Dewallie 20W UV Laser Review

Dewallie was kind enough to contribute a 20W UV laser for us to review and test out. It’s the LA-2 version of the machine with a head rated for 3.8A @ 5V using Pulse Width Modulation (PWM) power control. It’s got a large work envelope of 400mm x 400mm which puts it over twice the size of the popular K40 CO2 lasers (200mm x 300mm). Opening up the package and it’s been broken down into just a few pieces for shipping with a 5 step assembly process:

Mostly assembled out of the box.
The majority of the gantry comes preassembled with the X axis requiring no work at all
Fully assembled by someone with no experience in about 30 minutes

If you have a 3D printer this controller is going to look pretty familiar:

I bet you can drop an additional stepper driver on the open header but you’d still need to reflash the firmware. This looks like a pretty run of the mill GRBL Atmel 3 axis driver board but you’d need firmware or to reverse engineer the pinout to let you install a router motor and run it as a desktop router with a powered Z axis.

The easiest way for us to exhaust the laser was to put it inside our large CO2 laser, you’ll want to build a downdraft table or some form of fume extraction.

Once we had the machine constructed we needed to set up some better shielding. The machine comes with OD3 glasses, which when coupled with the nozzle/air assist cone they’re supposed to provide adequate reduction in brightness but we wanted to fully enclose the laser and provide a viewing window. $17 and an order to J Tech Photonics and we had a 12″ window with OD3+ protection to keep us a little better protected. It makes a world of difference in brightness:

Factory provided shield but you can see the amount of (bright!) indirect light leakage. They provide laser safety glasses but we wanted something that was easier to use/keep in place.
With the OD3+ acrylic window in place

Onwards to some test engraves and cuts. To frame expectations this is a 20W 445nm laser, it’s not going to cut like our 150W CO2 laser but it carries a correspondingly lower price tag and a minimal set of additional equipment required (no chiller/water cooling, multiple power supplies, etc). The machine does well running slowly (<10mm/sec for wiggle free vector cutting and engraving) and will need multiple passes to cut through plywood. Their sample materials give you a quick sense of what to expect: anodized aluminum tags and sheets for engraving, cardboard/tagboard, 2mm plywood, etc.

To start off make sure you test and set the focus. An easy way to visualize the focus height is to put a piece of thin wood under the laser and prop up one end to form a ramp. Have the machine cut a line and you can see where the laser is in focus based on how small the line gets:

The right side of the cut was closest to the laser output, you can see how the beam widens as it goes left showing that it’s losing focus.

The thin sample plywood they provide cuts and engraves well:

Provided 3 layer 2mm plywood cut well.

We had some thicker 3mm interior/cabinetry plywood that it had a hard time cutting through:

It knocks out about 0.75mm per pass at 90% power running at 5mm/sec
Reducing speed doesn’t seem to be a good strategy, it results in a lot more char/burning then taking many small bites.

It performs very well at engraving anodized materials:

The filled areas came out nicely, to demonstrate some issues you’ll see shortly I left high speed line engraving turned on and you can see the gantry has a lot of flexibility/wiggle at speed resulting in poor quality vector engraving. The resonance seems to be mainly in the Y axis which is what we’d expect there’s a lot of mass we’re hauling around in the X axis that results in belt flex. Cranking up the belt tightness and putting in gusseting/stiffeners would help here.
Take a look at the arrows below to get a better sense of the issue, you can see at 20mm/s the paper shows the resonance but when dropped to 10mm/s it’s almost totally gone, paper is a great way to visualize this because it’s cuts so easily.

Where these lasers excel is at raster engraving things

The 40mm/s 50% power engraving came out clean and consistent, no stepping from engraving in both directions at all. It looks a little blurry but that’s camera focal plane.

Where performance falls off is engraving at high speed (>80mm/s) detailed objects. The onboard controller is an Atmel microcontroller (Arduino) so the command rate is limited. I’m sure the laser can fire quickly but the controller isn’t up to the task like a much more expensive Digital Signal Processing (DSP) laser controller. Admittedly the DSP controller would cost you more than this entire laser so its far from an apples to apples comparison but it’s worth mentioning:

At left is a grayscale PWM engraved koi pond image from our 150W CO2 laser in a single pass, at right is an attempt at the same file on the UV laser at about 1/3 of the speed.

Where we had some fun was taking advantage of the small spot size and wavelength to cut 0.001″ steel shim stock. It is possible to cut steel but not mark it without dying the surface to improve absorption.

80% power 5mm/sec cutting through 0.001″ steel shim stock

It was able to mark Sharpie coated steel as well, the black pigment increases beam absorption and assists in the heat transfer rather than reflection.

Sharpie allows the beam to be absorbed into the surface rather than reflected, we were unable to pierce 0.002″ thickness material though so it’s very limited in capacity.
After cleaning the Sharpie dye off with acetone, also interesting is the heat affected zone retaining dye at the perimeter of the upper cut. It looks like the Sharpie can take a heat set and more readily resist solvents.

Overall for $310 you won’t find a much more capable machine, the 400mm gantry gives you a large work surface and it’d be possible to run this machine off a battery and do some outdoor/portable engraving since there’s little to bring along besides a laptop and the gantry itself. The downside with the 445nm UV laser wavelength is the heightened eye hazard working in a visible light frequency that can go through glass/glasses/corneas to damage your retina permanently – be careful!

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