The Hand-Crafted Curve

   While the technology is amazing and certainly produces superb results, it will never completely replace hand fabrication. However, the CNC also set a benchmark for precision cutting, which today's non-CNC shop may have difficulty competing against.
One area that often gets attention in CNC promotion is in cutting a large radius for, say an island or a bar-top seating area. However, using basic hand tools, it’s possible to produce mathematically perfect radius cuts.
 

Making a template for a radius cut is an exercise in simple, 1:1 scale geometry. After measuring for precise board-and-router placement, the router – attached to the long board – traveled in a perfect arc to make the template. (Photos courtesy Reuben Flax)

  How? First, it’s a process of creating a template out of plywood and then using it to shape the stone. The final touch will be profiling the edges and polishing them to a mirror shine. The total time for this project is going to depend on your familiarity with these tools and your speed as a polisher.
   The first step is cutting the template. To start, fit a wood router with a standard 1/2" fluted wood bit. Then, attach the base of the router to a radius jig that's available from most Big Box stores. (The one that’s pictured is homemade.)
   The jig doesn't need to be anything fancy. The idea here is to have some way of attaching the router to a very long stick – creating, in effect, a giant compass to describe a large circle. Here’s how I did it with a recent job.
 

You can buy a radius jig at a large hardware outlet, or – like this one – it can be made in the shop.

  
The stone to be cut was 84” wide with a 6”-deep radius bump-out, with a flat shoulder on each side of the bump-out. After placing a sheet of plywood on my saw table, I marked two points 84” apart and then marked a point on the centerline 6" close to the edge.
   I took a long board and screwed one end of the board to the far end of the saw bed. Then, using a little trial and error, I swung the board back and forth until the end was touching – exactly – the two end points and the center point. In this case it was 128”.
   Next, I screwed my router to the long board, and – measuring from the outside edge of the router bit – I marked a point 128” away from the router on the board. I set a screw through the point; I then made a dry run with the router bit set just above the surface of the plywood so I could visually inspect that the bit was following the correct path. Once good, I plunged the bit and made my cut, being careful to keep even pressure on the router.

After finishing the flat parts with a jigsaw and a light sanding, the template is ready to go.

   I was careful to stop the router as I got close to each shoulder; I finished up the flat parts of the shoulder with a jigsaw. A light hand-sanding of the edge to knock down any splinters, and I’d just created a perfect template.
   For the second step of the process, I placed the template on top of the stone and traced the layout with a white-out pen. I removed the template and cut the stone within 1/4” of the line, in two step-cut passes, using a power hand saw with a 5" blade. (For very tight radii a contour blade would be used, but in this case a straight blade worked fine.)

With the template clamped in place, it’s time for the stone router to follow the edge for the rough cut.

   With the stone cut to rough shape, I carefully cleaned the surface and set my plywood template back in place. I checked to make sure it lined up exactly, and if there were any problem areas that showed up; this is the time to compensate by shifting the template around. After doing so, I clamped the template to the stone tightly so it didn't move around. This is important, so don't be cheap on the clamps.
   
I then put a zero-tolerance wheel on my stone router and ran the edges along the template. For this step I used a new router bit called the Rubenator (which is a shameless plug for my product but it works). In about three minutes, the entire radius was cut exactly to shape and ready for a profile and polish.
 

You should include a final pass with a zero-tolerance wheel. I’ve devised my own model, called the Reubenator.

  This job called for a quarter-round profile, so we removed the plywood template and switched to the quarter-round router bit to finish the shape. After shaping, all that was left is some hand-polishing using a rigid backer and light pressure to ensure that the shape stays true.
   It’s very easy to create a flat spot in the radius when polishing with lower grits like 50, so it's always best to go slow and check your work often. If you create a flat spot in the stone, don't worry; you can work it out to one edge or the other. However, I’d recommend practicing this first on some scrap before trying it on a paying job.
   CNCs are nice … but for those of us who don't have them, there's no reason to compromise on your quality. These techniques can be used to create just about any complex shape be it ellipse or full circles.
 

After the final pass with the stone router, the piece is ready for profiling and polishing – and, from there, to the final install.

  I’ll be back in a future issue to demonstrate how to do a 10-minute sink cutout, ready to polish by hand, with accurate repeatable results using basic hand tools.

 Reuben Flax is a partner in Sinai Marble & Granite in Baltimore, Md. He is the co-inventor of innovative tools for the stone-working professional which can be purchased through his Website. You can also watch videos of all of the techniques covered in this article. Special thanks to the Stone Fabricators Alliance for their help and knowledge that directly contributed to the creation of this article. To ask Reuben a question or comment on this article, go to www.stoneadvice.com.

This article first appeared in the April 2008 print edition of Stone Business. ©2008 Western Business Media Inc.