CNC Router or Waterjet for Sink and Cooktop Cutouts

Nothing about a sharp inside corner is forgiving in stone, and no machine changes that. A fabricator weighing a CNC router against a waterjet (the comparison laid out at austin countertop fabrication pdc 2015) is really weighing how each one handles the corners of a sink cutout in a countertop in Austin, TX.

Why sharp corners crack

Granite, quartz and quartzite are brittle. A square inside corner concentrates stress, and a heavy sink, a thermal swing from a hot pan or slight cabinet movement can start a crack right there. The fix is a radius. A rounded corner spreads the load, and most shops cut every cutout with a corner radius no matter how square the sink looks from above.

The CNC router

A CNC router holds the slab on a vacuum table and uses a diamond bit that travels along the digital template. It handles sink cutouts, faucet holes and the cutout edge quickly, often in a single setup. Water cools the bit and carries the dust away. The limit is the bit itself. A bit has a diameter, so the smallest inside radius it can cut is about half of that, and very tight shapes need a smaller bit or a different machine.

The waterjet

A waterjet cuts with a thin stream of high pressure water carrying abrasive garnet. It puts no rotating tool against the stone, so it can cut very tight radii, narrow slots and decorative shapes. A farmhouse apron sink or a tight cooktop opening in solid surface or porcelain is a good candidate. The cut is slightly tapered, and the edge usually needs a pass of polishing afterwards.

Undermount reveals

An undermount sink sits under the stone, and the reveal is the small strip of sink rim showing past the cutout edge. Setting the cutout slightly larger than the bowl gives a positive reveal, and setting it flush gives zero. Either choice has to be set in the file, because it cannot be adjusted once the stone is cut. A positive reveal also leaves a ledge where crumbs collect, which matters in a kitchen that is used daily.

Which machine gets the job

Most sink cutouts go to the router, and the waterjet takes the difficult shapes and any material the router bit struggles with. The question for a shop is less about preference and more about the sink in the box, the corner radius required and what the stone will tolerate. On delivery day it is fair to ask which machine cut the opening, then look at the corners, which should be rounded and smooth, with no chips along the edge of the cutout.