For Christmas presents this year, a couple family members wanted stemless wine glasses. Instead of going with the standard Crate & Barrel glasses (which I wound up using to etch), I decided to etch custom wine glasses with a monogram on one side and a grape vine design on the other. This wound up coming out at least as well as I had hoped, thanks to the high resolution helix laser and relatively flat sides of the Crate & Barrel glasses. I made this at the San Jose TechShop - www.techshop.ws.
Step 1: Drawing the Design - or Finding One
I used a grape-vine design on one side of the glass, but you could use any design you wanted - as I learned halfway through this project, you don't need a vector file to etch glass, you only need it for cutting, which you can't do to glass with a laser anyways.
The first step to creating your design is finding the pattern or image, or creating one yourself. When I was looking, a quick Google images search for vector-based grape vine graphics turned up some pretty good designs, but none that I liked as-is, so I wound up heavily editing one of the existing designs to get my pattern. While you don't need the vector graphic, it does make scaling work pretty well. After you pick out the image you are going to use, make sure you make it "laser-friendly." To do this, convert the image to black/white, not just grayscale. If you haven't done this before, in Adobe Illustrator, you can change the color scheme to grayscale, and then select the whole background region using the select by color tool, and clicking "Inverse Selection" under the "Selection" menu. This will select everything to be etched, which you will then want to paint black. Make sure you realize that the color will actually be reversed - etched glass is white, and red wines/dark beers/most other drinks are not, so etching something that is normally black and white will require you to switch your colors if you want it to look right.
On the rotary attachment on the laser, the laser will spin the piece as it goes, but it will treat the piece as if it is flat and starting from the top left, from the perspective of the image design. Therefore, the top of your glass is on the left side of the layout, and the top of your layout is the starting point of where the laser will start rotating around the glass. On the Crate & Barrel stemless wine glasses, the circumference is 8.64", and therefore the height of your design is 8.64 inches. If you are using a different glass, remember that you will need to measure the distance across the top of the glass, not the average, as the rotary attachment spins the top of the glass. Also, keep this in mind when designing your graphic - on a beer glass, you may want to stretch out the right side of each object (which will actually be the bottom) slightly to account for it being compressed on the glass.
One final note on graphic design for the rotary attachment, regardless of what you are trying to etch: if there's a taper, do not put a line around the glass, or anything else that must line up. Text wrapping all the way around is also a bad idea, if in the same font/on the same level. Due to a combination of possible dust on the drive wheels of the rotary attachment, uneven friction from the rear support wheels, imperfections in the glass, and a good old dose of Murphy's law, you will never get a line to actually line up. On my original design, I used a 7px line on the top and bottom of the glass, and it looked terrible. With the design I settled on (the same, but without the line) it was probably still off, but you can't tell. 1/16" is only obvious when your design points it out, but when it does...
Step 2: Etching the Glass
To actually etch the glass, you will need to use the rotary attachment in a helix laser cutter/etcher. If you don't know how to install the rotary tool, please have someone who does teach you how, as it is easy to break the machine by installing it incorrectly.
To etch the glass, place it with the open end towards the left side of the laser (with the drive wheels) on the rotary attachment. Remember before you do this that when you press the focus button with the rotary attachment installed, the laser will move the lens to the left side of where it thinks the work piece should start, and if the table is too high, will break the work piece and/or lens. Bring the glass into focus at roughly the center of the glass, and disable X-Y in order to manually check to make sure that the laser will not hit the work piece. If it will, you may need to move the table down, place washers under the left side of the rotary tool so as to lift it slightly, and then re-focus the piece. Using the height adjustment on the right side of the rotary attachment (the bottom of the glass), make sure the top of the glass is as close to level as possible. You will not be able to fully level a wine glass due to it's shape - that's fine, just get it as close as possible, and focus close to the average height, again ensuring that the laser's mirror will not hit the work piece.
When the piece is set up and the laser is focused, you are ready to print the design. Under the printer settings, make sure that Vector cutting is disabled, only using Raster. I used 600dpi, 90% power on a 60 watt laser, and 45% raster speed - the recommended 55% does not work on a wine glass, as it is not focused well enough. After you etch the piece, clean off the piece with a soft cloth to remove the micro shards of glass that will now be covering it. DO NOT wipe it off with your hand, or your hand will itch for the next week - this is a mistake you only make once. Your work piece is now complete, and as dishwasher safe as it was before - unlike the printed glasses, etched glasses to not wear out over time.