Overview
Finding the center of an existing hole by hand can take time, especially when accuracy matters. With SourceRabbit Focus and a 3D Touch Probe, the CNC controller can measure the hole from multiple directions and calculate the center point digitally.
This is useful when you need to continue machining from an existing feature, align a job to a real part, or recover the work offset from a previously drilled hole.
How It Works
Focus moves the probe inside the hole and touches the inner wall from opposite directions. By comparing the measured positions, it calculates the X and Y center of the hole and lets you use that position as your working reference.
The video below shows the process with a 3D Touch Probe on a GRBL CNC setup.
Before You Start
Make sure the 3D Touch Probe is connected correctly, the probe input is configured in GRBL, and the probe can trigger reliably before running the routine. The probe tip must be able to touch the inner wall of the hole without colliding with clamps, fixtures, or the workpiece surface.
Start with conservative probing speeds and verify the direction of movement before relying on the measured center for machining.
Wiring the 3D Touch Probe
With the Rabbit Board 4-Axis, connect the 3D Touch Probe to the probe pins. The probe input is opto-isolated, like the terminal switch inputs, which helps protect the signal from external electrical noise.
You can use Normally Closed or Normally Open probes. Normally Closed wiring is recommended because it offers safer behavior if a wire breaks or the probe circuit is interrupted.
Final Check
After the center is located, confirm the new position with a safe Z height before starting the next machining operation. If the result does not match the expected hole center, stop and check the probe wiring, probe diameter, GRBL probe input, and the selected probing routine.