This tutorial shows how to make a DNA double helix necklace on a Trotec laser engraver. I made it at TechShop.

For the most part, the actual cutting process on the laser cutter is pretty straightforward. The toughest part is creating the computer file that tells the laser cutter where to cut. As a result, this tutorial is primarily focused on how to use adobe illustrator to create cut paths, not how to operate the laser cutter itself.

I'll do my best to make this accessible for new Illustrator users but some tools are a little tricky to figure out (and describe) how to use; you just need to play around with them a little to figure out how they work. It can be a little frustrating at first but you'll quickly pick it up.

Supplies you'll need:

1. A TechShop membership. (Or access to a lasercutter)

2. Material to cut the pendant from. I made some from high density fiberboard and some from acrylic.

3. String or chain to make the necklace.

Step 1: Drawing the Double Helix in Adobe Illustrator (Step 1)

Create a new file, it will bring up a window with the document settings. Set the profile to basic RGB and adjust the dimensions to fit your project. If the image is not in RGB mode the laser cutter will not be able to read the cut lines.

First, use the pen tool to draw the shape in the first picture. First click where you want the bottom corner to be, then click (and do not release) where you want the top corner to be then drag the cursor up to create a bezier curve handle. At the upper point there will be two handles created, one above and one below the end anchor point. Use the one below to make the end of the line exactly vertical (when the handle is vertical, the curve will be vertical at that point). You can hold down the shift key while dragging the handle to constrain it to 45° increments.

Next, use the rotate tool to rotate the shape you just created 180°. To do this, select the line you just made, double click the rotate tool on the toolbar on the left, change the angle measurement to 180 and click the copy button. Next, drag the copy so that the top left anchor point of the copy snaps on top of the bottom right anchor point of the original, see the second photo for an example. Next, select both line segments at once and join the two paths into one using Ctrl-J (or Cmd-J on a mac).

(Note: it is not strictly necessary to join all the paths, but if they are joined then the laser cutter will cut them in one continuous motion instead of cutting a bunch of individual segments, often out of order.)

Next, use the reflect tool to produce a mirror image copy of the path you've created. To do this, first change the rotate tool into the reflect tool by clicking and holding until the tool choice menu pops up and select the reflect tool. Next, select the line and double click the reflect tool. Reflect it either vertically or horizontally (it doesn't matter because it has rotational symmetry). Be sure to click the copy button this time as well. Now, drag the copy so that the top right anchor point snaps in place on top of the bottom right corner of the original. Again, join these paths. See the third photo for an example.

Finally, make a copy of the shape you've just created. The simplest way is to select the line. Then hold down the Alt key and drag the selection with your cursor. This will create a copy but leave the original path where it was. Again, line up upper left anchor point of the copy with the bottom left anchor point of the original and join the paths. See the forth photo for an example.

Step 2: Drawing the Double Helix in Adobe Illustrator (Step 2)

Next we need to make a copy of the curve we drew in step 1. The simplest way to duplicate it (that I know of) is to select the whole curve then hold down Alt and drag the curve down with the cursor (do not release the Alt key until you have released your mouse button). You want it lined up vertically with the other shape, illustrator will help you keep the center lines lined up, but if that's not working for you, you can use the align tools on the upper tool bar. See the first photo.

There is an anchor point at the vertex of each peak and valley; you want to connect them with a straight line. Simply use the line tool, illustrator will help you snap the cursor to each anchor point. See the second photo.

Next, make a reflected copy of the entire shape and line up the center lines. It is up to you if you want them lined up vertically. Some drawings of DNA have it displayed that way, but in reality DNA has a major groove and minor groove. This is why my reflected copy is offset below the original. See the third photo.

Step 3: Drawing the Double Helix in Adobe Illustrator (Step 3)

I needed to do something to close up the ends; this step describes the strategy I used.

First, I grouped all the parts drawn so far. To group a bunch of objects, select them then press Ctrl-G. Next I drew an ellipse (using the ellipse tool). I centered the ellipse and double helix as in the first photograph.

