Converting a 2418 Desktop CNC to Laser part 1

I had been toying with the idea of swapping the spindle motor for a laser on my 2418 desktop CNC machine. The Woodpecker 2.6 controller has a laser output which is straight ON/OFF but I wanted to use a 5.5 W PWM controlled 450 nm blue laser so that I could adjust the laser power on the fly. The Laser I found on line is made by WonVon and comes with a controller with 12V and TTL (PWM) inputs. The software I found is similar to the GRBL software I used for CNC work and is called LaserGRBL v3.1.2.  I believe what I found out will work for any PWM controller laser running any CNC/Laser type software using the GRBL controller.

I discovered that the Atmega 328 that is the brains on the Woodpecker is the same chip used on an Arduino. It had a boot loader called GRBL 0.9 but I needed to upgrade to 1.1 to be able to control a laser. There are a lot of instructions and discussions available showing how to do this on an Arduino but nothing clear for the Woodpecker. Fortunately, there is a utility built into LaserGRBL that flashes the 1.1 firmware (bootloader) with the push of a button. The USB interface to the Woodpecker uses a CH340 chip and LaserGRBL also has a utility to install the driver. Both utilities are in the menu bar under Tools.

I thought that the PWM pin that the S command (laser intensity) in G code was available on the 34 pin header. Sadly I was mistaken. The signal originates from the D11 pin on the Atmega 328. On the Woodpecker the 328 is too small to solder directly but D11 connects to the big power MOSFET that controls the spindle. You can see I soldered a short piece of blue solid 22 gauge wire directly to the MOSFET signal pin in the photo below. The brown ground wire is a female 0.1 jumper end. Both of these are spliced to the PWM input. White is PWM + and yellow is ground. The other connector in the photo with yellow and white wires connect to an external 12V DC power supply. On this connector yellow is + and white is ground.

I also thought it would be nice to easily switch between Laser and Spindle mode on the 2418. I hoped the spindle motor clamp was the right size to also hold the laser. Again, sadly I was mistaken. Fortunately I found that Brandon Piner had published some stl files on Hackaday that showed promise. His CNC Z Mount allows the easy exchange of tools. Brandon also put his files on Thingverse where a remix by wb-maker gave me a mount for my laser. Now all I needed was a mount for my spindle motor. I drew this out in Inventor and then got all three parts, the Z Mount, the laser mount and the spindle mount printed.

The next 3 photos show the Z Mount, the Z mount with the laser attached and the Z mount with the spindle mount attached.

In order to use the new Z mount I had to push the 4 bearings and lead screw adapter out of the original spindle mount and then push them back into the new Z mount. I was careful to use objects like bolts that were the same diameter as the bearing or adapter to gently tap them out/in. To push them out I supported the block on a solid surface with a hole large enough to receive the bearing or adapter. To push them in I made sure the parts had a thin coat of oil and were held square to the hole. No excessive force was needed.

In part 2 I will talk about getting the software set up and using LaserGRBL to do line art and grey scale bitmaps.