Surface Measurement With a Probing Grid
Material is rarely flat. Rolled brass, cast parts, a sheet clamped at the corners, a spoilboard that has seen some use. Over a 300 mm panel a few tenths of variation is normal, and a few tenths is the entire depth of an engraving.
Surface measurement solves this by probing a grid of points across the workpiece and correcting Z from the result. It requires a probe on your machine.
Switching the function on
The measurement grid is hidden by default.
Click the gear icon at the very top of the CamDRAW docker, next to the logo. On the General tab, tick Measuring grid, then click Save at the bottom left of the window.
The measuring grid section now appears in the docker.
Creating a grid
Select the drawing objects you want covered, enter the measurement values, and create the grid. It is placed automatically over the selected objects, with the measuring points shown as dots and the edge of the grid as a rectangle.
Selecting nothing creates a grid over the entire CorelDRAW page, which is what you want when scanning a whole workpiece surface rather than one engraved area.
The settings
Round workpiece switches the grid to a circular shape.
Number of points X and Number of points Y set the grid density. More points means a better height map and a longer probing cycle.
Border distance X and Border distance Y set the margin between the selected objects and the edge of the grid.
Z safety height (WCS) is the height the probe moves to between measuring points.
MinZ is the lowest point the probe is allowed to reach, a safety limit in case a point finds nothing.
Z increment (X) and Z increment (Y) are additional parameters for an extended measuring cycle.
Probing feed rate is how fast the probe approaches the surface.
An information area below shows the resulting X and Y spacing between points and the total number of measuring points, which is the quickest way to judge whether a grid is too coarse or unnecessarily slow.
The buttons
Five icons sit below the fields: create the measuring range, update it after changing values, delete it, show or hide it on the page, and Z-Auto to select the first measuring point.
The red point
One measuring point is drawn in red. It is an adjustable reference point, used for example to set the Z zero on the machine before the measurement runs.
Its X and Y coordinates are available as postprocessor parameters, so the position can be written into the program.
How the data reaches the machine
CamDRAW defines the measurement parameters. The actual probing is done by your control.
All measurement values are available as placeholders in the G-code, including the number of points in each direction, the grid spacing, the corner position, MinZ, the safety height, the Z increments and the probing feed rate.
The usual approach is to write those parameters into the program and then call a subroutine on your control, which performs the measurement using them. Exactly how the subroutine works depends on your controller.
The machine setup file
Every time a program is generated, CamDRAW writes a second file alongside it, intended for setting up the machine. Its contents are defined in the postprocessor under the machine setup section, and all placeholders are available there too.
This is where a probing cycle usually belongs. Run the machine setup file before running the job file, so the surface is measured before the engraving starts.
When a depth regulator is the better answer
Probing is not the only way. A mechanical depth regulator rides the surface and keeps the tool a fixed distance below it, which needs no probe and no measurement cycle.
It is faster and simpler, but the floating nose touches the workpiece. On soft or finished surfaces where a mark would be unacceptable, probing is the option that leaves the material alone.
If you are unsure how to connect this to your controller, our support team helps with adapting the postprocessor and the setup file to a specific machine.