The Maker's Manual: A Practical Guide to the New Industrial Revolution 1st Edition (2015)
Part III. From Bits to Atoms
Chapter 14. Laser Cutting
The last digital manufacturing technique we are going to consider is laser cutting. Nowadays, it seems like without a laser cutter, you can’t be a maker. Though we don’t necessarily agree with that assessment, we do agree that laser cutting is a very important tool in a maker’s toolbox.
Lasers
The word laser is an acronym for Light Amplification by Stimulated Emission of Radiation: big words that basically mean “watch out, this burns!”
A laser can direct a lot of power to a very small area, thereby melting, burning or even vaporizing the material we are working on (or enemy robots). Based on this principle, laser cutters have been created that are capable of working on a wide range of materials.
Laser Cutters
There are various kinds of laser cutting machines on the market, which differ in the variety of materials they can work with, their mechanics, their optics, the kind of laser, and other factors. The most commonly available laser cutters are based on the excitation of a gas, mainly carbon dioxide (CO2). Beside the optic system, which directs and focuses the infrared light emitted by the laser, an air or gas blast is used to clean the material from the debris generated by the laser cutting process.
On some cutters, the laser is fixed and the material moves, while on others the material stays in place and the laser beam moves. In most designs of this type, the laser tube remains stationary, and a series of movable mirrors convey the laser beam wherever needed. The mirrors move similar to inkjet printer heads, though on two axes instead of one, so this way they can cover an entire plane. When you come right down to it, a laser cutter is essentially a computer numerical control (CNC) machine, which reads instructions and guides the tool in its operation.
Figure 14-1. Laser cutting attendee badges to commemorate the first White House Maker Faire
A laser cutter can work with many materials: acrylic, paper and cardboard, wood, felt, fabric, rubber, leather, Plexiglas, and--if the machine is powerful enough--even some kinds of metal. The processing is also different: by adjusting power and focus it is possible to cut the material, score the material (for later cutting), or engrave the material (by writing or drawing on it).
Figure 14-2. Finely detailed laser-cut work by Larry Zagorsky of AS220 Labs in Providence, RI.
The standard thickness of the materials is a few millimeters, though there are machines which can cope with dozens of millimeters. This shouldn’t limit you to creating flat objects: you can design objects with cuts and joints that, when pieced together, create three dimensional objects, from simple boxes to more complex products.
Some software, such as Autodesk 123D Make, start from a 3D model to generate flat shapes that, properly put together, can create actual sculptures.
Figure 14-3. Makeropoly, Mark Plaga’s laser-cut homage to a classic board game from Maker Faire North Carolina.
Beside the many machines available on the market, projects are being started within communities, such as Lasersaur, an open source laser cutter. A machine of this kind is safe and powerful enough to meet the maker’s needs, at a reasonable cost. Moreover, it is documented in all its aspects, so if you wanted to change something you would just need to fork the initial project, clone the project documents repository, and use it as a starting point for your creation.
Even with open source alternatives, only few of us can afford a laser cutter, given the relatively high cost. Fortunately, there are many services that put the full power of a laser cutter at your disposal in a click, and at a reasonable price. As of this writing (early 2015), they are so ubiquitous that a Google search for “laser cutting service” should turn up quite a few companies in your area. Many of them offer high professional service and can help you in the modeling phase.
A laser cutter is one of the standard equipment tools of a Fab Lab and in many makerspaces and hackerspaces, so if you are lucky enough to live in a city where there is one, you can join that space or sometimes pay a small fee to learn how to use the laser and have access to it for your projects.
What’s The Use?
There are many things you can do with laser cutting:
§ a perfectly functioning steadycam, made out of 3D printed parts, ball bearings, gym counterweights and bicycle handles;
§ snap-together boxes, customized and engraved;
§ full-height plywood shapes resembling your friends;
§ gear that is not subject to much wearing or stress;
§ 3D objects, obtained by snapping together perpendicular sections or by layering parallel sheets;
§ sculpted books;
§ business cards;
§ necklaces, earrings, pendants, buttons, bangles;
§ inscriptions or graphics engraved on different materials;
§ artistic objects.
Models
The model needed for laser cutting is basically a vector graphic in two dimensions, where the color of its lines refers to specific processing. The laser cutting software will translate this model into instruction that the machine can understand for the actual cutting process.
Vector Graphics
When you look at pictures taken with a smartphone, you are looking at a bitmap or raster image, which are made of millions of tiny dots called pixels, each set to a different color.
When you use vector graphic software, you represent very complex shapes through mathematical relationships, just as you can draw a circle by knowing its center and radius. In a vector image, the software calculates the position of each pixel, based on the different formulae in the image file. Vector graphics can be more complicated, but they’re also precise.
For the preparation of laser cut models, any vector graphic tool can be used, for example Adobe Illustrator or CorelDRAW. You could also use Inkscape, a much less expensive tool (it is free!), which we’ll describe next.
Inkscape
Download Inkscape from the official website, follow the instructions for installing it on your operating system, then run it. Inkscape is user friendly; among other things, it features a series of tutorials which guide you step-by-step in making something, even if you have never seen--let alone used--vector graphic software. Tutorials are designed to help you learn by trying, in perfect maker spirit: there are no complex and boring texts, just Inkscape files, which you can modify directly to understand how to use the different tools.
