There are a lot of instructables showing the steps to etch anodized aluminum using raster graphics, but this one will be specifically using vector graphics. When etching with a vector graphic, the laser moves along the graphic's lines, instead of back and forth along the width of the image etching dot by dot. This can produce higher quality etching faster for some applications.
Here, I etched the seatpost on my bike to add measurement lines. The seatpost is black anodized aluminum. It is very important that this is not done on polished aluminum because any reflected laser can hurt the laser cutter.
The laser setup:
First I removed the seat and mounting hardware. I used the rotary attachment in the laser to etch on the curved seatpost. You can see the setup in the second picture. I used the spring loaded support wheel, but I removed the wheel part because the seatpost did not fit under the large wheel. Maybe if you found a different smaller wheel to replace it with it you could fix the small misalignment that I ended up to.
The vector setup:
I used corel draw for the numbers and lines. My seatpost has its size stamped on it, otherwise you'll have to measure it with calipers. Make the height of your image the circumference (3.14 x diameter) and the length the length that you want to etch. For the lines, I drew rectangles 0.6pt wide. This results in 2 vector lines next to each other and looks well defined. Make sure all graphics are hairline thickness, or else they will be considered raster graphics.
The printer setup:
The fourth picture shows the print dialog with the settings that I used. Make sure to test out the print in an inconspicuous area to find out what speed and power settings will work well to etch the aluminum, without going all the way through and damaging the laser. Remember to modify speed and power to get the desired etch, speed can have a wider effect than power on etching power.
This print took 7:33 and etched the lines first on the way out, and then the numbers on the way back to home.
I ended up with a small offset where the seatpost spun in the fixture. This might be mitigated by installing a small rubber wheel in the spring loaded support, so that the seatpost does not lose traction.