CNC Stone Machines – Eliminate Visible Lines on Granite Profiles

September 16, 2021 0 Comments

It is a common problem for stone kitchen and bathroom countertop manufacturers that their CNC machine leaves visible lines after profiling the marble or granite edge, resulting in a not as glossy finish as desired.

Lines are unavoidable on profiles with a large flat section like the ‘T’ profile but also on all other profiles more or less. The visibility of the lines depends on different factors. One is the stone itself, regardless of whether it is natural stone such as granite and marble or artificial (designed) stone. CNC diamond tools are another important factor in the finishing result. With brand new diamond tools, the lines are minimal, but will eventually develop lines that are noticeable and unacceptable to most stone manufacturers and their customers.

On some profiles and stones, it is possible to limit the lines to a minimum by running the polishing wheels back and forth 3-4 times and changing the Z-value up and down by a minimum amount (0.005mm) for each pass, which might not be possible to do with all profiles.

Another option is to manually run a 400 grit pad after the CNC has run all the metal wheels and before the buff wheels. That helps keep the polishing tools in good shape, but it’s extra manual work that disrupts the normal workflow on the CNC machine.

Veneering your profile diamond wheels on a regular basis with the proper facing stones will help keep lines to a minimum.

There are also special tools called line breakers and line breakers, to name a few that can result in a better finish.

If you compare the process of polishing by hand to the way the CNC machine works on a profile, then you can recognize where these lines are coming from and why it is difficult to get rid of them. In the CNC machine, the tool rotates in the same direction as the movement of the machine. There is no cross movement of the tools and the movement of the CNC machine.

Just see what happens when you polish by hand, the tool rotates through the movement you make by hand. That movement is what removes the lines and that is not possible with a CNC machine until someone designs a machine head that works the same way as manual polishing. It is doubtful that this is possible.

You can’t really compare a “T” or “V” shaped profile produced on a CNC with a profile polished by hand or with a line polishing machine. The CNC profile is never that shiny and will need to be touched up by hand if you want a high quality finish.

If your CNC machine is equipped with a saw gearbox, you can get an adapter made to connect the standard magnetic drain board polishing tools to run on the T-profile. As long as your CAD-CAM-CNC software lets you allow to program correctly, especially the entry and exit of the tools are critical, so as not to crash the machine. The result is near perfect, but the arris or pencil round still needs to be finished by hand afterwards.

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