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Lasering Wine Glasses

Copyright © 2011 by Davis Multimedia, Int'l. All Rights Reserved.
As Printed in December 2011, Volume 37, No. 6 of The Engravers Journal
Using a Plexiglas fixture and my old New Hermes GTX vise, I was able to tilt the glass so the engraving area was horizontal.

   Grapes are not the only things that come in bunches. During one week last fall, two different customers brought in wine glasses for engraving. The first was a local (Tampa) high school alumni class celebrating their ten-year reunion who brought in 61 for me to engrave. The second order was even larger. A marketing company that was helping to promote a condominium complex in Sarasota needed 106 wine glasses engraved.
   Generally speaking, laser engraving wine glasses shouldn’t be too much of a problem but, then again, we always run into those jobs that involve a bit more than meets the eye. On the surface, it would seem that these two jobs were very similar. In reality, though, they each had their unique complexities and those were compounded by the fact that I don’t have a cylindrical fixture for my laser engraving machine.
   Of course, there is no flat spot anywhere on a wine glass; it is just a whole series of big compound curves. Wine glasses have a bulge in the middle, a smaller top and a rapidly changing curvature where the bottom of the bowl meets the stem. In order to successfully engrave a wine glass, you need to identify the flattest area on the glass and then place it in the machine in a manner so that the chosen area can be reached by the laser.
   We know that the laser beam must be in focus in order to mark the material to be engraved. We also know that a small deviation in focus will result in an acceptable mark, but a large deviation will not make an acceptable mark or perhaps not any mark at all. A slightly out-of-focus beam will sometimes make a satisfactory mark if the power is turned up higher than what would normally be used for a focused beam. However, when this slightly out-of-focus method is used, some resolution will be lost because the spot diameter of the out-of-focus beam will be a bit larger than a focused beam.
    There are cylindrical attachments available for laser machines that are designed to engrave around the circumference of round items. Some of them feature multiple adjustments that allow you to “wiggle” the pseudo-flat area under the beam. But, as I mentioned, here at G.L.G. ART Custom Engraving, we don’t have a cylindrical fixture. If you don’t have one either, it doesn’t mean you have to turn down roundwork jobs. Instead, you just have to turn up the brain by putting on the thinking cap and making some fixtures to accommodate the challenges that wine glasses can present.
   A look at geometry will provide some information about the amount of curve that you can get away with using the “approximate” flat area method (Fig. 1). For a 3" diameter glass, a horizontal distance of 1" will have a drop off of 0.080" as the beam travels away from the exact center of the diameter. After that, the drop off accelerates greatly. If the item you’re engraving is raised upwards by 0.04" (one half of the drop off due to the curvature), then some of the engraving is slightly closer to the lens, some is slightly farther from the lens and some is exactly in focus. This compromise can often produce an acceptable engraving result. Fortunately, glass is one of the more forgiving substrates when you use this method. Figure 2 shows the formula I used to determine the approximate flat area on curved items with various diameters based on a .080" drop off.
   With this in mind, we studied the glasses brought in and the messages that the customers wanted engraved on them. The marketing customer had a logo that measured 1.6" wide that they wanted engraved on 22 oz. red wine glasses. There was no way that this logo could be engraved in one pass because of the curvature on the glass. I needed to devise a fixture and method that would allow me to engrave the logo with the best quality results.


Figure 1: The geometry of laser engraving a wine glass. Figure 2: The formula used to determine the approximate flat area on curved items of various diameters based on a .080" drop off.

