GEOMETRY: MISFITS AND DISTORTIONS

GEOMETRY

MISFITS AND DISTORTIONS

“All lumber should be cut to exact dimension and straight without warp, twist, wane, or split. Walls and columns should be exactly vertical. Floors should be perfectly flat and level. Foundations should be at the precise elevation, absolutely straight and level. Stairs and roofs should have exact slope or pitch. Joists and studs should be uniformly spaced and perfectly parallel. Door frames and corners should be square to within an arc-second. Trusses should be straight as a fiddle string. Square and bevel cuts should be right-on and straight clear through. All joints should fit snuggly without gaps or warping. All connections should join evenly for a smooth surface”.

Sadly, the above ideals cannot be achieved in this sinful world even individually, let alone all together! A skilled carpenter knows how to remedy flaws and recover from errors, without resorting to “Cut to fit, warp to connect, grind to bear, and paint to match” – hopefully this common solution will be used sparingly. A wise worker also pays attention to manufacturers recommendations when installing fixtures, etc. The common solution of “using a bigger hammer” to make things fit should be avoided!

Distortions from the desired geometry can be due to many factors. Sections built off-site have to be transported, which can stress and alter their shape. Tall, narrow sections are difficult to build true to square and parallelism. Wood changes dimension across grain, (but is stable along grain) and it warps and twists. Concrete cannot be placed absolutely flat. Plumb and level is hard to verify over long distance with only a spirit level.

Spirit levels, tapes, and string lines are the usual tools we use to layout, control, and check the geometry and construction. Optical and laser instruments are now found on many projects, and can provide greater accuracy. Unfortunately, these tools are often misused, their relative accuracy or reliability not understood, and the relative importance of geometrical elements is frequently not recognized. When things don’t fit right, what should give: line, grade, level, plumb, straight, flat, smooth, parallel, square, spacing, pitch, or dimension?

The best answer to this question will vary depending on several factors. Some things are critical, others of minor importance. There is distinction between what should be nearly perfect vs. what can be barely adequate. Is the defect potentially dangerous, just ugly, or merely annoying? What crooked piece is the likely cause of the trouble? What reference line or measurement mark is most susceptible of error or mistake in determination and therefore most suspicious?

Some parts that are especially critical are door posts, wall corners, and joists and studs to which sheathing is attached. Interior “non-edge” misaligned studs can be tolerated, providing they are securely blocked. Some things that are out of level, plumb, or square, may be tolerable if they are to be covered, are not critical structurally, and providing the defect is not too egregious.

It’s probably safe to say that most misfits occur because of defective measuring, sloppy marking and cutting, and careless fastening, abetted by warped lumber.