There is one inescapable fact in woodworking – you always need one more clamp than you have.
Often, when setting up shop, the first tools that a woodworker will purchase are a table saw, mitre saw, thickness planer or some other major power tool. These are all solid choices, but almost every project you build will require clamps of some type.
Commercially available clamps are found in a dizzying array of styles and prices. When buying clamps, if you are not familiar with the brand, have a look at the fit and finish. While it’s difficult to determine the quality of cast iron once it has been painted, there are still plenty of indicators to look for. To check the quality of the casting look to see if there are any rough areas ground smooth before the iron was painted. Make sure that any sections of multi-part castings are joined smoothly. Check to see that the jaw faces are perpendicular to the bar or pipe, and parallel to each other. Also, ensure that any screws move effortlessly and that the fixed jaws don’t slide when pressure is applied.
Generally, better quality clamps cost more. Individual clamps can cost anywhere from a couple of bucks to $75 or more, and a mid-size collection can easily cost as much as a major power tool.
Clamps generally fall into one of these categories: pipe, bar, parallel jaw, quick grip, fast action and specialty. If a glue joint is to achieve maximum strength then the clamping pressure must conform to the physical requirements of the joint, providing the correct amount of pressure in the appropriate direction with the correct amount of force. Each style of clamps has its own strengths and weaknesses and each is specifically designed to excel at certain tasks.
It is good practice to use some form of protection on your work piece when clamping. Most clamps can exert enough mechanical leverage to crush wood fibres if you apply too much pressure. You can buy face pads for most clamp styles, or you can make them for a fraction of the cost. My personal favourite is the thick cardboard edge protectors used to protect lumber when it is strapped for shipment. Hardboard is a good substitute, but any scrap of softwood will work in a pinch; just be sure to ease any sharp edges first.
By far the most common clamp for those working with solid wood is the pipe clamp. They come in two common sizes, 1⁄2″ and 3⁄4″, and range in price from $8 to $25, excluding the cost of the pipes. Not all pipe clamps are created equal. When you buy a pipe clamp, you receive a stationary end with a moveable jaw attached to a hand crank, and one moveable stop. These are fitted to a length of the appropriate sized pipe that must be purchased separately (available from most plumbing supply outlets). The fixed end of the clamp threads onto one end of the pipe, while the other end is free to slide along the length and is held in place by a clutch mechanism.
The jaws on pipe clamps are normally quite shallow, approximately 13⁄4″, but models with extra deep jaws are available from some manufacturers. The beauty of this system is that only the length of the pipe you choose limits the length of the clamp. Two shorter clamps can easily be connected with a rigid threaded coupling to make a larger one if the need arises. This type of clamp provides incredible clamping pressure for gluing up solid wood panels and for final assembly and gluing. When using long sections of pipe (around 4′ or longer), these clamps tend to flex. When purchasing pipe clamps there are several things to watch for. On cheaper sets, the faces of the jaws are not always square to the pipe and parallel to each other. When you apply pressure to glued surfaces they will have a tendency to want to slide past each other. On a wide panel with many clamps, this can lead to frustration and uneven panels. To allow the moveable end to slide on the pipe, a certain amount of play is required and this almost always results in the faces opening up a little. This will result in a cupped panel during a glue-up that can be controlled by placing clamps on both the top and bottom of the panel. On some clamps, depending on the pipe used and the design of the clutch, the live end will often shift as the clamp is tightened. One manufacturer, Irwin, has introduced a 3⁄4″ pipe clamp that doesn’t require a threaded end on the pipe. When clamping large surfaces, such as table tops, you can distribute clamping pressure more evenly by placing a caul (long narrow piece of solid wood) between the clamping pads and the edge of the work piece.
These are similar in nature to the pipe clamps, but they are a one-piece, ready-to-use unit. These come in lengths from 8″ to 8′. These clamps consist of one fixed and one moveable jaw mounted to a metal bar and they tend to be more expensive than pipe clamps. Within this category the cost and quality vary widely. In this group there are two distinct types, those with aluminum bars and those with steel bars.
Aluminum bars are much lighter than their steel cousins. This can be an important factor when gluing up smaller projects that might be pulled out of shape by heavier clamps or when you are assembling a large piece that must be moved. That weight saving comes at a price though. Aluminum bar clamps are much less rigid and will have a tendency to deflect when they are tightened.