To open the tutorials, click Help on the menu, then highlight Tutorials: the system will show a list of available files. Open the first one, Inkscape: Basic. The first part of the tutorial explains how to move within the document, how to zoom it in or out, create a new file, or edit an existing one. The default Inkscape file format is SVG (Figure 14-4) , which stands for Scalable Vector Graphics, a widely supported, standardized, and open format. SVG is based on XML, a text format, so Git ( Chapter 10) can help you keep track of the changes in your designs over time.
The circle definition looks like this:
<path
sodipodi:type="arc"
style="fill:#fe5b58;fill-opacity:1;stroke:none"
id="path2985"
sodipodi:cx="151.42857"
sodipodi:cy="295.21933"
sodipodi:rx="271.42856"
sodipodi:ry="277.14285" >
Figure 14-4. A circle and its SVG representation.
The tutorial guides you gradually while you create rectangles, stars, spirals, and other shapes. After playing with the tutorial for a while (we recommend the first two, at least) let’s move on to the design of a mini-project: a little sign with a couple of logos and some writing. Create a new document, and save it to a new folder/directory, which we’ll refer to as the working directory of the project. Make sure to save as an uncompressed SVG, so that git can show you differences later on.
Our logo (Figure 14-5) is made out of two images and two separate texts. Let’s start with the text: click the Text button or press F8 in Inkscape. Click anywhere in the document--you’ll have time to find the right positioning for the writing later--and start typing, as shown in Figure 14-6.
Figure 14-5. The logo we want to transfer from the bits to the atoms world.
Figure 14-6. I am not a Frankenstein. I am a Fronkensteen!
To change the font, select the text and click the drop-down menu at the top left, then choose a font as shown in Figure 14-7.
Figure 14-7. Selecting a font for the text.
Through the other buttons of the toolbar available to you when using the Text tool (Figure 14-8), you can further edit the text style, for example by changing character size and spacing.
Figure 14-8. The edited text.
You can center the writing in the document: select the text, use the shortcut Shift-Control-A to open the Align and Distribute panel, make the selection Relative to Page, and click the button that has the tooltip “Center on vertical axis”, as shown in Figure 14-9.
Figure 14-9. Aligning objects.
Before using this text for a laser cut, you need to convert it to a vector path, so that the outcome will be accurate on any machine. Be careful, because you can’t undo this operation and you won’t be able to easily edit the text any further. To be sure you have a backup, duplicate the layer that has the text and work on the copy. If you make a mistake, you can always throw it away and make a new copy of the original text layer. When you’re finished, hide the original layer.
With the Shift-Control-L shortcut, open the Layers panel, double click the layer name, and rename it with a more descriptive name than Layer 1, as shown in Figure 14-10.
Figure 14-10. Renaming a layer.
Then, right click on the layer name and select Duplicate Current Layer. Rename this new layer, too. Renaming layers is not mandatory, yet it is strongly recommended because it helps you figure out which object your are working on.
Hide the original text layer by clicking on its eyeball icon. Select the text in the duplicated layer and, from the Path menu tab, select Object to Path. You can double-check the conversion by pressing F2, which allows the direct editing of the various paths. See Figure 14-11.
Figure 14-11. The text, ready for cutting.
Laser printers translate vector line color to laser intensity. A fully black line, for example, indicates a fully powered laser cut. If you merely want the laser to add some shading to your material instead of cutting all the way through, you have to lighten the color of the line. Make sure all the text is still selected, then use the shortcut Shift-Control-F to open the Fill and Stroke panel. From the Fill tab, select a Flat Color RGB with values [128, 128, 128], which represents a medium grey, as shown in Figure 14-12.
Figure 14-12. Changing the text filling.
You have now modified the inner part of the text, but if you don’t want each letter to be cut out, you still have to modify the outlines. Go to the Stroke Paint tab, select Flat Color, and set the strokes to RGB [128, 128, 128]. Then go to the Stroke Style tab and select 0.010 mm for the Width: you can see the result in Figure 14-13.
Figure 14-13. The text, ready to be processed.
Now draw the outline of the sign: click the Rectangle tool, or press F4. (Inkscape has shortcuts for nearly everything, and the more you learn, the more productive you’ll be.) Change the settings so that you have no filling and a full black outline, then draw a rectangle around the writings. You can do this on a different layer if you like, for the sake of simplicity and clearness.
You can modify the corners of the rectangle by dragging the perimeter indicators as you learned from the tutorial (you did go through it it, didn’t you?) or editing the values from the toolbar boxes as shown in Figure 14-14 .
Figure 14-14. The sign outline.
Let’s move on to the images.
You can start with the one on the left (Figure 14-15), which you can find online. Download the image to your computer. From the menu File, select Import and insert the image into the Inkscape document. A dialogue window will pop up, asking whether you want to embed the image in the document, or just link it. Choose embed, the default setting, and confirm. Scale and drag the image to its final position.
Figure 14-15. The sign has now a logo, too.
