Thursday, 16 January 2014

axCut Laser Cutter - cracked it! z axes working, honeycomb bed installed - lovely jubbly!

Have finished installing the z-axes drives along with the honeycomb bed, and it has made such a difference.  I've been able to run some test cuts and finely calibrate the focal point (to within 0.1mm).  The host comms also seems to be behaving better (I'm convinced it's my windows laptop causing issues).

So... here's a video of it all working together - and it is working extremely well.  The test cut in the video is based on a friends wedding invite, and has converted into just 2223 lines of gcode - nice and compact thanks to the bezier curves!

The finished cut is very, very good - comparing it to the commercial reference (from same design file) it's as good, if not better (less wobble to the edges).  The low feedrate I've used may also be a contributing factor, but I'm still feeling rather smug.

Still lots to do on the hardware side (enclosure, cable chain for air assist, a rigid trolley), but for now, I think I'll take some time to play with cutting stuff!

Monday, 13 January 2014

axCut Laser Cutter - first cuts; not quite epic fail

We have cutting!  and a lot of smoke - really must order the cladding and setup some extraction!  This is a proper "Tomorrows World" video, it doesn't quite go to plan, but nonetheless - there's definite progress:

The cutting paths were generated from SVG via a little converter program I wrote using the paper.js library.  The arduino/Marlin combo is processing the bezier curves (as demo'd in previous video), but now with the addition of laser on/off commands around each path.  Air assist working nicely, except when the airline is being burnt by the laser :(

Laser control and watercooling all working well - the watercooling pump runs continuously, but the radiator fans only kick in when the laser outlet water temp rises above 22 degrees C.  The watercooling system is very quiet, thanks to the excellent little pump (Phobya DC12-260).  The fans are also extremely quiet when they are running, but the water temps haven't gotten above 19 degrees as yet (ambient temp during testing was just under 18, thanks to doors/windows being open for the smoke).

Laser control commands include arm/disarm of the laser PSU, control of laser power (0-100%), laser on/off and a diagnostic output.  The laser power control is via high speed PWM (62KHz, using timer4).
Air assist will soon be integrated into the relay module, so it can controlled by the arduino (via a couple of G-codes).

Air assist clearly plays a big role in:
 - stopping fires!  (without the air assist, there's a persistent flame about the cutting point)
 - keeping crap away from the lens

I'm assuming cut quality will get much better once the honeycomb bed is installed (so smoke/heat isn't being contained under the work) and once the focal point is properly calibrated.  I did go on to adjust the bed and do some power/feedrate tests, some of which you can see in the video below.  After bed adjustment, the cutting kerf at optimal power/feedrate is approx 0.2mm... should still be able to get better than that.  There is also quite a bit of scorching around the cut line, hoping the honeycomb+air will dramatically reduce that.

 - Order cladding
 - Install honeycomb bed
 - Finish wiring z axis
 - Calibrate focal point
 - Solve raft of pronsole errors when sending complex jobs - presumably some errors in my firmware extensions
 - Integrate air assist line into axes (i.e. an x-axis cable chain)
 - Design/order/build decent trolley

Wednesday, 8 January 2014

laser cutter references

other than BuildLog and Lasersaur main sites.... I've also borrowed/been inspired by several items from Daniel's blog:

In particular, I've borrowed the design of my laser tube mounts and plan to implement something along these lines for the diode laser:

I like the passive design (dropped into the beam by the lid opening), but I'd also like to be able to use the visible pointer with the lid closed - so I'm thinking a little servo to lower the diode and a s/w interlock to ensure the laser can't activate if the diode is down (maybe not the safest arrangement, but hopefully good enough).

axCut Laser Cutter - Y dual stepper homing and z axis drives

Have uploaded a quick overview video of the completed homing system for the dual Y stepper arrangement:

It uses a normal microswitch on one side (the Y2 side) and a linear hall effect sensor on the other (Y side).  Have updated my fork of the Marlin firmware to support this homing technique.  Calibration parameter is modified using M666 command (and M667 to read), values stored in EEPROM.

Homing algorithm:

  1. Home Y as per normal
  2. Disable Y2 stepper, disable endstops
  3. Measure hall reading and compare to calibration target
  4. If error big, move Y one step towards correct position and goto 3
  5. Enable Y2 stepper, enable endstops
I'm currently using 32x oversampling on the hall reading, with 5ms delay between reads, but there's still a load of sensor noise.  Doesn't help that the sensor is next to two stepper motors!  Works ok, just takes a few iterations to converge.  Will do for now.

Z axis drives fitted (uses Mendel90 z-couplings) and ready for wiring tonight.

Sunday, 5 January 2014

axCut Laser Cutter - X/Y axes working, laser calibrated

Now have both the X and Y axes working and have calibrated the optics using a mock tube to hold a visible laser diode.  The laser calibration technique may be of interest to others building laser cutters, as it means I can carefully calibrate the optics with the visible laser, then drop in the CO2 laser and be fairly confident the beam will follow the same path - will found how well this works in a few days when I fit and fire the CO2 laser!

and a quick demo of high feedrate with a lissajous pattern:

Up next:

  • Finish the water cooling system
  • Integrate the laser power supply
  • Fit and test fire the CO2 laser
  • Finish the z-axes (waiting for stepper motors to arrive)
  • Add RPI host controller and touch screen
  • Order cladding