Computing stuff tied to the physical world

What’s in a laser cutter

In Hardware on Sep 18, 2012 at 00:01

Let me describe this thing I ended up with:

  • mechanics: the main part is a solid bright red metal box with a few compartments:
    1. left = X-Y table
    2. right = electronics
    3. back = laser tube
  • electronics: the LaOS main board and an ATmega168 as I2C-connected control panel
  • water reservoir + circulation pump, for cooling, must be on when the laser is on
  • air pump (noisy aquarium type) – for “air assist”, keeps the fumes away from the lens
  • exhaust ventilator, mounted on the back, pushes the smelly & smoky air out

The pumps and ventilator are manually turned on from the front panel with separate switches. Not perfect, since this leaves room or operator error, but hey – it works.

Here’s a peek inside, with some packaging plastic still in place:

DSC 3512

The shiny plate height can be adjusted using 4 connected screws turning in tandem.

You can see a little fluorescent light in the top center, and the air exhaust underneath it.

A 35 Watt infrared laser is serious stuff (it actually requires a few hundred Watt to generate that sort of power). Once focused, that beam can do major harm – cutting through stuff is what it’s supposed to do, after all.

Safety comes in the form of a reed relay which triggers when the lid of this thing is lifted (top right above), another one when the lid of the laser on the back is open, and a mains power switch with a key. The lid for the electronics is locked (from the X-Y compartment). The transparent viewing area is of a special type which blocks laser light, and the whole thing is made of fairly solid steel.

The beam is invisible (scary, eh?), but a tiny red “pointer” laser is mounted inside, showing roughly where the beam will hit. Extremely useful while doing dry runs – which in turn is very easy to do: just start the laser with the lid open, and you can see where it’s going to cut. Given that the cutting area is only about 20×30 cm, that’s not a luxury – you really have to check whether the material is properly placed. Here’s that last mirror, deflecting the beam down into the final focusing lens:

DSC 3489

(Note: that’s not smoke, but the red panel’s reflection on the aluminium work surface)

The hollow tube is the “air assist”, blowing air to push the smoke away from the beam.

All the mirrors come pre-aligned and secured with a bit of hot glue. No need to tweak.

On the side is that little pointer laser. Since it’s tilted, the position of the spot is not exactly where the laser will hit, depending on how far into the material you place the focus spot. Focusing is actually quite simple: the laser comes with a little (lasered) acrylic piece, the side of which has a specific length. To focus, you place that on the work piece, and then lower or raise the object until the plastic spacer aligns with this metal mirror mount.

Raising / lowering the work piece is done manually. The whole thing sits on a (fixed size) “honeycomb” bed, which in turns sits on a manually adjustable metal “table”. Adjustment is done with a screw sticking through the bottom of the laser – and in fact the very first thing you need to cut is a piece of wood to act as large adjustment ring, which can then be grabbed from the front of the laser. Bit hard to explain, but then again this isn’t meant as assembly instruction – I just want to give you an impression of what sort of issues you have to deal with in such a setup. On the plus side: pioneering is fun! – with lots of opportunities to come up with clever improvements :)

Tomorrow, I’ll describe the electronics. This board (and the software developed for it) replaces the original board, which I’m told was hard to use, came with crude Windows-specific software, and was impossible to hack on and improve. The LaOS board has a microntroller, two stepper motor drivers, an Ethernet port, and various other bits and bobs needed to deal with everything in the HPC laser. It’s actually quite general-purpose.

  1. Just a thought… Those mirrors, are they surface silvered or cheaper, traditional, back silvered?

    If the latter then you’ll be getting multiple reflections first from the air/glass interface and then from the glass silver (which you want), and then again from the glass/air as the beam comes back out again. This will happen on each mirror.

    • Yes, definitely surface (might actually be gold) – the double reflections would cause all sorts of problems. It’s probably this set: http://hpclaser.co.uk/index.php?main_page=product_info&cPath=2&products_id=8

      The lens is the one that sits right above the cutting area and it seems like it needs to be cleaned from time to time, due to fume residues probably. The only other serviceable part is the water-cooled glass laser itself, which presumably has a 1500..2000 hr lifetime (does it gradually lose power? no idea).

  2. In the photo I can see through the thickness of the mirror, so it is presumably a first-surface (front) mirror. I don’t think you can use 2nd-surface mirrors with high-power lasers.

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