    I decided to use my old New Hermes GTX (pantograph) cup holding fixture that came with my manual engraving machine many years ago. After measuring the glass, I determined that the slope of the sides was 15 degrees. Next, I made a Plexiglas fixture to hold the fixture and that allowed me to tilt it to accurately reposition the circumference of the glass under the laser beam. I clamped the 22 oz. wine glass in the vise using the cones that were part of that system. By tilting the vise in the laser, I was able to position the glass so that its tapered section was almost perfectly horizontal under the laser beam (see opening photo). Using math and some trial and error test engraving, I also determined that each turn of the hand crank rotated the glass 3.60 degrees; therefore, exactly 5 turns of the hand crank would equal 0.60" on the circumference of that glass.
    Next, I created a 0.60"x1.00" layout that represented the flat area to be engraved on the glass. Using CorelDRAW’s convert to curve and breakapart commands, I broke the logo into three segments and positioned it in the layout (Fig. 3). To test the positioning, I covered the glass with Laser’s Edge tape and then engraved the first third of the logo at a low enough power setting so the image would show up on the tape but not cut through it and onto the glass. For our 50 watt Universal Laser machine we used 10% power and 100% speed for this operation. If you are not sure what settings you should use on your particular machine, you will need to do your test cuts on some scrap material instead of the customer’s actual product.
    After making some adjustments as small as .001", I was confident that the setup was satisfactory. I removed the test tape and changed the power setting to 100% power while leaving the speed at 100%. The first glass was ready to engrave.

Figure 3: The CorelDRAW setup used to engrave the logo. Figure 4: The finished product.

    The 22 oz. wine glasses were fine crystal, so they were quite thin and delicate. Every time I tightened the vise to clamp a glass, I was nervous about possibly over tightening the vise and breaking it. In our shop, we have two levels of “tight”: monkey tight and gorilla tight which I believe are pretty well self-explanatory. For these delicate wine glasses, I used “monkey tight” to provide a snug grip, but not overly snug. If you look closely at the photo at the beginning of this article, you can see that I also used two pieces of masking tape at the base of the glass as extra insurance against the glass slipping off the holding cone.
    With the glass held securely in the vise, I engraved the first third of the logo, then cranked the handle exactly five turns and engraved the second third of the logo, cranked the handle another five turns and finished the logo. To achieve proper alignment of the three images, you must remember to crank the handle and advance the engraving job in the software and keep track of what you are doing. Any distraction could cause a misstep and bad results. Figure 4 shows the finished product.
    The Wharton High School glass was a bit different. Their predominant school color is blue and, as a result, the woman heading up this project chose blue wine glasses. We discussed the information to be engraved on the commemorative keepsakes. She settled on “W.H.S., Class of 2000, 10 year Reunion.” Graphically we stacked this information in a vertical manner which meant the maximum engraving width for the layout would be 1.12". This is on the very edge of engraving without having to rotate the glass for a second pass.

Figure 5: The Plexiglas fixture used to hold the blue glass.

Figure 6: The blue glass and fixture in the upper left corner of the laser table.

Figure 7: The finished product.

   I made a fixture to hold this particular glass once again by cutting Plexiglas with the laser to form the parts and solvent welding them together. I included curved cutouts to support the bowl and stem, and a flat plate to provide a firm stop for the top of the glass to rest against. Next I tilted the entire fixture upward at an angle of 10 degrees to accommodate the slope of the sides of the bowl (Fig. 5).
   Because the engraving could be completed in one pass, this job was easier to accomplish than the previous job. Figure 6 shows the glass placed in the upper left corner of the laser machine and Figure 7 shows the finished engraving with the glass still in the fixture.
   A little side note: The glasses for both of these jobs had to be removed from a lot of protective packaging, engraved and then returned to that same wrapping. It takes almost as long to unwrap and wrap the glasses as it does to actually engrave them! To avoid wasting time, I unwrapped one glass and repackaged another while one was being laser engraved.
   Speaking of wrapping, I’ll wrap this up by encouraging you to challenge and stretch yourself with interesting work. If you get the chance to engrave wine glasses, say yes. Don’t turn them into “whine glasses.” Oftentimes the mundane pays the bills and provides a string of low stress days. But as one of my EMT friends once told me, “Stimulation promotes growth” so, every now and then, go out on that limb by taking on one of those adrenalin-pumping, challenging jobs. It is fun and it can be profitable if you’re careful. Just try really hard not to saw it off behind you.

 

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