Awards & Engraving

August '18

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16 • A&E AUGUST 2018 The task is to find the length "c," the diameter, technically a chord, where the ornament rests on the turning wheels. Everything else is a known value. r = radius or 1/2 diameter c = chord or 2*(SQRT((r*r)-(x*x))) x = distance of chord from centerline or half of the wheel gap Ornament diameter =2r Wheel gap = 2x Percentage adjustment = (c/2r)*100 For Formula Buffs Only much laser power to vaporize it and expose the silvering. Power should be set relatively low. Heat can also be reduced by changing the color-fill from pure black to a shade of gray. This reduces the chance of cracking by keeping the laser pulses from overlap- ping too much. The engraving drifts and looks crooked. Even weighted down with sand or rice, the ornament can turn unevenly on the rotary. Glass ball ornaments are hand-blown and are sometimes slightly out-of-round, particularly away from the equator. If an out-of-round section rests on the turning wheels of the rotary device, the ornament can turn unevenly as it is being rastered. The result is usually not apparent with small graphics but is noticeable with long strings of text. This is where a spe- cialized jig is appropriate. There are many different styles of jigs, but the goal is the same: to keep the band around the equator rotating straight relative to the laser. The engraving looks like a negative. Exposing silver against a dark background is like writing with chalk on a blackboard. To get a positive graphic image, the graphic must be inverted (made into a negative) in the drawing. Text is usually an exception to this rule. The engraving is distorted; circles and squares are stretched. When marking or engraving insulated tumblers and glass- ware, if there is a taper, the graphics in the drawing need to be adjusted to avoid looking compressed or elongated when engraved. The same goes for a sphere, which has a continuous taper in all directions. Why does this happen? When the work piece on the rotary device has a circumfer- ence on the turning wheels that differs from the circumference where the graphic will be engraved, the area where the graphic goes travels a different distance over a given time (thus at a different speed) than the part on the turning wheels. If the circum- ference is larger where the graphic goes, the engraved graphic appears stretched; if smaller, it appears compressed. This can be accommodated for in the drawing by either compressing or stretching the vertical aspect only of the drawing. To do this, divide the circumference at the turning wheels by the circumference where the graphic goes and multiply that by the vertical aspect only of the drawing before sending it to the laser. (I use circumference because it's easy to measure on most items with a cloth tape. Diameter will also work in the same formula.) Another method to determine the adjustment factor is to use a formula based on the separation of the turning wheels and Laser Engraving

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