Accuracy and precision: what is enough?

I asked this question a while ago on a forum I frequent. It generated a lot of discussion and exposed tectonic faults in the community. There seem to be two camps. One says "it's wood, it moves, don't worry about it" and the other seems to say more precision is better. There of course are diminishing returns when we are talking about wood because of it's "plastic" nature but it's also true that this is more about perception than anything else.

Before I delve into the heart of this, I want to share an experience I had. In making a 3/8" finger box joint, I used a straight 3/8" bit. The bit was inserted into router collet well past the "min insert" line so I assumed this was good enough. I proceeded to cut the fingers and much to my surprise the joint was very loose and the gaps between fingers were really obvious. Every thing else was uniform. The fingers were about 10 mils (0.01") too narrow and the slots were the same amount too wide. Some one I know suggested runout on the bit so I went back and looked at it. I pushed the bit all the way into the collet and then backed it out about 1/16" (like I knew I was supposed to all along). Then, I cut a new set of fingers. Lo and behold the joint was tight. The lesson here is that incredible tiny errors can make a huge difference. OK, the other lesson is push your bit into the collet as far as you can (minus a tiny amount) and ignore the min insert line which is really about router safety.

My contention is that accuracy is important but how your piece is perceived is the crucial factor. Take two different butt joints. One where both pieces are a light colored wood like maple and the other with contrasting woods, say maple and walnut. No matter how tight you clamp there there will be a visible line with some small gap where the two surfaces meet. Almost any gap in the all maple joint will be obvious but the same gap in the maple and walnut joint will be much harder to see. Also, the eye is good at detecting uniformity; a gap that is even a hair wider at one end will be obvious. So, to me the consistency of the joint is as important as it being tight.

Another factor that I feel important is that instead of cutting a part to a specific predefined measurement we should be cutting to fit the existing situation. This is what old timers often mean when they say "sneak up on the cut" but there are other examples. Take the exact width dado jig. There is no measurement taken other than using the end of the board that will go in the dado to set up the jig. This allows for a precise fit based on the actual piece but no measurements were taken and transcribed. A kerf maker is another example of this kind of thinking. Avoiding numbers is a big win in these situations.

I've been a woodworker most of my life but only got serious about quality in the past few years. I'd always been a little frustrated about being stuck in a middle gear when it comes to my level of quality. To raise it. I spent time reading and asking questions and generally thinking about how to become more consistent. To this end, I started do a number of things: cleaning dust between cuts, scribing cut lines, light sanding cuts between operations, paying attention to consistent pressure when feeding through saws, regularly tuning up my tools and so on. This has really helped and I feel like I've reached a much higher level of quality. The reason is fairly clear to me. By cleaning, sanding, using even pressure, I reduce the amount of error in my operations. These are, indeed, small errors. Does a little sawdust contribute even 1/64" of an error? Does changing the place where I hold the wood against the miter gauge matter that much? In isolation, perhaps not but errors compound and, as my router bit example above shows, it doesn't take very much.

So, in my thinking, it's not numeric accuracy or precision that leads to better quality but rather consistency and care in woodworking operations.