Our lasercutter is modified from the Buildlog.net 2.x 40W Laser Cutter design. Its outer dimensions have been lengthened from the original 600mm to approximately 900mm. It uses a RepRap RAMPS 1.4 motherboard, which incorporates stepper drivers. It makes use of an 18mm ZnSe focus lens with 55mm focal length.

Z axis travel is 98mm (software limited to 95mm) from home switch to air nozzle tip. The workpiece should be approximately 13mm from the tip of the air nozzle when cutting.

• Download the inkscape template file here. If you don't use the template file, it's important to set all document units to millimeters.
• Open it in inkscape and draw the object you'd like to cut
  • Save the drawing to SVG or PDF
  • Upload the drawing to Laser Beta
  • Download the generated G Code file
• Or
  • Use this plugin to generate gcode in inkscape: https://github.com/ajfoul/thlaser-inkscape-plugin/tree/master
• Load the G Code file in Pronterface, or onto an SD card
• Cut!

Firmware is on github, here: buildlog-lasercutter-marlin

The laser is controlled by sending commands (“g codes”) to it via USB→serial connection. Additionally, the laser control electronics can read files containing these commands from an inserted SD card without the aid of an attached computer.

There are several ways to command the laser to fire, each is enabled or disabled at compile time, according to the following option in Configuration.h:

• LASER_FIRE_G1 (default: on): G0 moves the laser to a specified set of coordinates without firing, a G1 command moves the laser to the specified coordinates while firing.

• LASER_FIRE_SPINDLE (default: on): M3 turns the laser on in place, without requiring it to move. M5 turns the laser off in place.

• LASER_FIRE_E (default: off): Any movement in the E axis (which represents the extruder when controlling a 3D printer) fires the laser. In this way, the laser can make use of unmodified g code generated for 3D printers.

Each of these firing controls accepts the following parameters, which can also be manipulated without firing or moving the laser by using them with the M649 command:

  ; Moves to (5, 6, 7) at speed 8, laser off
  G0 X5 Y6 Z7 F8
  
  ; Moves to (5, 6, 7) at speed 8, laser pulsing 1.2 times per millimeter, for 50ms, at 60% power, with serial diagnostics messages, in Pulsed mode.
  G1 X5 Y6 Z7 F8 P1.2 L50000 S60 D1 B1
  
  ; Without moving in any axis, pulse the laser for 50ms at 60% power, with serial diagnostics messages, in Continuous mode.
  M3 L50000 S60 D1 B0
  
  ; Without moving in any axis, turn the laser off.
  M5
  
  ; Without moving in any axis or turning the laser on or off, set the laser power to 50%, pulse length to 60ms, pulses per millimeter to 1.2, in Pulsed mode, without serial diagnostics.
  M649 S50.0 L60000 P1.2 B1 D0
  ----------------------------
  S: intensity (0.0-100.0)
  L: duration (microseconds)
  P: pulses per mm
  D: diagnostics (0 = off, 1 = on)
  B: laser firing mode (0 = continuous, 1 = pulsed, 2 = raster)

In Continuous mode, the laser is turned on, and remains on at the selected intensity until it's instructed to turn off.

Pulsed mode fires punctuated bursts at intervals matching P: PULSES_PER_MM, each lasting for L: DURATION. That gives us all the information we need to time the laser firing and extinguishing from the inner loop of the stepper driver interrupt handler - the core of the firmware. This makes the positioning and timing of pulses in Pulsed mode much more accurate than any other method. Pulse positions are accurate to the nearest step in any axis and reliable minimum pulse times of 250 microseconds have been measured on a 16Mhz Atmega 2560 (better may be possible, but hasn't been tested). Stock Marlin's minimum pulse length is 8.2 milliseconds on the same hardware, and permits adjustments no smaller than 1 millisecond.

Raster mode is a special variation of Pulsed mode which allows you to specify a unique intensity for each pulse in a variable-length horizontal line of evenly spaced pulses, with configurable 'pixel' size and aspect ratio, arbitrary line-advance, and selectable left or right blitting. This is everything required for maximally efficient arbitrarily large 2D image blitting, but allows for a number of other uses as well. An obvious improvement would be to allow for Raster blitting along an arbitrary line in 3D space - patches welcome! Because pulse timing can be done in the stepper driver interrupt handler, and the information necessary for many pulses is contained in a single command, Raster mode is very fast. Raster mode only works with the “G7” command which accepts a number of unique parameters:

