It was an exciting day, almost like Christmas in the middle of the summer. Dad came home with a new Sunbeam electric lawnmower. The old one was pretty tired and worn out which prompted the purchase of the shiny new blue beast. Some assembly was required to attach the handle, so Dad brought it into the living room. I don't remember whose idea it was to make sure it worked, but someone (probably my older brother Ken) plugged it in and flipped the switch. There was a woosh and suctioning sound as the mulching blade grabbed the braided rug and started to digest it from the middle out. It was impressive and awe-inspiring. Lesson learned — Never Start Outdoor Power Tools in the House. Here we are 50 years later, and I am sure Ken thought about this as he took delivery of his new snowblower, "Probably shouldn't check this out in the living room."

Figure 1 - The Rug Eater.

We learn as we go through life. There are the facts-and-figures kind of knowledge that we acquire — "The Stanley bench plane was originally designed by Leonard Bailey in 1867" or "The threads on a saw arbor are left-handed." There is a lot of that kind of explicit (also called "knowing what") knowledge to pick up as you develop as a woodworker. But there is a deeper knowledge that we acquire through experience called implicit or tacit knowledge ("knowing why"). Tacit knowledge is what is absorbed into your being through experience in a way that makes it instinctive. You don't consciously think about tipping the pencil away from the straightedge, but you have absorbed the lesson that accurate marking matters and you have developed a habit to keep the pencil at the proper angle for a more accurate line.

One of my earliest lessons in the shop is marked by a thin white line across the back of my left thumb. I was holding down a piece of wood with my left hand while I cut out a part with a coping saw. In a split second the board broke and the downstroke of the saw pulled 4" of sharp teeth across my thumb. I am sure it was stopped by the bone. From that one experience when I was very young, I am generally very aware of where my hands are in relation to the cutting tool. Through pain and injury, I learned to appreciate the value of good workholding devices. They say, "Experience is a hard teacher because she gives the test first and the lesson afterwards." Experience is also the best teacher. Once was enough.

Figure 2 - Danger Will Robinson!!!! Move your hand away from the line of the cut!

Tacit knowledge becomes a part of our being when we generalize the lesson learned to a mental model of how the world works (truly understanding "why"). My junior high shop teacher did a really good job of impressing us with tool safety. "See that hole in the concrete block wall? That was a kickback from the tablesaw. Avoid kickback." That lesson is explicit knowledge — remember this single fact — avoid kickback. But when you grow beyond the fact and think about how kickback occurs, the forces involved, and proper procedures, the whole concept of saw kickback becomes part of your tacit knowledge of working with a tablesaw. You develop a clear mental model of how saws and boards work. When I rip a board there are lots of things running through my head like watching the cut to see if internal stresses in the board are closing the cut. Feeling the resistance of the saw. If I were to tell you what to do, I would say, "Rip the board". But it would be hard for me to detail all the things that I am processing as I do it safely and confidently. That's tacit knowledge.

I was recently assembling a piece of mid-century furniture that used doweled joints. Grabbing my doweling jig I quickly marked out and drilled the holes. I checked that things lined up (remember that time the jig slipped, and the boards didn't line up correctly?). Check. Next came the glue and the factory-made dowel pins and the clamps. Looking good — until the last 1/32". For the life of me I could not get the joint to pull closed no matter how much I torqued the clamps. And then I remembered that I hadn't gauged the depth of the holes against the new package of dowel pins. The kicker is that I did the exact same thing on a kitchen cabinet build a while back. Will I learn the lesson this time? Or am I going to have to repeat this class again? I know the facts about dowel joints and dry assembly procedures, but I haven't quite completely absorbed the habit of dry assembly into tacit knowledge.


Growing your knowledge is a lifelong process. Sometimes when you think you know everything, life has a way of giving you another lesson. Years back I was helping my son make a jewelry box for his girlfriend. Wanting to use some contrasting light wood for accents, we found a piece of magnolia in the firewood pile and ripped out some thin boards. I have a degree in Forest Products, so I knew about kiln drying. But we needed to get this wood dry right now and kiln schedules don't go down to 4 hours. I also distinctly remembered a random fact from high school — the ignition temperature of paper is 451° F (the title of a Ray Bradbury book). If we kept the kitchen oven under 400°, we would be safe. With the timer set for 2 hours we headed back to the shop to work on other parts of the box. It is amazing how much smoke a few small boards can generate in the early stages of pyrolysis (between 212°F and 400°F). My wife, Jean, returned home about the same time Steven and I came up from the shop. On the plus side we had been meaning to replace the drapes and repaint the living room anyway. My mental model of wood drying was deficient, and I was led astray by thinking I knew more than I did. Humility is always a good thing.

Figure 4 - Are you ready to repaint the living room?

Some of the research on learning and tacit knowledge points out that learning changes us both physically and mentally. When you learn to play a musical instrument, for example, your muscles and nerves and brain get rewired to subconsciously connect hearing and fingering and your heart to be able to perform a beautiful piece of music. The concertmaster isn't thinking about where to put his fingers on the instrument, he is making music and his whole being is engaged in the activity. As we develop as woodworkers and grow our tacit knowledge, we change. We instinctively position a tool for the right slicing cut, we feel the texture of the piece and know when to change to the next grit of sandpaper, we can sense when something isn't working correctly. Mind, muscles, nerves, senses, and heart - our whole being is engaged in shaping and working wood. The deepest joy of woodworking is when we are free to make, to simply focus on the realization of design come to life through our hands.

Bob Rummer lives in Colorado and is a part-time woodworker. He can be reached directly via email at rummersohne@gmail.com. You can see his shop and some of his work at www.JRummerSons.com.

Return to the Wood News Online front page