# SurfaceFabrication.com |

## Magazine Article

Cutting Circles, Arcs And Other Geometric Shapes
The Stone Shop

Figure 1

Figure 2

Many kitchens today contain arcs, circles, large radii, etc. The problem many fabricators run into when cutting is the layout of these unusual geometric shapes. The following is a basic procedure that I use for making these cuts.

TEMPLATING AN ARC

There are many ways to lay out an arc. If you are mathematically inclined, you can use basic geometry calculations. For those of you who can’t remember that far back, here is a basic calculation. (OK, get ready — your brain is going to hurt!)

In terms of mathematics, to lay out an arc we use a coordinate system placing the chord (line segment between two points on a given curve) along the x-axis with the value of r representing the length of the radius. The perpendicular (90-degree angle to a given line or plane) distance from the center of the chord to the arc is the represented value of h. Therefore, the center of the circle lies at the coordinates of (0, h-r). Here is the equation:

x2 + [y-(h-r)]2 = r2

Next, we solve for our y coordinate in terms of x as follows:

y = √(r2 – x2) – r + h

Stop rolling your eyes; there is an easier method to laying out an arc and it doesn’t require a Ph.D. in math. You can simply template the arc. If you take a strip of luaun and and turn it on end, you can bend it to the desired arc or radius. Next, attach several support strips to hold it in place. (See Figures 1 and 2.)

CUTTING AN ARC

Once the template has been made, it’s time to cut the arc. The following is a basic procedure.
• Lay out the arc or circle on the stone by tracing the template with a white-out marker.
• Set up a small hand saw with a 5-in. contour blade. Make sure the blade is set up so that the contour (convex side) is facing in toward the motor of the saw. For proper mounting see the instructions equipped with the saw.
• Connect water to the saw and plug the cord into a GFCI equipped outlet. Check the GFCI button on the cord of the saw to make sure it is working correctly by pressing the test button. Caution: You can only test the GFCI when it is plugged into a live outlet. It will not test properly unless plugged in.
• Adjust the depth of the blade so that it cuts all the way through the thickness of the stone.
• To start cutting, position the saw about ⅛ in. to the outside of the cutline. Hold the saw so that the blade is not touching the top. Turn the water on and start the saw by depressing the start button. Slow-plunge the blade into the stone, being careful that it does not kick back.
• Once the saw blade is all the way through the stone, slowly push forward following the marked line staying ⅛ in. to the outside. When cutting a tight radius, make sure that the back of the blade does not hit the line as you make the turn. In other words, watch both the front and back of the blade as you are cutting.
• As you reach the end of your cut, make sure the piece is supported on both sides so that it does not snap off as you reach the end of the cut.
• To clean the cut, treat it like you would an undermount sink cutout. Clean up with a zero tolerance bit, and finish as you would a normal edge.
While the math behind the fabrication of difficult shapes is interesting, you don’t have to be a rocket scientist to cut an arc. If you run into problems with arcs, just remember to go back to the basics and template your cuts.

About the author: Frederick M. Hueston is a worldwide expert on stone installation, failures, fabrication and restoration. He is the founder of the National Training Center for Stone & Masonry Trades (ntc-stone.com) and Stone University (stoneuniversity.com). He can be reached at Fhueston@aol.com.