Thread: Darkside v electron burning - a question of precision versus accuracy?

Late last night I was working on the doll's cradle that I am making for my daughter's third birthday (only have two weeks to go and, of course, I'm running late).

I had originally been going to use some quick and easy half lap joints. Then I thought that some more intricate joinery would look nice and started planning it.

Once I got the joinery idea clear in my head, I started to try to work out what combination of tools I was going to use to make the joints. Halfway through that process, I realised that most of this was going to be a "darkside" job.

The reason was that most of the materials have been reclaimed and are not standard sizes. So every trench or groove that I make, if I make it with a router, will need two passes at least and that will mean some quite intricate setting of guides and fences, especially as most of the pieces aren't rectangular! The fact is that, by the time I mark it out and set up the guides and fences, I will in all likelihood have completed the job by hand, even though the woods I'm using it are really hard (Sydney blue gum and spotted gum).

This leads me to wonder whether the difference between precision and accuracy.

There is no doubt that modern power tools often make it possible to treat wood like metal and plastic - a material that can be precisely dimensioned. It is possible to do that by darkside methods as well. However for me once I have a piece that is flat and smooth and that looks about the right size, then the difference between, say, 20 mm, 19 mm and 17.7253 mm is irrelevant. The joinery will accommodate that material and the material will itself be used (using dividers wore calipers) to provide the relevant dimensions for the joinery rather than a tape measure or a micrometer. The joinery will be accurate in (often, in my case, more accurate) because there is no expected dimension to be produced but only the dimension of the rebate, groove or pin or tail or whatever that is needed to make an accurate piece of joinery.

This explains to me why I use chisels and planes and handsaws when I'm working in "real" wood that I dimension myself and routers and table saws when I use man-made timber (chipboard, masonite, MDF, blockboard) that itself is precisely dimensioned. If you have 19 mm blockboard, for example, your 19 mm router bit will produce a perfect trench - not only will it be precisely 19 mm but it will accurately accommodate your 19 mm blockboard. In that case precision gives rise to accuracy.

If, however, your hand-dimensioned timber comes out at 37/64" then you use that timber,rather than a tape measure, and things that reflect that timber to lay out the joinery and it is usually easier to use hand tools to get the required joints to fit. Those joints will have completely irrational dimensions but they will fit together accurately.