Sunday, August 9, 2009

A Cut Above

Saturday I spent all day helping Ma'ikwe build her house. She has seven close friends from her Albuquerque days (2003-2008) visiting this week, and it was fun being part of the menagerie for a day.

It was essentially a three-ring circus, with occasional side shows. One locus of worker bees installed purlins over the northeast quadrant of the roof, one mounted rafters over the northwest quadrant, and the third prepared meals and kept the cold drinks coming (it was hot and windy all day).

While there were no assignments ahead of time, and people were more or less free to work where they wanted (excepting who'd cook each meal), I wound up assisting on the rafter crew, doing one of my favorite jobs—cutting boards to exact specifications. As a 59-year-old, I leave the rafter dancing & hammer pounding to those with younger legs and more practiced arms.

My tools were a circular saw, a straight edge, a carpenter's pencil, a tape measure, a speed square, and a hand saw. Simple as this tool set was, there are a number of nuances about using each element well, and I got considerable satisfaction out of dusting off old knowledge and harnessing my hands and head to contribute even in a small way to my wife's house.

1. Carpenter's Pencil
These construction oddities are soft lead encased in a distinctly ob
long wooden shell. On site, where few surfaces are level, they simply won't roll. They'll stay where you put them. You can easily sharpen them with a utility knife. The trick to getting a clean line is to resharpen frequently and to hold the pencil at the same angle every time. In general, it works well to try to replicate the angle at which you've sharpened the point when you hold the pencil against your straight edge.

2. Straight Edge
As the rafter wood we were working with was recycled 2x12s, I needed a straight edge to extend the lines I'd mark out with a speed square (while they make a larger version, ours was the standard size with sides only a hair longer than six inches). While I could have used a framing square instead of the speed square/straight edge combo, the speed square is such a quick layout tool that it was preferable to use two tools. In this case, I chose a two-foot level. It was light and plenty long enough for my purposes. The trick was being diligent about how far away from my line to hold the level (about 1/8-inch is usually right) and then using a constant angle when marking with the pencil.

3. Speed Square
First invented in 1925 by a carpenter named Swanson, this cast aluminum tool is a workhorse on a construction site. In addition to making layout of perdendicular cuts a snap, it's the perfect tool for laying out bird's mouth rafter cuts. These are the angled bites of wood taken out of the bottom of each rafter such that they rest flat on the beam (or top plate). There's one at each end. Once you know the angle at which the rafters lay, it's simple
using the speed square to replicate the exact same cut, board after board.

4. Tape Measure
As all the lumber for the house has been recycled, there's considerable variation in dimensions. While they were all nominally 2x12s, some were nearer to 11" wide and some were proud of 13". Some were 1-1/2" thick; others a hair over 2". The tape, or course, is used constantly to measure these variables, and to determine the exact location of the gap between bird's mouths—so each rafter will fit snugly at its specific location.

Because we were mounting rafters with joist hangers, and they're all constructed for modern milled lumber, we frequently had to trim down the tickness of a rafter to fit within the 1-1/2" stirrup of each hanger. That meant I needed to measure the tickness of each rafter within a sixteenth of an inch, and then set the depth of cut on the circular saw to exactly waste away the excess. Accurately reading a tape measure for readings under 1/2" can be tricky. It's important to make sure that the steel tab at the end of the tape is used properly, and to avoid confusing 1/4 inch from 3/8 inch.

5. Circular Saw
When making precision cuts (trying to keep margins under 1/8-inch), the most important thing is understanding kerf—the thickness of the wood removed by the blade when making a cut. When executing bird's mouth notches, I needed to constantly remind myself which side of the line was waste. Also, when making interior notches, I had to be vigilant about not running the cut deeper than the mark. It's virtually impossible to do this work without safety goggles, as you constantly need to be checking where the blade is working—placing your face directly in line with flying wood chips.

6. Hand Saw
On every bird's mouth, I had to stop the circular saw short before the cut was complete (because the cut at the top of the board is more advanced than the cut at the bottom), and finish each cut with a hand saw. Because the kerf of a hand saw is considerably less than that of a circular saw blade, it was imporant to press the hand saw blade against the line whenever I was finishing a cut.

There's a satisfying rhythm to working a hand saw cleanly. Western saws cut on the down stroke (Japanese saws cut on the pull stroke), and you need to keep the blade in line with the cut, start the stroke lightly and then accelerate into the finish. As you near the interior corner of the bird's mouth, you need to steepen the angle of attack, until the last few strokes are made straight up and down.

• • •
With Steve and Denis up on top (each working a different beam), Sarah and I worked below. Sarah would help me schlep boards from the stack in the yard, hold the tape for the critical measurements between bird's mouths, help me wrangle the boards up to Steve & Denis, keep the upstairs crew supplied with hardware, and keep my workspace clear of wood scraps (tripping over scraps with a powered up circular saw can be more excitement than anyone needs). Sarah and I could just keep ahead of Steve & Denis, and we mounted about 20 rafters before dinner.

At dinner, people remarked on how joyful the work site was and how substantial the productivity-to-swearing ratio. In all, it was a
very satisfying day.

1 comment:

papa said...

Hi Laird,
Over the years of construction projects at Monan's Rill, I've used many things to mark out lines, from an old rusty nail to a felt tipped pen. But given the choice, I always reach for one of those weird carpenter's pencils that you write about. Here are three reasons that I think these things are still around after a couple of hundred years. 1)Because the lead is narrow in one direction, it produces a fine line. 2)Because the lead is wide in the other direction, it is strong and lasts a long time between sharpenings. 3)As you use it-leaning it over a bit-the dang thing sharpens itself!

See you soon-
Dave Tracy