TOUCH PROBE 3D SCANNING…TIPS AND TRICKS
One of the most interesting features related to the world of the CNC machines for processing marble and granite (but not only) is the 3D scanning.
Today almost all CNC softwares have a “scanning feature”; Check it on your machine.
Scanning allows to acquire the 3D shape of a solid object (marble, granite, glass, wood, etc.) and to create an STL file that can be used for the reproduction of the acquired form with a CNC machine.
3D scanning can be done basically in two ways: by using a laser scanner or a mechanical touch probe.
The laser scanning is faster than the touch probe but it’s really more expensive with the same performance. In my experience, I got to use some mechanical probes with excellent results in terms of scanning accuracy.
How does a 3d scanner touch probe work?
Before scanning an object with our CNC machine using a touch probe we have to setup some simple parameters:
– the diameter of the probe tip
– two adjacent points distance
– scanning direction (X or Y)
– scanning step between two scan lines
– zero axes coordinates ( usually set at the lowest and left-most point, if the piece to scan is seen from above)
Done this you are ready to start scanning. The machine will bring the probe into contact with the object, release the contact of the probe bringing upwards the Z axis, and the move along the scanning direction and repeat the cycle. At the end of the scan with the acquired data, an STL (Stereo Lithography interface format) file will be created.
Usually, the machine controller allows stopping the scanning at any point to restart it at a later time. Obviously, with the scanning restart, we will create a second file with the new scan data.
These files can be joined together by a software. One of the most famous is called MeshLab. Merging files with MeshLab is a very simple operation, we have to import the two STL files and use the command “Flatten Visible Layers“.
If the probe is very cheap and not professional a common problem is the clamping of a contact that prevents the resumption of the scan. In this case, it is necessary to unlock the probe manually. This occurs especially during the first scans. The probe, therefore, needs a period of “running”.
When the probe has manually unlocked the software may record also this manual touch as a scanning point. This spare point can be removed by the software MeshLab. Simply use the feature “Select faces in a Rectangular Region tool” select the point you want to delete and click “Filter -> Selection -> Delete Selected faces and vertices“. Very simple!
A few days ago we scanned a decorative stone lintel to be able to reproduce it in another block of stone, perfectly respecting the original even in its imperfections. The dimensions were X: 1600mm Y: 300mm Z: 40mm. The scan has been done with a tip diameter of 2 mm and, given the size, I did a scan with 1mm distance between two points and we acquired 235,986 points. The result was really good !!!
Below a video example, some photos of the piece and the acquired shape on screen: