A few month ago I acquired a KKMoon K4 3W miniature desk-top laser-cutter and it has proven to be a useful investment. Therefore, I would like to share a few operational insights, though you can find a variety of ‘test’ videos and the like on the Internet.
As with many Chinese products of this kind, it comes in various guises and configurations that may be mechanically identical or not. The traders’ descriptions are often somewhat haphazard and also suffer from translation issues. I am not sure, whether KKMoon is a trader or a manufacturer, their Web-site does not actually list these laser-cutters.
Prices between the different offers on the Internet marketing platforms can vary as much as 30%. However, I paid just over 100€, shipping included.

Image of the laser-cutter as advertised

The stated main specification of the machine I bought are

- Size: about 155 mm x 166 mm x 143mm
- Weight: ca. 600 g
- Laser Power: 3 W (3000 mW) – blue = xxx nm wavelength
- Engraving Area: about 80 mm x 80 mm (3.1" x 3.1")
- Engraving Depth: about 1 mm /0.04" (Adjustable in the range of 0-1 mm)
- Mechanical resolution: 0.05 mm = 512 dpi
- Supporting System: for Windows XP / 7/8/10 and MacOS 10.10 and higher
- Supporting Image Format: JPEG / JPG / PNG / BMP
- Connectivity: Micro USB B to USB A (cable included)
- Frame Material: ABS

The laser-cutting system consists of three main components that determine its capabilities: the mechanics, the control board, and the software.

Mechanics

The mechanical resolution of 512 dpi is not that brilliant, if you compare this with modern scanners or printers, but then mechanics have their price.
The 3 W diode laser has an adjustable focal point.

Control Board

I know next to nothing about electronics and commercial products, such as the control board that is being used in this machine. It would be particularly interesting to know, whether the board could be driven by other types of software. Perhaps someone from the Forum community has insights into this.

Driver

The software consists of two components, the driver and the cutting software itself. The driver is a standard piece of software under MS Windows and either comes with your MS Windows configuration or can be downloaded from the software producer’s Web-site. The driver runs under MS Windows XP/7/8/10. I am using an oldish mini-laptop with MS Windows XP on it. The driver unfortunately does not run under MS Windows emulation Parallels under MacOS 10.7.1, nor under the iOS for the iPad pro. The cutting software, however, seems to run in Parallels under MacOS 10.7.1. It should also run under MacOS 10.10 and higher, but I could not test this.

Cutting software

The cutting software is a very simple piece and is based on bit-image processing. In other words, the image is processed line by line from the top down and whenever a black pixel is encountered, the laser flashes. As noted above, the software can handle JPEG-, JPG-, PNG-, and BMP-files, but not TIFF. Images of up 1600 x 1600 pixels can be processed.
There are three variables that can be adjusted to control the cutting process: the laser power in %, the cutting depth in 0.01 mm increments, and contrast (0 to 256). It is obvious, what the power adjustment does and I assume the cutting depth is determined by the length of the laser pulse. The cutting speed cannot be adjusted explicitly. What influence the contrast setting has is not completely clear to me, as the screen appearance of the image changes, even when I use a 0/1 b/w bit image. In practice, however, it does change the width of the cutting traces.
The image to be cut can be freely moved around the cutting area of 80 mm x 80 mm on the screen.

Screenshot of the cutting software user interface

Set-up

The machine is mobile and in principle does not require any special set-up apart from a flat surface. However, any energy penetrating the material cut will be taken up by the surface on which the machine stands. This means that the material has to be fire-proof. I happened to have a piece of roof-slate at hand, which turned out to be very useful for the purpose. Pieces of marble or tiles would do as well.
The laser beam needs to be focused onto the material to be cut. The machine comes with a piece of black cardboard for the purpose, but this is thicker than many of the materials to be cut. It is better to focus the beam on the material in question. The laser spot is very bright, making it difficult to see, whether its size is minimal. I found it useful to illuminate the cutting area with a strong table lamp so that the contrast is reduced during focus setting.
The material to be cut needs to lie absolutely flat. I have been thinking of making some clamping rails or similar. It turned out that short tabs of cellotape are quite sufficient for the purpose. The small pieces of material are just taped down at each corner onto the slate.

Cutting times

I did not make systematic tests, but the examples shown here took about 10 minutes to cut. I would estimate that covering the full 80 mm x 80 mm cutting area would take in the order of about one hour.

Steering wheels cut from 0.15 mm thick Canson paper (120 g/m²) (cutting area about 40 mm x 40 mm)

Capabilities

Whether a material can be cut by laser depends on a number of properties of the material in question. First of all the material must be either combustible or it must be able to be evaporated. The material must be capable to absorb enough energy to reach its combustion point or its evaporation temperature. Whether a material can absorb enough energy depends in turn on a number of factors.
A key factor is its albedo, in other words, how well the material reflects or absorbs light. Bright and shiny materials reflect most of the light, as do white and light coloured materials. Hence they are not absorbing enough energy. Conversely, dark and in particular black materials absorb most of the light that is shot at them.
Another factor that determines how much energy is needed to combust or evaporate it is its volumetric density. Compact materials with no pores contain more mass per volume than porous materials and hence need more energy per volume to combust or evaporate. The volumetric heat conductivity is also important. If the material conducts heat well, the energy transmitted may become dissipated before it reaches the flash-point or the boiling-point.
While in theory virtually all materials could be cut with a laser, in practice the available laser may just not be powerful enough.

In practical terms this means that it is not possible to cut metal and transparent or translucent materials with this small laser. The 3 W laser just does not impart sufficient energy to melt and evaporate metals. Not surprising though. Plexiglas or tracing paper let all or too much of the light pass and therefore cannot be cut.

Bakelite paper has a high evaporation temperature and is translucent. It can be cut through in thicknesses of up to 0.1 mm, but edges become charred. A strategy can be to only cut part through and then brake off the part along the cutting. This works only for simple shapes with straight edges and not too small parts.

As set of doors (ca. 11 mm high) cut from 0.1 mm bakelite paper


White polystyrene is too reflective and is only lightly engraved, if at all. I did not have black polystyrene at hand to try this out.

I would abstain from cutting PVC due to the generation of toxic and corrosive combustion products.

I have not tried ABS or Lexan, but would expect similar issues as for polystyrene.

Celluloid might cut well, if you have a coloured variety. Transparent celluloid, including drafting films such as Ultraphane, will not work. The high flammability of celluloid may be an issue.
 
White paper works moderately well due to its high reflectivity. An important factor is also its weighing and seizing. Weighing with barite or titanium oxide makes it more difficult to cut, as both materials are refractory. A seizing with glue or plastic polymers increases the volumetric density and therefore make the paper more difficult to cut.

Coloured papers and cardboard work best, but thicknesses above 0.5 mm become more difficult to cut. The deeper the cut the more charring of the edges will occur, loosing precision in size and reducing the minimum size of features that can be cut.

I have not had the opportunity to cut wood, but I would expect that low-density woods cut better and then hardwoods. The size limitations are likely to be similar to those of cardboard.

Cork should cut reasonably well, but I have not tried it myself.

