Laser Cutting Acrylic for a Flame Polished Edge: Part 3
The focal lens choice will play a role in the edge quality. Ideally a 2.5” lens will work with thicknesses up to 3/8-1/2”. Anything thicker may require a 4”, 5”, or maybe even a 7” lens. This is where laser power will come into play. When the focal distance increases, the amount of energy of the laser will seem to decrease. Not having enough power will mean slowing the laser down significantly to cut through the material. There is a point where cutting slower will not work because it will increase the chance of flare-ups that can occur when cutting acrylic too slow. Acrylic is flammable and the only cure for this is more laser power. Then the acrylic can be cut at optimal and production friendly speeds and still get the nice polished edge. Achieving a high quality edge with multiple passes is very difficult.
Focal point will have an effect on the angle of the cutting edge. The thicker the material the deeper “into the material” the focal point should be. For acrylic over 1/4" thick, you should focus in 1/3 of the total distance ( ½” acrylic would need to be focused in approximately 3/16”.) This will keep the edge as straight as possible. The longer the focal point of the lens, the straighter the edge will be.