Shield CNC V3 for Arduino UNO, 4 axes, compatible with A4988 and DRV8825

The CNC Shield V3 turns an Arduino UNO board into a complete controller for CNC milling machines, laser engravers, plotters, and other stepper-motor projects. It mounts directly on top of the Arduino UNO board or any compatible clone based on the ATmega328P. It is designed for the open-source GRBL firmware, which interprets G-code commands received from the PC and generates the step and direction signals for the drivers.

The board features 4 slots for A4988 or DRV8825 stepper motor drivers, for the X, Y, Z, and A axes. The A axis is configured via jumpers, either to duplicate one of the X, Y, or Z axes, useful for machines with two motors on the same axis, or for independent control on pins D12 and D13, with dedicated firmware. Each slot has jumpers for microstepping selection, up to 1/16 with the A4988 and up to 1/32 with the DRV8825, and a 4-pin motor connector.

The shield also provides connectors for 6 limit switches, two for each X, Y, and Z axis. It has outputs for spindle control (enable and direction), an output for coolant, and inputs for the Abort, Hold, and Resume buttons. It also includes a header for emergency stop (E-Stop), plus access to the I2C and serial pins. The motors are powered separately, through a screw terminal, at 12 - 36V DC, while the logic section receives 5V directly from the Arduino board. It is an affordable and easy-to-wire solution for building a DIY CNC, laser engraver, or plotter, suitable for hobby use, educational projects, and prototyping.

Specifications:

Model: CNC Shield V3

Compatible board: Arduino UNO R3 and ATmega328P clones

Motor supply voltage: 12 - 36V DC (maximum 35V with A4988 drivers)

Logic power: 5V from the Arduino board

Driver slots: 4 (X, Y, Z, A)

Compatible drivers: A4988, DRV8825, and drivers with compatible pinout

Microstepping: configurable by jumpers, up to 1/16 (A4988) or 1/32 (DRV8825)

A axis: clone X, Y, or Z via jumpers, or independent control on D12 / D13

Limit switch connectors: 6 (X+, X-, Y+, Y-, Z+, Z-)

Spindle outputs: Enable, Direction

Coolant output: Coolant Enable

Control inputs: Abort, Hold, Resume, E-Stop

Motor connectors: 4 pins per axis

Compatible firmware: GRBL

Jumper configuration depending on the driver used:

Under each driver slot there are three jumpers (M0, M1, M2). In the table, 1 represents the presence of the jumper, and 0 its absence.

Jumpers are NOT included in the package.

Note: the markings on the board correspond to GRBL 0.8. In GRBL 0.9 and 1.1, with variable spindle speed enabled by default, the Z-axis limit switch is connected to the pin marked SpnEn (D12). The PWM signal for the spindle or laser is taken from the pins marked Z+ / Z- (D11).

Usage:

Download the GRBL archive and unzip it. In Arduino IDE choose Sketch > Include Library > Add .ZIP Library and select the grbl folder inside the unzipped archive.

Open File > Examples > grbl > grblUpload and upload it to the Arduino UNO board.

Set the microstepping jumpers under each slot according to the table above, depending on the driver and the desired resolution.

Mount the shield on top of the Arduino UNO board, making sure all pins are inserted correctly into the connectors.

Install the drivers with the correct orientation: the EN pin on the shield must match the Enable pin on the driver. Installing them backwards will destroy the driver and may damage the shield.

Mount the heatsinks on the driver chips.

If you use the A axis for cloning, place the jumpers on the STEP and DIR positions of the axis you want to duplicate (X, Y, or Z).

Connect the stepper motors to the 4-pin connectors, respecting the coil pairs (1A-1B and 2A-2B). If a motor rotates in the wrong direction, rotate the connector 180 degrees or reverse the direction in the $3 setting.

Connect the limit switches between the signal pin and GND. GRBL uses internal pull-up resistors, so normally open (NO) contacts work without additional components. For the Z axis, use the SpnEn pin (D12) in GRBL 0.9 and 1.1.

Connect the 12 - 36V DC power supply to the screw terminal, observing polarity. With A4988 drivers, do not exceed 35V.

With power on, adjust the current of each driver using the potentiometer on the driver (Vref voltage). Use the formula from the driver documentation and the motor's rated current.

Connect the Arduino board to the PC via USB and open GRBLcontrol or another GRBL control program, at 115200 baud.

Configure the number of steps per millimeter ($100, $101, $102), maximum speeds ($110 - $112), and accelerations ($120 - $122) according to the machine mechanics.

Test the movement of each axis with manual jog commands, without the tool installed.

For laser engravers with GRBL 1.1, enable laser mode with $32=1 and connect the laser control to the PWM output (pins marked Z+ / Z-, D11).

Attention: do not connect or disconnect the motors or drivers while the shield is powered, as the drivers may be destroyed instantly.

Notes:

To build a CNC with this shield, we recommend using the GRBL code available in the following tutorial: Uno and CNC Shield CNC tutorial

GitHub code: GRBL code in .zip format for Arduino IDE

CNC milling machine control software for PC: GRBLcontrol

Laser CNC control software: GRBL Laser