7 STEPS TO UNDERSTANDING ROUTING
Most of the important principles of routing are not about routing or routers! Rather, they are about understanding and managing the materials to be routed. Routers, due to their precision and bizarre secondary and tertiary reference systems, have put a new critical emphasis on skills other than routing! Namely, material prep, work confinement, metrology, layout, setup, safety, drilling, jog design and fixture making. I think you see where I am going. The aforementioned can take days or weeks, the routing itself seconds to minutes, max. So where would spend the time with your students?
A router can’t find its pathway with both hands. They need help. The cutter, via an accessory, (edge guides, templates, and so forth), must reference off of some mechanical edge or surface. Fortunately, there are many accessories that will expedite the process. All of them require a calibration cut, however. The cutter extension, and edge guide’s reach, a collar guide bushing’s position, are all approximations. Metal working machines can find target without calibration; woodworking tools cannot. In either case, the machines reference (directly or indirectly) from the edges of surfaces of the work. As such, the dimensional and angularity of the work is critical.
If like elements of a project have been poorly prepared all like cuts applied to them will vary. Quality material prep is therefore important. And it all starts at the jointer and planer; you need both. Ignore one or the other and you might as well have neither. Expensive time and space consumptive? Yes, but routers and every other tool in your armamentarium require the work to be precisely prepared.
There are 2 essential routing travel options. The work can travel by the cutter, fixtured or unfixtured. Or the router can do its cutting directly on the work. There are hybrid configurations too, but the principles of work piece isolation and confinement are typically the same in all instances. A workpiece has 12 degrees of translational freedom. And any appliance holding that workpiece also has 12 degrees of freedom. Key here is to address as many modes of confinement as is practical. The 12 degrees of freedom include slip (left/right, in/out and up/down) and spin. The work can spin (CC and CCW) on or off any of its 3 central axes. The unit forces on your work, being routed, can vary unexpectedly and substantially. Your unleashed pet can run amok. Your work, unleashed, can bash you in the nose.
Whether knifed, inked or penciled, scribes are all approximations. Their widths and locations are your best guesses, again! I use them to verify I’m in the vicinity, not to locate my router bit. There is no way to precisely locate and scribe a line to better than ~.010″. A router bit has a vague cutting circle. You can only approximate its location with respect to the center of your scribe lines. Routing inaccuracies are necessarily the result of trying to line up the cutter with a best guessed line. So now what? Create the routing setup on spare parts, take a cut, then measure. Measurements can be proven to be within .002″ on wood and to better than tenth or metal and plastic. That, you can count on. Adjust the set up as needed, duplicate the setup on the work and all likes cuts will be like. Use your scribe lines to affirm consistency not as finders.
The art of measurement and method. Some of these tools can be used for layout and setup. I use them to measure. Precision ground squares, straight edges, calipers, parallels, compasses, and scales are not designed as scribe guides. Their edges are to be preserved. Lesser grade tools cane be used for layout. Though sweet measuring tools are enjoyable, appreciate, that money does not buy accuracy, techniques does.
Use metrology tools to prove your cuts and setups. Most router bits are capable of cutting to within .002″ of their net diameters. Edge guides, collars, bearings and sub bases can position your machine that close too. So why not exploit that accuracy where it’s warranted.
This setup is for morticing; it’s strikingly analogous to the cross cut jig above. The work immobilization measures are about the same. (We’re looking at the obverse). The work cannot rotate on any of its axes. Its north end is its only open gateway. Its (marked yellow satin sample) essentially paralyzed. The fixture is flipped upside down and clamped down on the oak pad and plastic platform. The back side of fence rests against the edge of the bench and keeps it from turning. Now the plunge router, (on the top side of the platform), its 2 edge guides and platform-stop-slides, confine the router’s excavation to 1 mortice. Ducky, no?
The skill to cut the mortice has bend reduced to cretin level. Along with that: Built-in safety. Get the work isolated, firm up the fixture’s residence, design in the travel limits of the router and safety is automatic. A setup? In spades.
Jigs and Fixtures
Since the router is nearly blind, we need some seeing eye jigs to help it find its way. Displayed here, are jigs for routing, sanding and drilling. Sanders and drills have similar confinement and work location problems. One central problem: Woodworkers are not trained to make jigs; they’re trained to sand, saw, shape, drill, joint, join and plane. So where do your learn this stuff? You trial and iterate, go to school, read books, the WWW, or maybe take a lesson from me.
It is remarkable, that while substrates and components look like they came from the machine shop; I made them with woodworking tools. The raw material (aluminum, wood, and fabric phenolic), was bandsawn, routed to squareness and drilled where necessary.
Now and yet another degree of separation, you must be a good driller to be an ace in RouterDom. Routing depends on quality fixturing. Quality fixturing is adjustable and screwed together, less often its components are faceted (resting in milled nests). As such, components are screwed to their substrates. If you can’t locate holes on common centers, your components will be arranged helter skelter. Drilling is therefore part of routing.
Adherence to the above principles will get you the keys to Routing. Moreover, you’ll be prepared for almost any ordinary work in the woodshop. Sure, you must use the right router, guide system and cutter. But if you’ll accept the fundamentals above, you’ll spend little time routing. And if in doubt, waste just and 1/8th”/pass (or less) until you understand the dynamics. With very light cuts, in many situations, there is so little power transmitted back into the router, (Newton’s 3rd law), that you can rout in any direction without adversity. It is the smartest way to begin the art.