Tool Review: Acu-Arc Adjustable Curve

Drawing curves and arcs for furniture has always been a challenge. I have a set of French curves that are good for details, but curves that are larger than 10″ are a challenge. I have long wanted a set of Copenhagen Ship Curves, but I’m going to have to make those myself or save my pennies for a while.

Until that day comes around, I’m going to stick with using my Acu-Arc Adjustable Curves. This clever product is made from 12 layers of butyrate that are all sleeved together. When you bend the tool into a curve (it has been reliable down to a 6″ radius) the tool holds that shape , thanks to friction. Then you can strike your cutline along the tool’s edge. If you lift the tool up without too much violence, it will maintain its curve to mark the same shape on other workpieces.

The Acu-Arc excels at marking curves that accelerate , not just simple radii that can be made with a compass. And it’s fantastic at smoothing out a curve that you have plotted at several points. It will connect your dots smoothly, which can save time compared to hand-sketching your details.

To use the tool, I’ll typically start the bending the tool at its fixed end , where all the layers are bound together in blue plastic. Shape the curve from there out to the end that is unconstrained. Then, when you are ready to mark your line, do it in small sections , don’t mark the entire curve at once or you’ll surely lose your setting. Press the tool firmly to the work and slide your pencil (or technical pen) along the edge near your fingers. Lift your fingers, move them down the curve and repeat the process.

When you are done with the tool for the day, straighten it out using your fingers.

Acu-Arc makes two versions that are suited for furniture: an 18″-long version and a 36″-long version. These two are available from Lee Valley Tools. There are longer versions used for building boats that go up to 72″.

What I like best about these little tools is that they free me from thinking about my furniture with a ruler. It’s easy to build austere straight-line stuff if all your tools have straight edges. The Acu-Arc lets you create almost any curve. Then you can lay it on your work to ponder: “Do I like that curve?” That’s a difficult task to do with the way so many woodworking magazines show how to draw a curve , a bendable stick, two nails and three hands. No wonder we stick with straight lines.

– Christopher Schwarz