Shields on Precision Woodworking

Precision Craftsmanship applied to the Art of the Lamp

Trying to achieve precision with woodworking is a huge challenge. Being a natural material, wood wants to do it’s own thing. It’s hard to take something that grew in random organic directions and try to make it into a piece that is flat, straight and stable. This is a constant effort to overcome. Wood will shift or move due to environmental conditions and random pieces can break off or chip away unexpectedly no matter how careful cuts are made. To achieve precision in my joinery I apply techniques and take extra time at each step to increase accuracy so that minute errors do not compound and cause visible defects. I’m always trying to find better tools or ways of doing things including looking outside woodworking. Many techniques are the tried and true habits of fine craftsmanship used through out the ages, others are ones I have adapted or thought up as my skills have increased. My goal here is to pass along a little of what I’ve learned so far.

Start with dry, stable wood! Get a moisture meter. They can be pretty expensive, easily in the hundreds of dollars. But I got a decent one (contractor grade) for about $65 or so and it works pretty well. It has both pins and a sensor pad (pinless) but I always use the pins. The goal is to get the right moisture content for your project. If you are doing carving, air dried wood at about 12% moisture is fine. But when building fine furniture, the wood should be carefully brought down to 5 or 6%. At that point the cells in the wood tend to close tightly and are much more resistant to re-absorbing moisture. This is according to the 50 pound heads at some University somewhere that studies this stuff. The wood can still absorb moisture just not as fast, so by keeping the wood in a controlled environment while you are working it then use a good film finish that seals the wood it tends to get a lot less movement or shifting over time. I mill a lot of my own wood then stack it to air dry for a year or so, then put it into my solar kiln. Solar kilns are easy to build and there are hundreds of designs on the internet. I took what I thought were some the best ideas and designed my own, it breaks down into 7 flat panels that can be loaded on to a truck. The kiln gently brings the moisture down to where I want it then I move it into my shop (climate controlled) for storage. Be careful though! you can dry below 5% and all you have is expensive fire wood. When I buy lumber, it has obviously been dried in a high temp commercial kiln but spends a lot of it’s time stored outdoors until I take it home. I always like to store it in my shop for a few weeks before I use it to help it acclimate much like you would with hardwood flooring.

Accurate measurements are key! I use very accurate measuring tools in my everyday work. Thankfully really fine measuring tools for woodworking are becoming much more common but sometimes you need to adapt tools from other disciplines. For example, when I plane my boards, I measure the thickness with my dial caliper like a machinist. As I start to get close to final thickness, I take measurements at several places along the piece after every pass, using a simple ruler or tape measure here wouldn’t be accurate enough. When I’m making 3/4” stock (the usual thickness for my projects), I very carefully plane the boards to .752”, this will give me a few thousands to finish sand down to a true .750”. When these parts are used to fit into a slot or joint I hand sand them so they just barely slip into place. In my case, the precision is critical because my designs have very distinct and complex angles. If a piece gets planed below .749” (usually to correct a blemish in the wood), I will use it for a flat base or another part that is not a fitted joint. Visually you can’t see the few thousands difference plus nothing goes to waste. Every woodworker should learn to use a dial caliper, they have many uses and are very accurate. They can measure inside, outside, step and depth measurements easily. Vernier calipers and digital calipers work too, but for my aging eyes, the dial caliper is the easiest to read and doesn’t need batteries like my digital does.

Other essential measuring tools that get used constantly are really accurate rulers, straight edges and squares (more on squares later). My favorite ruler is from Woodpeckers, it has a “Standard” scale on one edge and a “Center” scale on the other. I had never used a center scale before I bought this ruler, and now I use it almost daily. Simply put, it is a scale with “0” in the center and the graduations going out both left and right. It allows you to accurately and quickly find the center of a piece by getting the 0 near the middle and then fine tuning the the graduations so they are exactly the same on both edges, then the 0 is perfectly centered. It is a lot easier than measuring the width of something then doing the math. I use center marks and center lines a lot, they are great for assembly processes as well as joint lay outs and a hundred other things. Different sized pieces can be perfectly aligned using center lines instead of trying to match the offset on outer edges. The other tool that is a necessity is a good straight edge, it has a bunch of uses but a good stiff thick one is best at checking for flatness on many surfaces.