Drafting for cutting

As for any other ‘machining’ operation, the ‘tool’ diameter is an important consideration. The effective diameter of the well-focused laser-beam is in the order of 0.1 mm. These leads to the rounding of internal corners in this order of magnitude, but the actual rounding depends also on the size of the opening to be cut. Smaller openings may have a more perceptible rounding than larger ones.
In practice, the charring of the edges leads to slightly larger openings than those drawn. Thus the diameter of e.g. holes needs to be drawn 0.1 mm less than required. Similarly, slots should be chosen 0.1 mm narrower than the nominal width.
The laser sends a pulse for each black pixel encountered. When converting vector drawings into bit images, the question arises of the actual size of the parts that appear white in the final image to be used in the laser-cutter. This may depend on the line thickness chosen and the kind of drafting program. I found that I needed to experiment with the cutting parameters (power setting and contrast) and in some cases needed to redraft (parts of) the drawings in order to arrive at the correct size. Several iterations may be needed to arrive at the correct size. This also depends on the material, thicker material requiring more adjustments.
Every part that is black in the drawing will be burned. In order to reduce the laser time and the fumes generated, it is good practice to fill in any empty space. While this would be good practice in photo-etching too in order to safe etching fluid, often this is not done. However, when converting drawings for laser-cutting it is a good idea to fill in the empty spaces.
I use a 2D CAD system for drafting (EazyDraw™). This program allows the drawing to be exported into picture formats such as JPG. The resolution for this step has to be chosen so that the final part has the correct size for a resolution of 512 dpi or 202 pixels per centimetre. This means that a part that is 1 cm long should be 202 pixels wide in the JPG etc. file. In order to reduce the area to be burned, I usually import the image into Adobe Photoshop Elements™ and whiten all the respective areas. Sometimes is also convenient to draw the parts in solid black, which then necessitates their inversion in Photoshop. I typically export the drawings at 1024 dpi and then reduce the image in Photoshop to the desired width in the number of pixels as calculated for 512 dpi after the post-processing has been done. This allows me to ascertain that the drawing has the desired size. In this way it is also easy to produce cutting designs in various scales from the original drawing.
As the cutting happens on a flat surface and there is no mechanical interaction with the material, the cut pieces do not move from their place during the cutting process. Therefore, retaining tabs, as you would need in photo-etching, are not needed and the parts can be completely cut out. This avoids the problem of distortion during separation from the fret, particularly of very small parts.

A typical JPG-image as used for the cutting process (size around 35 mm x 30 mm)

Safety

Lasers are dangerous for the eyes and you are advised to consult the respective guidance on laser safety.
The laser-cutter comes with a green protective glass on one side. I also bought a pair of green safety-glasses for adjusting the laser focus, as viewing the focal point through the shielding glass is inconvenient.
The combustion fumes of certain materials can be a nuisance, noxious, or carcinogenic. In any case they are smelly. As noted above, it is wise to reduce the areas to be burned in order to minimise the amount of combustion products. For certain materials some kind of forced aeration may be needed, or you need to set up the laser-cutter outside.
Some materials may also be a fire hazard. However, none of the materials I worked with seem to have been problematic in this sense. There would not be enough mass to sustain a serious fire, but a fire-proof base is important.
In any case: never leave the machine running unobserved !

On the Internet you can see people, who have encased their cutters and added forced ventilation to it. Whether such arrangement is warranted, depends really on how intensively you use it. In my case it just runs occasionally for a few minutes at a time.

Conclusions

This technique cannot fully replace photo-etching to produce small, complex and delicate parts, but is is a versatile ad hoc option requiring little preparation in comparison. The cost of materials is minimal and therefore that of trial and error. There are no chemicals to manage safely, but fumes can be an issue.
There is no equivalent to the ‘surface etching’ process, parts are strictly two-dimensional. As in photo-etching, there is, however, the possibility to build up parts from several layers.
Metal surfaces and its edges can be made very smooth. Achieving the same effect with paper or cardboard is difficult, even when treated with wood-filler to produce some sort of compound material that can be sanded. In some applications that surface roughness does not matter or may be even desirable.
The mechanical resolution of 512 dpi and the diameter of 0.1 mm of the laser-beam impose limitations to the minimum size of parts that can be produced. Laser-cutting with such small desk-top machine cannot compete with commercial etching processes using high-resolution masks.
In scratch-building, when parts need to be developed as the building goes on this kind of laser-cutting certainly is a useful ad hoc and flexible process.