No Math

It’s always nice when you can see¹ a project from the train:

We’ve worked on a lot of mid-to-late-1800s churches and there are a few rules of thumb that are almost always helpful. The roof trusses, as originally built, will have members that are big enough, but may have problems with the connections. The masonry walls, as originally built, are oversized for their loads. And the spires, as originally built, defy easy analysis. Here’s a couple of Ellen’s pictures looking up into that scaffolded spire:

A few things should jump out at you. There are wood members running in a lot of different directions: ribs that are “vertical” along the spire corners, horizontals and diagonals connecting the ribs on the outside faces of the spire, and horizontals and diagonals connecting ribs across the interior space. Some of those connections are pretty sketchy: toe nails, or unpegged mortise and tenons.

Trying to map it all out on drawings is difficult, even if drawn in 3D CAD: things aren’t necessarily symmetrical, and the centerlines of members don’t necessarily meet at points at the connections. And here’s the fun part: the carpenters who built this didn’t have drawings showing where each piece went, and didn’t calculate the length and angles of the pieces.

There are all sorts of ways to mark wood for cutting to fit without doing the math – trigonometry, generally – necessary to calculate the geometry. I suspect all of those tricks were used when it came to building a spire.

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1. All pictures are Ellen’s, as it’s her project. ↩︎