Popular Woodworking 2004-11 № 144, страница 34

From the Bench

Testing Your Layout Tools

Is your square really square? Is your straightedge straight? Tools that have been trued make woodworking easier.

A couple of years ago, while demonstrating edge jointing using hand planes, the shot edge appeared to be slightly convex when I checked it with my wooden straightedge. I don't usually have this problem, so after a couple of tries, it suddenly occurred to me that I hadn't recently "proved" my straightedge. Somewhat to my embarrassment, a quick check revealed that the problem was with my straightedge, rather than the shot edge.

I wish I'd been clever enough at the time to pass this off as a planned "object lesson" for the observers, but I'm just not that fast on my feet. However in the end, I think it did demonstrate the desirability of proving our layout and testing tools - especially when doing critical work.

The need for accuracy in woodwork is often discussed, but far less often do we demonstrate how to make and prove our layout and testing tools for when we need to get accurate readings on our work.

Why Make Layout Tools?

The question arises, of course, that given the fact that wooden straightedges can go out of true over time, why would one bother with them? For one thing, it's possible for you to avoid purchasing factory-proven straightedges, particularly long ones, which can be quite expensive. That expense can be hard to justify, especially if you don't frequently need a straightedge on that scale.

Secondly, if kept to an appropriate scale, wooden straightedges can be a lot lighter for

Accurate layout tools lead to accurate woodworking.

Learning to test - or"prove" - your tools is a fundamental skill.

ease of handling and won't mar your work if you accidentally bump the workpiece. Additionally, if made with a little thickness, the straightedge will stand, on its own, on the surface being tested, so that you can move freely around to get a good visual read of the fit between the straightedge and the work. Carefully selecting straight-grained, relatively stable, quarter-sawn stock can go a long way toward minimizing the tendency of a wooden straightedge to go out of true. Honduras mahogany is a good choice.

You will still need a shorter metal straightedge for knifed layout lines for critical cross-grain work, but your wooden straightedges will be suitable for any pencil layout lines and for testing surfaces.

by Don McConnell

Don builds furniture and does ornamental carving in Mt. Vernon, Ohio. Formerly at the cabinetmaker's shop at The Ohio Village, he remains an avid student of the history of the trade, tools and shop practices.

Photo by Al Parrish

It could be argued that you could avoid the need for proving your layout and testing tools by purchasing tools that have been factory proven (or calibrated) to certain tolerances. And that often can be a good investment. But even if their expense can be justified, we can't be absolutely certain they are accurate after being kicked around on the workbench for a while, or being dropped on the floor. A solidly built square may retain its accuracy after a fall to the floor, but wouldn't it be better to know for certain, rather than just hoping it to be so?

Prove Your Tools

How did I prove my straightedge ? Well, I simply laid it on a smooth, light-colored surface and traced along its reference edge with a sharp pencil. I then rotated the straightedge around its longitudinal axis and checked that same edge against the pencil line. The beauty here was that any error, or deviation from straight, was doubled in magnitude, and the continued on page 34

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Popular Woodworking November 2004