Cutting Large Ellipses with a Router
Need to cut an elipse for your next project? We have some suggestions on how to get the perfect size and shape you need.
Getting tired of building boxes? Aren't there a few other shapes that a woodworker can make? Of course, there's a reason why 90 and 45 degree angles are so popular with woodworkers: We know how to make them, and our favorite tools do, too. An elliptical frame or coffee might make a refreshing and challenging departure from same old rectangles and squares. But the question is, how do you turn a piece of wood into a nice, smooth, mathematically correct shape that isn't made up of straight lines?
Maybe you've tried the old "two thumbtacks and a piece of string" method. You know the one: Tie a piece of string into a loop and use it along with two tacks positioned at the foci of the ellipse as a guide for tracing the shape. Most would agree, though, that this works better in theory than in practice. If you’re not handy with algebra, getting the tacks in the right place and the string tied into the right sized loop is nothing more than time-consuming guesswork. And when you do get the shape drawn out, what do you have? A drawn-out shape. You still have to cut it, and that usually means freehand, with a jigsaw or band saw – and then sand, rasp, plane or whatever until (hopefully) it turns into a smooth, fair-curved ellipse.
Fortunately, there's a much better way: With an "ellipse jig" and a router you can define and cut an elliptical shape in one fell swoop. An ellipse jig (sometimes called a double trammel jig) isn’t new technology by any means. It's essentially a big compass that uses two sliding pivot points to guide a router along the perimeter of the ellipse. You’ll find plans for constructing, and tips on using this time-honored router accessory in most router technique books.
Making your own ellipse jig is a viable option, but it's a little more work than most folks want to spend setting up for a project. There's a fair amount to an ellipse jig. You need a trammel arm that can be attached to your router, a jig base with two very accurately cut channels to guide the two moving pivots, the two moving pivots themselves, and some way of attaching them to the trammel arm. In other words, making an ellipse jig that works well the first time, and will last through several projects, can eat up a fair chunk of shop time.
And why bother, when you can just send out for the Rockler Ellipse Jig? It's an affordable piece of equipment, and it's all set to go. You don't need to know (or do) any math, you don't have to pre-draw the ellipse, you don't really even have to understand how the jig works – the instructions are printed right on the jig, and walk you through the entire process one step at a time. All you really need to know is how to use a router, and how big of an ellipse you want to make. And you'll have a lot of range there if you also pick up the Large Ellipse Base. This add-on base greatly expands the range of larger ellipse proportions the jig can handle, increasing the maximum difference between the length and width of the ellipse from 8" to 14".
All of the jig's moving parts are precision machined from tough phenolic resin – an aspect that would be hard to replicate in a shop. The phenolic material slides easily, so you can concentrate on keeping the router moving at the appropriate speed. And it won’t wear out, even if you take after ellipse-making with a vengeance. And once you see a couple of near-mathematically perfect ellipses appear quickly, easily and almost magically before your eyes, you may decide to do just that.