Chris Cockrum's CNC Control
When I look for content to add to this website, I look for content that will ultimately benefit the users of this site with additional information. With the various control methods that Chris brings to the table, I am overjoyed to add his methods to this website. Chris implements a simple and effective Z-axis homing plate, router control and some fine examples.
For more on Chris' genius, check out his website.
How can the z-axis be homed or zeroed in the most obvious place, the work surface? Before I get to the obvious answer, let me digress. I get this question in my inbox frequently. Well, as we all know, homing is a process where something on a particular axis moves towards a switch and then moves close enough to press the switch. This provides a signal to the computer where the software will stop the axis from moving and then zero that axis. With gantry machines (let's say the gantry motion represents the x-axis), the gantry would hit the switch that is mounted on the table at one end. This provides a very accurate position for the x-axis, and since the y-axis also moves along a horizontal plane with respect to the material being cut, this also provides an accurate position. But, the z-axis moves away and towards the workpiece, usually in a vertical motion, and to make matters more complex, the workpiece can be any thickness. At least the x and y can have an origin, but this is not true with the z-axis, unless you use the top of the z-axis as the origin. But isn't is better to make the workpiece top surface the origin? My technique is to manually zero the bottom of the end mill on the surface of the workpiece. Of course, this is a terrible way to zero the z-axis because the precision is completely random. Chris implemented a z-axis plate with a clip wired to the plate to close the circuit when the end mill touches the plate. The thickness of the plate is easily determined and this measurement can be consistently used in the CAM toolpath specifications for the z-depth.
You will also notice that Chris controls his router. I have been meaning to add this functionality to my CNC machine, but it usually just finds its way to the bottom of m y priorities. Thanks to Chris, he provides a schematic for this and the z-axis homing plate. Check it out at his website including whatever he is working on at the moment... banjos, large gears for wall mount wooden clocks, etc. I can't wait to see what he is working on next.