Once the image has been positioned, you have to turn it into a path, ie. a vector graphic, like you did with the text. Let’s learn a new trick: image tracing. Select the logo and, from the Path menu, select Trace Bitmap. Different images need their own settings; in this case, you are only interested in the outlines, so you can copy the configuration from ones in Figure 14-16. Click OK, then close the Trace Bitmap window.
Figure 14-16. Transforming the image into a path.
But wait! There are now two logos; one in full color, and one in black and white, one directly on top of the other. You have to discard the colored logo, which you no longer need. Drag it away (Figure 14-17) to avoid any mistake and press the Delete or Del button.
Figure 14-17. Discarding the colored part.
If you have the two paths of the outline remaining, rather than just one, select the inner one and discard it.
You now need to follow two separate paths, because each side of the image will have a different filling. Click Path and select Break Apart (Figure 14-18) .
Figure 14-18. The separated paths of our logo.
Now, select each one of the three parts and choose Object→Fill then set the Fill for one shape to [101, 101, 101], the other to [53, 53, 53], and the third to [93, 93, 93]. Done! It wasn’t hard, was it? Figure 14-19 shows the design so far.
Figure 14-19. The logo, ready for cutting?
Now we only need the last image...
We could repeat the last procedure, but let’s try and do it all manually, to get familiar with the tools. For the black you have in the original image, you’ll use a deep raster incision, which could correspond to the black on the vector graphic. Create two rectangles with rounded angles; they will be Frankie’s face. Set the fill to none and the stroke to a 4px or so solid line, as shown in Figure 14-20.
Figure 14-20. The logo, ready for color filling.
Of course, the two rectangles are no good like this: we will only keep the outline. Select them both, then from the Path on the menu, choose Union and obtain a single shape, as shown in Figure 14-21.
Figure 14-21. The face outline.
For the hair you can use the Bézier tool for lines and curves, with the shortcut Shift-F6, then draw the outline without worrying about what happens around the head, as shown in Figure 14-22.
Figure 14-22. Before the hairdresser.
Select head and hair, then from the Path menu, choose Division. Select the hair and change the filling (Figure 14-23), and now you’re a barber!
Figure 14-23. “Figaro qua… Figaro là…”
The eyes are very simple: first draw a circle with black outline and white filling, then position another black circle within it. Copy both circles and resize the outer one. Now to the nostrils, which are two simple white circles, and the scar, made of a horizontal line aligned with a diagonal one, copied several times and regularly distributed. For these steps, use the Align and Distribute panel again.
For the mouth, draw a rectangle with rounded corners, overlap another rectangle to it and, from the Path menu, select Difference, then select the top corners of the mouth, click Break Path at selected nodes and finally delete the horizontal line. Now, your file is ready for cutting! (Figure 14-24.)
Figure 14-24. The model, ready for cutting.
Now that you are an Inkscape master, you can go crazy with your creations. But before you do, read the next section...
Optimizing a File
The cost of a laser-cut artifact depends on many factors, not least of which is the material itself, and the time needed for cutting. To reduce your costs, there are nesting techniques which minimize unused space and optimize the cut. When you work at this kind of thing, you have to be careful and avoid double cutting lines, which originate when two shapes brought together end up with one line in common. This could have a negative effect on the material and also would be a waste of energy, since the cut would be carried out twice. To remove all double lines you can use the same technique you used for the mascot mouth in our example.
We all know that if you’re using a saw to cut wooden boards, you need to adjust the measurements because the saw is going to “eat up,” or “waste” a few millimeters: the same happens with a laser cut, though on a smaller scale. In jargon, the material that gets lost with cutting is called kerf. In laser cutting, the amount of kerf depends, among other things, on the material, its thickness, the kind of laser, the lens and its focus. Roughly, we are talking about kerf of a few tenths of millimeter. Of course, the good old rule of “measure twice, cut once” is also valid for laser cutting. You have to take that into account when you design our project, especially if you have joints, which need to be as precise as possible.
The laser slows down along curves, so straight lines are faster. Also, it is worth placing the longest straight lines parallel to one of the laser cutter’s axes, so that during cutting only one motor will move.
For laser cutting, as with almost any other maker’s activity, an iterative approach is crucial: before cutting the material you want, it always better to make a cardboard or paper prototype, even in smaller scale, to fix possible mistakes and spend a fraction of the cost to make the finished product. It sounds like a waste, but you won’t regret it.
Tricks for 3D
As we said earlier, you can make 3D objects with a laser cutter by combining flat, laser cut shapes. In order to manage joints in the best possible way, there are some tricks you can use. They help you consider kerf, unevenness of the material, and so on.
Moreover, each material has its own peculiarity; when you design joints for plastic objects, for instance, it is a good idea to include a small circle at the corners, called relief groove, to better release forces and avoid any breakage of the material. Figure 14-25 shows a diagram from one of Ponoko’s laser cutting tutorials. Ponoko offers laser cutting among many other services.
Figure 14-25. Careful with those corners! (Ponoko).
There are many other examples to be found on the Internet and even more sources of inspiration. Now you have everything you need to create wonderful objects... you only need to learn how to make them come together!