ROUTING TO .001"
Introduction

Router Woodworking

Introduction

Figure 3: My fence is 4 layers thick and the I-beams are as stiff as railroad track. The package is very resistant to deflection.


Figure 4: with more than 25 pounds of force near the stylus there is less than .001" of deflection.

A lot of woodwork is jig & fixture dependent. Precision routing is almost always done with some holder, jig, or fixture. Fixture component (and the fixture itself!) deflection in the .001-.003" area is a major source of error; you cannot see deflection of this magnitude so you cannot assume it does not exist (see Fig. 3). A travel indicator is called for here. Most have magnetic bases, useless for the woodworker working on substrates of wood and aluminum. I use a 15$ Chinese indicator in a holder I made. I can weigh it down if I can't get a clamp on it. If the jig component (fence, toggle, holder, crowder, etc) is suspect, test it for deflection before committing it to service.

Set the indicator up and apply a force much greater than you expect to use in the operation (see Fig. 4). See if the damn thing bends. If it does, (2-3 mils are too much) take steps to stiffen it. Clamp it (the component) in more than one place, double its section, use another material, add more hardware, change its substrate, do what ever it takes. This kind of error adds up fast. And, to be sure, we need to understand a few principles of measuring before we move on.

The indicator above, for example, is largely independent of technique; your touch has nothing to do with its accuracy. As such, if you can get it into play when investigating, it will be an advantage over other measuring devices. Most of the time we are not so lucky. Your touch, sight, and even your hearing are called upon for the close measurement. And these senses are all arbitrary and will influence the value of the measurement. This is metrology, the study and management of measurement.