The inside of the notch is slightly larger than the wood being clamped. The additional space is filled by a wedge, which when firmly driven between the clamp and the work, adequate pressure is concentrated on the edge of the stuff being glued.
Press clamps are enclosed frames with threaded wooden bolts placed in strategic locations and tighten down against the frame. Used mainly for veneer work, several frame or press clamps can be employed to exert pressure in the center of panels. These are frequently used with cauls, which are heated and then used to exert pressure on the veneer to affix it to the groundwork. Able to span wide reaches, press clamps can apply pressure where all else but go bars fall short.
Cam clamps are made in a variety of shapes but the main clamping mechanism is a cam. This is an off centered circle shape, usually with a handle that when turned causes the offset center to exert more pressure against the work. Cams do not have much travel, in other words they can only move a short distance, however they can exert a great deal of pressure. Cams can be used for delicate work and are finely adjustable as to the pressure they apply.
Go bars are simple clamps that can apply pressure in areas that most clamps can’t reach. They are made of springy straight grained wood such as hickory, osage orange, ash or white oak that are used to clamp by being bowed between the work bench and the ceiling, being slightly longer than the distance from the workbench to the ceiling or a ceiling beam. By bowing these thin sticks of wood and catching one end to the ceiling and the other to a scrap block of wood above the work being clamped down to the bench. Particularly handy for veneer repairs in the center of tabletops where other clamps cannot reach, these tools can exert pressure, and to increase pressure extra blocks of wood are stacked and the bow flexing will cause more pressure down on the stuff being glued.
Pinch dogs or Joiners dogs are also handy tools for clamping. These are used where the holes made by the points do not show. These are stout iron staples with the points having inside tapers. When they are pounded into the wood they pinch the two pieces together allowing the glue to dry.
When it comes to clamping, craftsmen have employed everything for warmed sand filled bags, large heavy weights, clothespins and string to secure work as the glue dries. There is no lack of ingenuity in the use of almost anything to assist in the clamping process.