Steel bar clamps are the heavy-duty version of this style of clamp. They allow the user to apply considerable force to the work without the clamp having a tendency to deflect. These clamps are so robust that it is easy to apply too much pressure, and excessive clamping pressure will result in the glue being forced out of the joint, resulting in a weak bond. Longer versions can be bulky and awkward to use in a small shop and if one of these accidentally connects with your project, a substantial gash or gouge is the usual result.
These are among the handiest clamps you can have in the shop. Similar in appearance and operation to the bar clamp, these have the advantage of being managed with one hand. This is of particular benefit when you are trying to assemble a large cabinet by yourself. Allowing you to hold your material in place with one hand while applying the clamp with the other is where these clamps truly shine. Used primarily for assembly and holding tasks, they don’t exert enough force for most gluing applications, and are usually replaced by other types during the glue-up stage. These clamps are also useful for holding large project pieces to a work surface while working on them.
Some clamp designs allow for one jaw to be reversed, allowing the clamp to be used as a spreader. This feature varies from one manufacturer to another.
These are also commonly called F-Clamps, and you’ll find a few of this type of clamp in almost every woodworking shop. They function on a principle similar to the regular bar clamp, but can be adjusted and applied with one hand, a useful feature if you work alone most of the time. There are two types of handles common on these clamps. The first is a long cylindrical wooden handle, and the second is a metal toggle that can swivel 90º to the screw.
For some users, the straight wooden handle can make it hard to apply adequate pressure, especially if they are affected by arthritis; the opposite is true of the toggle handle variety as the mechanical advantage the lever provides makes it easy to apply far more force than is necessary. The choice of handle is a matter of personal preference. These are affordably priced and come in a range of sizes from 12″ to 4′.
Developed less than 20 years ago, this is the newest kid on the clamping block. They take their name from the design – the jaws on this type of clamp are designed to remain parallel to each other as they are tightened. These have much taller jaws than the other types, maximizing the contact area, and they feature a greater degree of accuracy over their length. Because of their large jaw size and the fact that they are parallel to the clamping surface, you don’t need to use pads with this style of clamp.
When comparing the jaws of various clamps, these are consistently square to the bar, and parallel to each other. They are easily adjusted, although some might find that the smooth wooden handles make it harder to get a good grip. These are the most expensive group of clamps, and are also among the heaviest, second only to steel bar clamps.
Again, better quality comes at a price, but as a group, these are not very expensive. They come in sizes from 1″ to over 18″ and some manufacturers feature models with extra deep throats.
These clamps usually have some form of handle perpendicular to the screw, which allows the user to apply considerable force. Check the faces of the clamping surfaces as any imperfections there will be stamped into your project. When using this type of clamp on softwoods such as pine and cedar, it’s very easy to create a round depression in the wood with the screw end of this clamp. To avoid this, use pads for extra protection. These clamps are extremely useful when doing bent lamination work.
Not all assemblies and glue-ups are square and this has lead to the development of a range of specialty clamps. Band (or web) clamps, consisting of a long woven strap and a screw mechanism, are used to clamp large and irregular shaped objects. The clamps discussed in this article have largely replaced the old style wooden hand screw, but it is still a viable choice when clamping irregularly shaped objects.
Edge gluing clamps have a second screw at right angles to the main one and allow you to glue solid wood to an edge when you only have access to one edge and are unable to use standard bar or pipe clamps.
Holding two work pieces at 90º to each other is a job for a right angle, or corner clamp. These are available in light duty versions often used in picture frame work and heavier versions that can accommodate material up to 3″ thick that is useful for carcass work.
Spring clamps provide quick holding power when assembling components before you are able to get larger clamps in place. They resemble oversized clothes pins and can be had inexpensively from a wide variety of sources. Keep a selection of assorted sizes handy in the shop.
Coil spring clamps are very useful when gluing mitred edges, as they are able to provide solid holding power in a very small space. These small wire clips, made from spring steel are in the form of a ‘C’, and are from 1⁄8″ to 3⁄16″ thick. They are opened with a tool resembling a pair of pliers, with the ends placed over a mitred corner and the pressure released. This holds the joint in place, but they can leave small divots in the material. These usually come as a kit and are rather expensive.
Toggle clamps are the ideal clamping solution for shop made jigs. They offer great clamping pressure in a small package and will clamp downward or horizontally (inline). These are typically not used in gluing situations except in production type jigs.
Wooden cam clamps are very popular with instrument and model makers. They are light, adjust very easily and have non-marring cork lined jaws.