  G7 N0 L68 DAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAhaGBUQFRiZ0ZPVExARUU6RTpITD1GU05Q
  -------------------------------------------------------------------------------
  N: new line: increments Y axis by LASER_RASTER_MM_PER_PULSE * LASER_RASTER_ASPECT_RATIO from Configuration.h 0 = negative movement in the X axis, 1 = positive X axis movement.
  L: byte length of the packed pixel set
  D: data, base 64 encoded 0-255/pixel

In firmware, you have two options for controlling a laser:

1. Single pin: The LASER_FIRE pin supplies a PWM signal at at Hz specified as LASER_PWM in Configuration.h, adjusting duty cycle of the wave to control intensity, and supplies logic level LOW when off. Common for laser diode

  Wiring diagram:
  
  -------
  | G   |  ----  Ground
  | TTL |  ----  LASER_INTENSITY
  -------

1. Two pin: The LASER_FIRE pin supplies a logic level signal HIGH for fire, LOW for extinguish. The LASER_INTENSITY pin supplies a PWM signal at at Hz specified as LASER_PWM in Configuration.h, adjusting duty cycle of the wave to control intensity.

  Wiring diagram:
  
  ------
  | H  |  ----  LASER_FIRE
  | L  |
  | WP |
  | G  |  ----  Ground
  | I  |  ----  LASER_INTENSITY
  | 5V |
  ------

laser.cpp contains the laser_fire and laser_extinguish functions

This firmware also has options to control peripherals of a laser cutter such as the air assist, water pump or even idle shut off via a slave arduino.

Many of the laser cutter's components were purchased from LightObject.

• Power Supply Manual
• The laser cutter electronics consist of an Arduino Mega 2560 and RAMPS 1.4 shield.
• Peripheral control relay board: http://yourduino.com/sunshop2/index.php?l=product_detail&p=201

• http://www.laserbits.com/

• http://learn.adafruit.com/laser-custom-stamps/printing

• Power off the laser cutter
• Move the Y axis carriage to the rear of the laser cutter
• Loosen the bolt mounting the Y belt idler bracket to the frame, pull the bracket toward the front of the machine to tighten the belt, while tightening the mounting bolt to secure the bracket in place.
• Repeat procedure for the second Y axis belt.

• Loosen the bolt mounting the X belt idler bracket to the gantry, pull the bracket toward the left side of the machine to tighten the belt while tightening the mounting bolt to secure the bracket in place.

• Cut zip ties holding material support grid
• Remove the grid from the laser cutter and set aside
• Loosen the Z axis belt tensioning bracket located at the rear of the machine
• Disengage the Z axis belt from each of the pulleys connected to the Z axis leadscrews
• Use the 8 inch digital calipers (found in the metal shop) to measure the distance between the Z axis leadscrew brackets on the lasercutter frame, and the paired bracket on the material support frame at each corner
• Adjust each leadscrew by hand
• Engage each pulley with the belt
• Adjust and re-tighten the Z axis belt tensioning bracket at the rear of the machine
• Re-install the material support grid

• Use the LCD to select “Laser Functions” then select “Material thickness” then select the thickness of your material. The Z axis will home, then move to the appropriate position to cut material of the specified thickness.

• http://wiki.linuxcnc.org/cgi-bin/wiki.pl?Simple_LinuxCNC_G-Code_Generators
• http://wiki.linuxcnc.org/cgi-bin/wiki.pl?Cam
• http://securetech-ns.ca/camm-linux.html
• http://www.inkscapecuttingdesign.com/index.php
• http://inkcut.sourceforge.net/
• http://www.shapeoko.com/wiki/index.php/Laser_Cutter
• http://www.instructables.com/id/How-to-Use-a-Laser-Cutter/
• http://wiki.thinkhaus.org/index.php?title=Laser_Cutter
• http://wiki.linuxcnc.org/cgi-bin/wiki.pl?Simple_EMC_G-Code_Generators
• http://wiki.fubarlabs.org/fubarwiki/Laser-Cutter-Inkscape-Setup-Notes.ashx

Brian Adams suggests that since we have a Z axis, we could extend the Z axis, which would entail a taller case and longer Z-axis leadscrews. This would permit things like the laser origami (see http://www.wired.com/design/2013/02/laser-origami/).

Sam's Laser FAQ

• Should we put filters on the air and water lines?
  • Panic button. Signal the motherboard to safely stop all motion.
• It would be nice to have sensors to detect low water levels in the reservoir, or restricted water, air, or exhaust flow. Also for excess beam power, or any other conditions that could damage the laser tube.
• We need limit switches or sensors so the lasercutter doesn't eat itself by trying to perform impossible motions.
• We need to write a step-by-step testing plan to make sure our safety features work. We should test safety mechanisms for repeatability and reliability. I do not want to lose my vision, nor set fire to the building.

YouTube video testing the laser cutter