Get on the slab! Squareness is essential to very tight joinery and must be checked constantly throughout the process. Sometimes a very minute discrepancy that goes unseen will cause major problems 2 or 3 steps further along during assembly. My main assembly station is a thick slab of granite, this is a great technique I’ve learned from machinists. Polished granite can be flatter than glass so I use it to accurately measure and then fit my parts. You have to check the slabs though, I have found that regular “counter top” granite or marble pieces can have a slight sag in the middle or other unevenness, so you need to make sure to check it with your straight edge. The real deal is a machinist granite “surface plate”, these are seriously expensive but many are accurate down to .00005”. These obviously are overkill for wood working but if you run across one at an auction or estate sale and can load it in your truck (they can weigh 400 to 600 lbs!), then grab it. They are great for checking flatness and sanding a fine edge on tools.

I use my slab work station to glue up parts or sub-assemblies in order to get the truest fit. What little glue that sticks to it, scrapes off with a razor blade after the parts are done. If you want a part perfectly straight, glue it up clamped down to some granite. The granite slab is also perfect for sanding something really flat. I often have sandpaper taped down on one end of my slab so I can carefully work the parts flat in preparation for assembly. This works great for smaller parts because you are moving the part and not the paper but the paper or granite are only so big. My slab is about 32 x 22 inches, good size for me, but you could get a larger piece of granite for bigger projects. I have a big piece, it was a large counter top from a restaurant, it was given to me when they did a remodel on the place but I haven’t checked it for trueness yet. They said all I had to do was take it home! What a job that was, the math says it’s about 350 lbs., but it felt like a ton. It’s waiting patiently outside my shop, quietly altering the rotation earth due to it’s gravitational force. I’ll have to build a serious work bench to hold it, all my benches are serious but this one will have to be next level. It would be like setting a small block V8 on your work bench and then pushing it around as you work hoping the work bench won’t fold up underneath it. Yeah……

Get the best square you can find! I hate to say it, but most squares aren’t square. I broke down and bought a steel machinist “check” square some time ago. It was made in Europe and came with a signed and stamped certificate stating that it was accurate down to 0.0007. It is also made out of very heavy bar stock over 1/4 inch thick so I’m not likely to bend it, surprisingly it was not very expensive. If you want to get humbled, use a machinists square on a granite slab to check your work. A while back, I had a part that I could not get right no matter how hard I worked it and I was getting very frustrated. I happened to use my machinist square to check one of the corners and found that it was off. Surprised, I checked my expensive and highly accurate lay out square (which I had been using on the part) with the machinist square and found it was off! Apparently it had been dropped, just days before, when we were moving into our new shop. It was bent but you couldn’t see it, however the machinist square told the story. I sent the square back to the manufacturer to see if it could be fixed, they tested it and promptly replaced it even though I had damaged it. Great people! A good machinists square is a must, they’re not too expensive, and you can use it to check your work, and also to check your other tools. I have taken it to the box store (to test with) to buy an inexpensive square for general carpentry projects and had to go through about 10 off the shelf squares to get one that was “close” to square, no kidding. A machinists test square is also great for your machine set ups, but they don’t normally have any graduations on them so you will still need a good layout square.

Every once in a while I’ll come across a new technique or tool that’s a game changer, it’s great to see there are other minds out there working the problem. One of my favorite companies is Woodpeckers, they are always coming up new innovative ways to increase accuracy and I have several of their tools in my shop that I use daily.

The plan is to add to this page as things come along so be sure to check back.