Next, I used the cut tool (hotkey: C) to cut the paths of the helix and the ellipse where they overlapped.

Then I used the direct selection tool (hotkey: A) to select the ends of the helix that extend beyond the helix as well as the arcs of the ellipse that were not closing the ends of the helix ribbons. Next I used the delete key to delete them. See image #2.

Step 4: Drawing the Double Helix in Adobe Illustrator (Step 4)

Next I added the rungs. To do this I first drew a rounded rectangle with an appropriate length and width and made 12 additional copies (again using the Alt-drag method). Then I visually aligned the top and bottom rungs with the top and bottom places where the ribbons cross and used the align tool to distribute them evenly in between. See image #1.

Next I used the arrow keys to align each rung individually so that it fit between the ribbons (using the left and right arrows only kept the rungs equally spaced). I had to adjust the width manually as well.

Next I wanted to cut all the lines wherever there was a cross. The simplest way I found to do this was using the trace button on the pathfinder tool. Press Ctrl-A to select all the lines, press the trace button in the pathfinder window. When you do this, all your lines will disappear and will be replaced with lines that contain no stroke and no fill. You will need to add back the stroke width and color.

The laser cutter at TechShop requires that cut lines have a stroke width of 0.01 pt and pure red (RGB = (255, 0,0)). Because I needed to choose a stroke width and color for the trace lines I elected to set them to match the laser cutter requirements at this point. If you are following along, you will notice that at this point if you use the direct selection tool that each segment terminates wherever there is an intersection. See image #2.

Next, I deleted any segment that would have been behind the ribbon. See image #3.

Step 5: Drawing the Double Helix in Adobe Illustrator (Step 5)

The next step is to change some of the cut lines into etch lines. You wouldn't want the laser cutter to cut everywhere there is a red line because the whole thing would fall apart. Instead, you only want to cut the lines that define the outline and etch the lines that separate the ribbon from the rungs. As noted earlier, illustrator reads thin red lines as cut lines; it reads black lines as etch lines.

I found the best way for me to keep track of which lines need to be cut and which need to be etched was to create a second layer and turn off its visibility. This way, you can select the segments you want to etch, switch to the invisible layer, then using the menu bar at the top select Object -> Arrange -> Send to current layer. This will make the segments you don't wish to cut disappear. Do this so that only the outline remains. See image #1.

Next, make the invisible layer visible and the currently visible layer invisible. Now select all the segments that you moved to the new layer and change their color to black and their stroke width to something thicker (I used a 2 pt stroke width). See image #2.

Step 6: Drawing the Double Helix in Adobe Illustrator (Step 6)

I wanted to have a double helix that had a stylized curve instead of having parallel rungs. To do this, I turned it into a brush.

Turn back on all the layers visibility. Select the entire drawing so far. Click the brushes button on the right side menu. It will open the window shown in image #1. Click and drag the image you've drawn so far into the brushes window. This turns the drawing into a brush.

Now delete the drawing from your canvas because you will be using the brush you've just created to make a new curved version.

Use the pen tool to create a curved line on your canvas. Click the new brush you made in the brushes window and the line will be replaced with a double helix that follows the shape of the curve. See image #2.

The last step (which I forgot to take a screen capture of) is to draw two small circles (cutlines) on the ribbon at the top for the necklace chain or string to go through.

Step 7: Cutting the Pendants on the Laser Cutter

If you are a TechShop member with access to the laser cutters you already know how to operate them.

In order to minimize the scorching that can occur when cutting and engraving I like to cover my pieces with painters tape before running them through the laser cutter. See image #1.

Open the illustrator file and print the image to Trotec JobControl. Focus the laser and engrave away. See image #2.

Peel away the tape and reveal your newly completed DNA pendant. See image #3.

Attach it to a chain or string and your necklace is complete. See image #4.

Good luck and happy TechShopping!