Precision with a Laser

 

The laser cutting blade.
The infrared energy of the CO² laser works just like a saw blade without all the dust and noise. A computer controller built into the laser system translates the graphic design into X and Y coordinates in the same way a plotter works. The controller translates the graphic design into two modes of operation called raster or vector. Raster mode is for engraving and the motion system will move right and left at high speed. Vector mode is when the motion system moves in a free form manor following the outlines of the design software. When vectoring using a high power setting the effect can be cut all the way through a material or a lower power setting can be used for vector engraving fine lines.

The key to determining whether graphic is raster or vector is to adjust the outline thickness of the graphic. A line with thickness of .003 in. or less will be seen by the laser as a vector graphic. A line with a thickness of .004 in. or more will be seen by the laser as a raster graphic. As a general rule the dimension of .003 in. works with most software and laser systems, but not all. Be sure to consult your operators manual or system manufacturer for the exact vectoring specification for your system and software combination. To be absolutely sure a graphic will vector I have adjusted all the defaults in my Corel DRAW v8.0 to a setting of .00005 which is the minimum the software allows.

Another feature in the dynamic of laser cutting is understanding how your laser pulsed during operation and how this can effect the cut quality. The higher the frequency of these laser pulses, the greater the overlap of the pulses which result in a smoother cut. The laser pulse frequency is easily controlled in your print driver using the PPI (Pulses Per Inch) or Rate features. As a rule, the higher the Rate or PPI setting the better quality of cutting.

Also requiring consideration is the spot size of the focused laser beam. Laser focus lenses are given a focal length which translates to the distance from the bottom of the lens to the table. Most laser systems come standard with a 2.0 inch focal length lens. A 2.0 inch lens creates an average spot size of .005 inch. The focus lens creates a cone shaped beam starting at the lens and down to the small spot it creates. The angled sides of the cone can create a slightly beveled edge on some materials that are cut. This effect of the focused beam can sometimes be compensated for by using a shorter focal length lens, increasing the power, using a mid-point of focus on the material or a combination of these depending on the material and laser power.

Real cutting applications.
After understanding a few of the basics, the best thing is just to set aside some time and just start experimenting with a few projects to get going. Some of the many applications for cutting wood sheets include making drink coasters, window and holiday ornaments, appliqués for plaques, dimensional lettering, name badges, stand up displays, engraving fixtures and so much more.

Starting with a basic project like a drink coaster is simple and illustrates the process. Since we are working with wood sheet material that is 4 inches wide, pull down a guideline from the top ruler to illustrate the dimensional size of the wood sheet. Next draw a circle that is just slightly less than 4 inches in diameter and center it vertically. (Hint: holding the Control key down while drawing the circle will create a symmetrical shape) Since we will be vector cutting this circle make sure the thickness of the line is .003 inch or less. The line thickness can be changed using the Pen Dialog feature.

Now add some text or graphics inside the circle to complete the design. As an example, we can add text or corporate logo that will be raster engraved into the wood. The text is simply typed in and scaled to fit and the logo is imported from a logos package. After aligning all of the graphic elements the completed design can be pasted to fill the whole sheet of wood by first grouping all of the objects together and then using the duplicate feature.

The completed graphic is then printed to the laser for the engraving and cutting operation. For a 30-watt laser system engraving settings of 100% speed and 75 % power and 600 dpi were used for engraving with cutting settings of 10% speed and 35% power and a RATE setting of 100 for cutting the 1/8 inch Alder sheet wood.

Layering vector art.
The same concept can be pushed a little farther by working on a design that uses two different power settings for vectoring, one a light cut and another at a higher power for through cutting as we did above.

The holiday ornament graphic was pulled from the symbols collection of Corel DRAW. The line thickness was changed to the correct dimension for vector cutting with the addition of a different color of line for the cutting of a foil. We chose the color blue for the low power cutting areas and the color red for the high power cutting vector lines. The blue lines will be cut first so we need to select them and use the Order tool to send them to the back layer. (Hint: select the object then use Shift + Page Down keys) The laser system will see blue graphics on the back layer first and run them before cutting the red vector lines.

Now that the graphic is prepared, print it to the laser in the normal way and be sure to select the color-mapping mode if needed. Each color (red and blue) can have separate power and speed settings. Use the same power and speed for cutting all the way through as we found in the above exercise and apply it to the red color. Use the same speed setting for the blue color and lower the power setting to just 10% of the power needed to cut all the way through the wood.

The final step is to prepare the wood sheet by applying the foil to the top surface. The laser foil comes in a variety of colors and applies like a tape to the wood. Since we will also be cutting all the way through the wood for this project it would be wise to protect the foil from the hot smoke residue created from the high power cutting action. After applying the foil to the wood use a top layer of medium tack paper mask. The paper mask works great to protect the clear coat on the wood surface and the foil material from being damaged during the laser cutting procedure.

After laser cutting the wood sheet with the ornament design remove the paper mask and unwanted areas of foil. Any left over wood residue can be quickly removed by using a soft cloth dampened with water. The finish product sparkles from the precision cut foil and the dimensional look of laser cut wood.

Cutting stand up displays.
Creating a 3-dimensional project from flat wood sheets is far simpler than it really looks. The secret to this process is to make a small tab on the vertical part of the display that will interlock with a corresponding slot cut out of the base part. Creating this interlocking tab requires quick review of the laser theory section referring to the laser beam spot size. As the focused beam cuts through the wood sheet it creates a kerf or gap from the wood that was vaporized. In theory the material removed by laser cutting is the size of the actual focused laser spot size. In reality the intense and focused laser energy actually removes more than the size of the laser spot as the wood continued to burn a few milliseconds after the beam had passed by. Compensating for the 'growing' of the kerf is a little bit of an educated guess because each wood piece reacts slightly different to the effects of the laser energy.
Start the design of a stand up display by drawing a 6-inch wide by 3-inch tall rectangle. To create a more finished look to the display round the corners slightly by adjusting the Rectangle Corner Roundness tool to a setting of 10. Create another rectangle that is 2 inches wide and .125 inch tall. (Hint: 1/8 inch sheet wood is .125 in decimal form) Center the smaller rectangle along the lower edge of the larger rectangle so the two objects barely touch. Be sure to select both rectangles then click on the Weld tool and weld the two rectangles together. You will see the top edge of the smaller rectangle disappear and the all-important interlocking tab created.

Now create the base by drawing a 4-inch wide by 3-inch tall rectangle with the same rounded corners. Draw a second rectangle with the dimension of 1.99 inches and .124 inch that will become the slot for the tab to slide into. Note that these dimensions are slightly smaller to compensate for the material removed during the laser cutting process. Align the smaller rectangle into the center of the larger base rectangle. Add the text and graphics to be engraved and the layout for this project is complete.

The resulting interlocking joint should be firm but not so tight to crack the wood. Small adjustments may need to be made to the vector artwork to compensate for variations in the wood. Slightly wetting the wood with water helps to make the pieces fit together creating a strong, glue less connection.

Laser manufacturing.
With the ability to engrave and cut the compact laser system can truly be called a Laser Manufacturing Center. Sheets of materials like plastic, wood and acrylic can be personalized and cut with precision tolerances to make valuable products from affordable raw materials. If you have a laser system, take the time to learn how to manufacture volumes of products by attending a workshop to learn how to make the most of your investment. If you have been considering the purchase of a laser system, now is a good time to take advantage of this reliable technology with virtually unlimited capabilities.