Woodworking is an intricate process that uses various tools and processes. While working on wood, sometimes things don’t go as planned. One of the issues that can adversely affect your work is racking.
What is racking and how can you prevent it? Racking occurs when the workpiece shifts while working on it, causing vibration. It can hamper your work. It can also occur in furniture if not assembled properly. If you know why racking occurs, you can prevent it by taking some basic precautions like using vises and clamps correctly.
Racking is a common problem that occurs when you clamp your workpiece in a woodworking vise. It can be due to the incorrect design or structure of your tool. The main reason for racking is uneven pressure exerted by the jaws of a vise.
You will see racking on your workpiece if the sliding jaw of your vise isn’t parallel to the fixed jaw. It can also happen when you clamp an object at one end of your vise, but you have nothing at the other end to support it.
The result is that your workpiece rests unevenly with both jaws at an angle, causing uneven pressure on it. The workpiece will slide or vibrate when you start working on it.
Types of Racking
The two types of racking you can observe in woodworking are top-to-bottom racking and side-to-side racking.
If you position your workpiece on the top part of the jaws of the vise, top-to-bottom racking can occur. Here, the sliding jaw of the vise moves away from the workpiece at the top part. The workpiece remains held at the bottom part.
As you apply force to your workpiece while cutting, drilling, hammering, or machining it, the workpiece moves. It will start to slide or vibrate in the jaws. The reason for this occurring is that the guide mechanism and the thread of the vise exist on the bottom of the device. Due to this, the workpiece gets insufficient support at the top.
You will most likely experience top-to-bottom racking with a plain screw and quick-release vise, owing to the structure of the tool. This can be remedied by including a toe-in feature. You get these already installed in some vises, or you can add them by including a tapered jaw pad.
Side-to-side racking is a result of clamping the workpiece on one side of the jaws of the vise. The lack of support on the opposite side of the vise jaws creates an imbalance. The uneven force results in the workpiece being insufficiently held.
In such a scenario, when you apply force on the workpiece while working on it, vibration or shifting may occur. You will see side-to-side racking occurring with face workbench vises. It happens due to the rather wide jaw design of this type of vise.
Causes of Racking
We touched upon the types of racking and why they occur above. Let’s look further into detail about why racking occurs:
To clamp an object satisfactorily, it needs to sit squarely between the jaws of the clamp. If not, the object becomes misaligned and when you tighten the jaws, racking occurs.
If your workpiece moves whenever you touch it, you will find it difficult to saw, plane, sand, or perform any action on it. Depending on the shape and size of your wooden workpiece, there are various ways of securing it.
A common fix to prevent racking with uneven clamping from a bench vise is to insert two rectangular pads of wood between the jaws. It usually suffices to hold the workpiece firmly enough in the vise to work on it without racking.
If you place a workpiece too much on one side of a vise, the clamp becomes uneven. The side of the jaws with no wood receives less force than the side holding the workpiece. The workpiece tends to act like a pivot. The more you tighten the vise, the more unstable it becomes between the vise jaws.
Whether you use a small or big vise doesn’t matter. If you place your workpiece too much to the side in a vise, it results in racking. The instability of the workpiece is similar to being unevenly clamped.
A common type of clamping in woodworking is when you join sections of bookcases or cabinets that need to be glued together. If you apply clamps incorrectly, racking can occur.
The result is that the sections may be out-of-square and remain so even after the glue dries and the clamps are removed. We usually prevent this type of racking from occurring by adding diagonal braces.
Racking can occur in furniture from various types of external forces being applied to furniture. If the joints on a table for instance, are not strong, racking can occur if people lean against it. This type of racking, if applied to furniture can make the joints become loose and end up damaging the furniture.
How to Prevent Racking
Once you know about racking and its possible causes, you can take measures to prevent it from happening. Here are a few best practices to prevent racking:
Install diagonal braces on your workbench legs. The braces should extend from the bottom of each leg to just beneath the tabletop. For maximum reinforcement, you should install the braces on both sides and in opposite directions.
Having your workbench legs reinforced by braces can add additional stability to it. You will find this particularly useful while applying excessive force to your workbench like during planing operations.
Use a Vise Correctly
The best way of preventing racking from occurring is to clamp your workpiece in the center of the vise or clamp jaws. By doing this, you apply even pressure on the workpiece from the jaws of the vise or clamp.
Sometimes it isn’t possible to clamp the workpiece in the center of the jaws. With long jaws, you can add a dummy workpiece at the opposite end. It would be a piece of wood roughly the same thickness as the workpiece.
Also, ensure to apply just enough force to hold your workpiece firmly in a vise. If you don’t clamp it tightly enough the workpiece will become loose and racking will occur. If you apply excess force, you stand a chance of marking or even damaging the workpiece.
Checking for Squareness
When we assemble long sections of wood, we generally want them to be square, meaning that they should be perpendicular to each other. If the clamping is out of sync, racking can occur.
Typically, you will apply clamps or put a workpiece in a vise after applying glue. The sections need to be square while tightening the clamps. You can ensure squareness by adding backing boards or bracing.
Some furniture features bracing that seems to be cosmetic but also doubles up as reinforcement to prevent racking. Before you complete the final tightening operation of your clamps or vise, check for squareness with a square.
Racking is something that occurs at all stages of woodworking. From roughly planing the wood to the final assembly of your project, racking can occur. If not checked, it can be detrimental to the final results of your project.
Here, we have explained what racking is, why it happens, and how to prevent it. You can use this information to make your work easier and more accurate in your next woodworking project.