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

Friday, 27 December 2013

axCut WIP - X/Y axes and optics nearly complete

First spool of plastic down, and the mechanical elements of the x/y axes are virtually complete, as are the various brackets for the optics (mirror and laser holders).  

Steps to get x/y finished:
  • Design/print limit switch brackets (for microswitches)
  • Tweak and re-print x-carriage plate - holes for the v-groove wheel bolts are too tight, preventing correct alignment/pressure on the rails.
  • Finish design of cable-chain for y-carriage (have a basic design started, needs refinement)
  • Wire it up to RAMPS board - test!

Steps to get optics finished:
  • Re-design/print fixed mirror holder - current design is not sufficiently rigid; allows for some flex/vibration of the mirror
  • Fit laser tube (already tested, brackets work well)
  • Fit and align mirrors
  • Sort out water cooling (big-ish job!)
  • Wire it up, test it!

 Will do another post about some of the 20x20 fixings I've developed along the way, you can see some of them in the pictures above:

  • Printed nut carrier (inspired by: - used extensively, must have made over 200 of these by now!
  • Drop-in square nut carrier (for when you forget to insert a t-nut carrier and can't be bothered to dismantle the frame to slide one in!) - this is still WIP, as the current design is a right pain to use
  • Snap-fitting - these do not require a t-nut (or equiv), they push into the 20x20 slot and then tighten into place with an M4 screw (you can see these on the photo of the ATX PSU brackets)

After the above, it's on to assembling the bed and associated z-axes drives.

Saturday, 16 November 2013

Laser Cutter Build

Early days, but I'm currently spending a LOT of hours on a laser cutter build - heavily inspired by BuildLog 2.x and Lasersaur.  All of the design is in OpenSCAD, building on the excellent work by nophead on the Mendel90 - many of the vitamins are reused, with new vitamin libraries for:
  • Aluminium Extrusions (Bosch Rexroth 20x20 profiles) and fittings (e.g. gussets)
  • Openrail, and associated plates, V-groove wheels, etc
  • Laser Optics (tube, mirrors, laser head)
The project is on github:

Clone the repository and open axCut.scad in the latest version of OpenSCAD to view the WIP design.

Here's some of the latest images:

The first real parts arrived this week - a 40W laser tube, power supply and optics set from China.  Will be testing this over the next week or two, once I've sorted out a water cooling arrangement.

Full BOM is on Google Drive and will be published once finalised.  Will also publish to thingiverse once the machine is built/tested.

My particular requirements list:
  • 40W CO2 laser (with space to upgrade to at least 80W - i.e accommodate a 1000mm tube with water cooling)
  • Bed size to accommodate A1 stock - design files use 850mm x 600mm with 30mm margin all round
  • Fully enclosed
  • Allow for pass-through (i.e. very long items)
  • Allow for high/tall items and "autofocus" via motorised bed (150+mm travel)
  • Have unobscured front access for loading/unloading parts
  • Bench-top design (may integrate a bench at a later date)
  • Side connections for extraction and cabling (i.e. power, usb)
  • Investigate using reprap s/w stack vs Mach3 - I'd really like to leverage as much as possible from the reprap community (e.g. modified sprinter firmware)
  • Budget target of £1500 (max £2000)