CNC Machines for Stone – Eliminate Visible Lines in Granite Profiles

It is a common problem for stone kitchen and bathroom countertop fabricators that their CNC machine leaves visible lines after profiling the marble or granite edge which results in a not so shiny finish as desired.

The lines are unavoidable on profiles with a large flat section like the ‘T’ profile but also on all the other profiles more or less. How visible the lines are depends on different factors. One is the stone itself regardless if it is natural stone like Granite and Marble or manmade (engineered) stone. The CNC diamond tools are another big factor of the finishing result. With brand new diamond tooling the lines are minimal but eventually they will develop lines that are noticeable and unacceptable for most stone fabricators and their clients.

On some profiles and stones it is possible to limit the lines to a minimum by running the polishing wheels forwards and backwards 3-4 times and changing the Z value up and down by a minimal amount (0.005mm) for every run, which might not be possible to do with every profile.

Another option is to manually run a 400 grit pad after the CNC has run all the metal wheels and before the polishing wheels. That helps to keep the polishing tools in good shape but it is extra handwork which disturbs the normal workflow on the CNC machine.

Dressing the profile diamond wheels on a regular basis with the right dressing stones will help to keep the lines to a minimum.

There are also special tools called line-breaker and line-buster to name a few which may result in a better finish.

If you compare the hand polish process with the way the CNC machine works on a profile then you may recognize where this lines are coming from and why it is hard to get rid of them. On the CNC Machine the tool is spinning in the same direction as the machine movement. There is no cross movement of the tools and the CNC machine movement.

Just see what happens when you hand polish, the tool spins across the movement you do by hand. That movement is what gets rid of the lines and that is not possible with a CNC machine until someone designs a machine head which works the same way as hand polishing. It is doubtful that this is even possible.

You cannot really compare a “T” or “V” shape profile produced on a CNC to a profile polished by hand or a line polisher machine. The profile from the CNC is never as shiny and will need to be touched up by hand if you want a high quality finish.

TIP: If your CNC machine is equipped with a saw gearbox than you can get an adapter made to attach the standard magnetic draining-board polishing tools to run them on the T-Profile. Provided your CAD-CAM-CNC software allows you to program that correctly especially the entry and exit of the tools are critical, not to crash the machine. The result is almost perfect but the arris or pencil round still needs to be finished off by hand after.