Repeatable Accuracy
Accuracy is how close you come to the value you are attempting to achieve. In woodworking, that’s often cutting a board to a specific length. A simple activity that is tougher than it seems.
A beginner wanting to cut 4 table legs all exactly 28 inches will break out a measuring tape and pencil, hook the tape on one end, mark a line where the tape says 28, and make a cut right there. They will then repeat this process three more times and expect to have 4 boards all exactly 28 inches long. They will stack those boards, sliding the ends together, and realize they made 4 boards all near 28 inches. One was 28 1/8, another 27 15/16. Depending on the tables use, this may be acceptable, but only if the user is okay with using a stack of napkins to prop up one leg so it doesn’t wobble.
Enter the intermediate woodworker. They have learned the beginner’s lesson and found a way to overcome it. Starting the same way, a tape measure and pencil comes out of the drawer. A mark is made at 28 inches and the board is cut. Then, that board is used as the measuring stick for the remaining 3 cuts. The original board is placed on the stock and lined up at the end and edges. A mark is made and that line is carefully cut to, just removing the pencil. And each board comes out better, within a 32nd, an acceptable cut for most cases. But consider that one board is under 28 by a 32nd of an inch and another is over by the same amount. That compounds to a full 16th off. That doesn’t seem like much, but a 16th inch gap in a stretcher is huge. It pulls the other legs out of square, causing things to turn, leaving the table wobbly, just not as bad as the beginners.
Now the advanced woodworker comes in. They have the same task but start in a different spot. They go directly to the saw and setup a stop block at 28 inches. Then they grab a scrap piece of wood and use that stop block to make a test cut. They check to see that it’s on using a rule, not a tape, and adjust accordingly. Once everything is tuned in they quickly make all the cuts and end up with 4 identical boards. The advanced woodworker did something the other two did not, they removed the human error element.
The difference here is the first two relied on their least reliable sense, their sight. The advanced woodworker knew they could not make a consistently accurate mark based on a tape measure, so they eliminated the need for it. Accuracy must be repeatable, and the only way to make it repeatable is to use tools that are built for repeatability. Here are a few of my favorites.
Repeatable, accurate, these tools are all designed to take a measurement and hold onto it so you don’t have to. From the top down, Combination Square, Calipers (2), and Marking Gauge. The angled one is a Bevel Gauge.
Combination Squares
One of my favorite tools, a combination square. It can be used to measure, to mark, to check for square, to check for 45, check for flat, and draw a straight line. I purchased this inexpensive tool years ago from a big orange store and it has served me well. For years I used this in place of a marking gauge because it can function the same way, with two hands instead of one.
The combination square is a rule that sits in a body with two angles. One 90 degrees to the rule and the other 45. The rule slides back and forth so you can use both sides and to set a distance from the face of the body. I use mine for all sorts of things such as checking the depth of a dado, setting the distance for a cut such as a tenon, and as a typical square to draw perpendicular lines from an edge. These squares work great because they can be adjusted, creating a stop that can be used to set the same distance over and over on multiple parts, ensuring every single one of them is the same, no measuring needed.
Marking Gauges
A marking gauge sets a distance from an edge by severing the wood fibers. By severing the fibers, you do three things. Set a fine line, much finer than any pencil can. That line then creates a stop your tool can feel, blade will want to follow that new line rather than divert with the grain. Lastly, by severing the wood fibers you create a weak spot which will break cleanly and evenly, stopping tear out in it’s tracks.
You don’t need a marking gauge. I got by for years with a combination square and knife, but eventually got a marking gauge because I wanted to increase my efficiency. A marking gauge can be used with one hand, freeing the other hand for holding the stock steady. A combination square and knife combo rely on two hands holding two tools and the work piece to be clamped, a slightly slower process per mark, but those per marks add up quickly.
Secondly, it’s always good to have more than one type of these tools. That goes for calipers, combination squares, and marking gauges which all do roughly the same thing. They take a measurement and hold on to it for future reference. It’s extremely important to hold on to those measurements in case you need to go back and use them again. Having one tool to hold your measurement means changing and going back is introducing error of the eye.
Calipers
I’ll admit, I’m not the biggest caliper user, so I won’t spend too much time on them. As mentioned, calipers can take a measurement and hold on to it. The nice thing is they can do it three ways, the outside of an object, the inside of an object (such as a hole or mortise), and the depth of an object (such as a hole or mortise). Useful when you have a mortise cut and want to know how long to make a tenon. I also use them to check the thickness of stock and measuring different areas to find inconsistencies.
Bevel Gauge
A less important tool early in your woodworking. You will be focused first on straight lines and 90 degree connections. Eventually you’ll branch into miters, which can be measured with your combination square. The next progression is to use other angles. That’s where the bevel gauge excels. You can set an angle and keep it with the gauge, giving you the ability to transfer that angle to other pieces and parts or even tools. The best part, you don’t have to worry about what the angle is, eliminating all math. Just make sure it looks good.
Stop Blocks
Stop blocks allow for consistent cuts, period. If you need 20 identical parts, use a stop block and you’ll have 20 of the exact same size. Useful at the miter saw, table saw cross cut sled, router table, and other tools I’m probably forgetting. They are a physical way to know where to put a piece of wood so every single time you cut, the end is equal distance from the blade. If you want to know more about stop blocks I wrote a whole article about them called, Improving Consistency with Stop Blocks.
Templates
A template is a pattern. A piece of wood which has received all the shaping and planning for a piece which can be traced, cut, template routed, and used again over and over to make as many of the exact same versions of the part as you need. Have you ever heard of the concept, economies of scale? The concept is simple. As a business gets bigger and does more of a thing, they can do it faster and for cheaper. Templates are your economies of scale. They allow you to do things faster and more consistently. It’s how furniture shops make the same piece of furniture over and over and have it look the same every time.
Jigs
A jig can be complicated or simple. They can be homemade or bought. But they all do one thing, make a task repeatable and safe.
A tapering jig for table legs made from scrap plywood and 2x4 offcuts. Jigs don’t need to look fancy. Use what you have and they’ll get the job done.
A simple example is a straight guide for a circular saw. The beginner way to cut a straight line with a circular saw is to clamp down a level and make the cut. The intermediate woodworker will make a jig consisting of a sheet with a straight edge adhered to it. The blade lines up perfectly with the edge of the sheet and takes away all the measuring, making the operation faster and more accurate. The pro will go buy a track saw which is the same as the intermediate woodworker’s jig, but they didn’t have to spend time making it and the metal track can stand more abuse before needing to be replaced.
Jigs can also be complicated. Recently, I needed to cut a taper on some legs and I came up with the pictured jig. It was a bit overly complex, but I wanted consistent tapers in all four legs with the potential to make more of these tables. Pro tip, write down what the jig is for and what size wood needs to go into the jig to make it work. But most of all, I made this jig because I did not have a safe way to make this cut without it. With the jig the work piece is secure, the offcut has a place to go, and my fingers are out of harms way.
The jig in action. A leg sits in the cradle, the arm pivots to hold the workpiece in place and is locked down by tightening the screw. Then the jig is simply slid through the saw allowing the offcut to fall safely to the side of the blade.
Repeatability
The take away is to take yourself away, remove the error prone being and let the tools do the work. Your marking gauge, once set, will not lie. Your stop block cannot cut a different length board. Templates and jigs make work repeatable, increasing accuracy, advancing your work from amateur to professional.