CncMill

Machine Overview

3-axis OpenBuilds C-Beam CNC Router. This machine is an X/Z gantry with a moving Y-table bed. The total machine travel is X 350mm, Y 280mm, Z 160mm.

Control board is CNC xPRO Controller v3 from Spark Concepts.

There are three control buttons mounted on the front side of the cabinet; resume (green), feed-hold (yellow), estop (red).

The estop button will stop all the motion. If the machine was moving at the time the exact position will be lost, requiring a rehoming operation.

The feed-hold button will bring the machine to a controlled stop, where it will pause.

The resume button continues movement from the controlled stop of feed-hold.

Operating Instructions

The low-level stepper controller runs GRBL and is accessed by the trailing USB cable to the side. To operate it requires a computer with some form of high-level controlling software for sending Gcode.

The following is the operating sequence I [PaulEvans] found works for me.

Computer Preparations

The following steps need to be performed on your controlling computer (most likely a laptop) beforehand.

• Prepare your Gcode shape definition file using some form of CAD/CAM software. Remember that GRBL cannot perform cutter radius compensation, so this must be done by the software generating the final Gcode output. Some useful software might include:
  • https://cloudconvert.com/svg-to-dxf - convert an SVG shape into DXF
  • https://sourceforge.net/p/dxf2gcode/wiki/Installation/ - convert a DXF shape definition into Gcode (note that at time of writing the combination of cloudconvert and dxf2gcode will get confused about inches vs. mm measurement units, requiring you to "Scale All" by a factor of 25.4 in dxf2gcode before you begin - see also https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=908543)
  • http://jscut.org - convert an SVG shape definition into Gcode
• Obtain a copy of Universal Gcode Sender. There are two forms available, "Classic" and "Platform". I prefer the more featured "Platform" version.

The GRBL controller now has control of spindle speed, so don't forget to include an appropriate M03 instruction in the output to set it.

Preparing The Machine

Once at the machine, the following setup needs to be performed to get the machine ready for operation.

1. Connect the trailing USB cable to the computer you'll be running UGS from. Check that it appears as a new serial port - e.g. a new /dev/ttyUSBn device will appear on Linux.
2. Start UGS. It should detect the serial port. Configure it to "GRBL" firmware type and "115200" baud communication. Press the Connect button. UGS should now be reporting that the machine is in "Alarm" state - don't worry, that's just how GRBL powers up for some odd reason.
3. Send the $X command to reset that alarm. This will be found in the "Machine" menu under the "Actions" sub-menu item.
4. Send the $H command to start the homing cycle. This will align all the axes so that the controller knows where they are.

At this point the machine is now ready to perform a milling job.

Running A Milling Job

Now the machine is ready to go and you have your Gcode file, you are ready to actually cut it.

1. Load the Gcode file into UGS (the "Browse" button in the toolbar of UGS Platform).
2. Mount the workpiece on the Y-bed under the machine.
3. Using the jog controls in UGS, move the cutting head to the appropriate "zero" reference point on your workpiece.
4. Once all three axes are aligned relative to the workpiece, press the "Reset Zero" button. Note be sure not to confuse it with the similarly-labelled "Return to Zero" button; which performs an entirely opposite operation!
5. Start the spindle controller by pressing its green "Run" button. Note that GRBL now has control of the spindle speed, so it will start at speed 0 to begin with until the G-code program instructs the spindle to begin.
6. Double-check the positioning is correct, and if you're happy, hit the green "Go" button in UGS to start the job.

You may find it helpful to perform a "dry run" first to check that everything will be OK. Without the spindle running or the workpiece secured to the bed, the "Go" button will still make the machine move around. You can watch whether it appears to be going in the right places - the "Visualiser" window in UGS may help you to confirm this too. For extra safety against the chance of crashing the head into the bed, run this first without the endmill tool in the spindle, or at an increased Z height away from the bed. If you do run this dry-run at an increased Z height, don't forget to reset it back to the working height to do the real run.

Inventory

A (probably incomplete) list of the milling cutters:

• Drills 0.4mm - 1.2mm in 0.1mm steps
• Cutters 1.5mm - 3.175mm
• Endmill 2x6 (5 pcs)
• Endmill 3flute 3x6 (no box)
• Endmill 3flute 5x6 (no box)
• Endmill 3flute 6x6 (no box)
• Endmill 3flute 7x8
• Endmill 3flute 8x8
• Endmill 3flute 9x10
• Endmill 3flute 10x10
• Endmill 3flute 12x12
• Rounded endmill R1x6
• Rounded endmill R3x6
• Rounded endmill R5x10 (2 pcs)
• Ball nose endmill R10x35 ((I don't know why we have this; it's too large to fit in the spindle))
• T-slot cutter 16x6

Internal Notes

Front panel cable:

Colour	Function
Black	GND
Red	5V (unused but may be useful for expansion)
Yellow	Feed hold
Green	Start/resume
White	Estop
Blue	Spindle PWM

How it's all wired together (motors, control board, spindle drive) [| CNCRouterWiring.pdf]

The spindle motor is believed to be mains voltage, three phase, probably star-wired. It is driven by a Huanyang VFD. Manual here

See Also

• GRBL - [1]
• Universal Gcode Sender - [2]