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Track your laser engraver's cutting power with test strips

Picture of Track your laser engraver's cutting power with test strips
Does your laser cut as well as it used to?  Is it time to clean the lenses, perform an alignment, or check the level of the bed?  Is the tube itself losing power?

If you don't have a laser power meter (they seem to start at around $800 for the Synrad Power Wizard), a simple way of making a relative measure of your laser's cutting effectiveness is with a test strip.  This won't tell you what the absolute power output is, but it does provide you with a permanent graphic image of how well the laser is cutting.  In this Instructable, I'll outline how to create an acrylic test strip file and use it with the advanced settings for the Epilog print driver.  The resulting strip will show you how deeply the laser cuts at a variety of speeds (see photo), and is easily compared with other strips.  If you have another brand, you should be able to use the same idea, making changes for your particular laser print driver.

 
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Step 1: Create the test strip

Picture of Create the test strip
If you have a 50W Epilog laser, just use the attached PDF file.

Otherwise, modify (e.g., the Inkscape SVG file attached) or create the artwork using a vector graphics program such as Inkscape (free and open-source), Corel Draw, Illustrator, or similar.  The goal is produce a strip with a number of short vector cuts near one edge, each cut created using a different and specific RGB color that can be mapped to a different laser cutting speed.

(If your laser driver uses a different method of specifying different power/speed settings—for example, line width—you'll need to substitute that parameter in place of line color in what follows.)

Specifying colors

When using the color mapping in the Epilog print driver, it is important to match the colors in your file exactly.  Just picking a random “red” may not work.  Inkscape makes it pretty easy to set and examine the colors in RGB format, which is also the format the Epilog driver uses for colors.  (Setting colors in another color “space” can make it difficult—if not nearly impossible--to match in the Epilog driver.)  RGB format lists the Red, Green, and Blue components of the color using one of two formats--"hex" (hexadecimal, or base-16) and decimal (the common way of writing numbers).  Changing between the hex and decimal values for the purpose of this project is simple--you just need to know 3 mappings:  (full) 255 decimal = ff hex, (half) 128 decimal=80 hex, and (off) 0 decimal = 00 hex.  Any RGB color is represented by 3 numbers in order.  Red, for example, is 255,0,0 in decimal, or ff0000 in hex.  Just to confuse things, Inkscape also shows colors as RGBA--the last 2 digits are the opacity, and usually ff for 100%.  So red would be ff0000ff in RGBA.

1.  Create a rectangular box for the outside of the strip.  3/4" high by a bit under 2" wide should give you plenty of room, and let you cut plenty of test strips out of scrap acrylic.  The line for this box should be thin--say 0.002" wide--in order to be recognized by the Epilog print driver as a vector to be cut.  Give it a “simple” color--for example, in the attached file I used Inkscape's fuchsia (color ff00ff).  (“Simple” in the sense that each RGB level is full on (ff), half on (80), or off (00)--for example, ff0000, 800000, or 000000.)

2.  Add short vectors (say 1/8" long) about 1/16" (or 0.050”) from the edge of the rectangle.  Make each vector a different simple color.  Each will be cut at a different speed.  Here are colors I used along with Inkscape's name for each:

Speed / Color Name / Color number
8 / Red / ff0000
16 / Blue / 0000ff
20 / Lime / 00ff00
24 / Yellow / ffff00
28 / #800000 / 800000
50 / Olive / 808000
75 / Teal / 008080
100 / Aqua / 00ffff

3.  Add a text label above each vector with the speed you'll use.  For 1/4” acrylic on a 50W laser, the speeds above give a range of cutting depths, including cutting through. 

4.  Add any other text explaining what the test strip represents.  Use rectangular blocks to provide a space for writing dates, machine number (if you have more than one machine), and any other information that changes frequently.  But you'll probably want to note the power and PWM frequency as regular text, since the whole point is that you're only varying the speed.

Step 2: Setting the Color Mapping

Picture of Setting the Color Mapping
generalPrintDialog.jpg
In the basic Epilog print driver settings, there are only two sets of parameters used:  raster and vector.  For the test strip we want a different vector setting for each color, and will use the Color Mapping feature.

1.  Attached is a LaserTest.dat file with all of the settings needed for a 50W Epilog Helix.  Save it on your system.  On my computer, the settings are located by default in ...\My Documents\epilog\engraving_setting, but you can browse to any directory you like to load (or save) setting files.  (You can also create the settings file from scratch by matching the settings shown in the photos.)

2.  Load the artwork file you created in the previous step into whatever program you'll be printing from (e.g., Adobe Reader, Corel Draw, etc.).

3.  “Print” to bring up the standard print dialog.

4.  Select the laser printer and then “Properties” to open the Epilog print driver.

5.  Under the “Advanced” tab, “Browse” to the folder with the settings file in it, then load the settings file.  (Verify the size of the work piece under the “General” tab is accurate.)

6.  If you need to change any speeds, under the “Color Mapping” tab you'll see the list of colors and settings.  Click on the color you want to change.  The parameter section on the left will allow you to make any changes (e.g., Speed).  Once done with the changes, click on the >>> icon to update the settings.  Note that the last color, fuchsia, is used for cutting out the test strip (it is the last color to be cut), and is set to 4--a much slower speed than the usual 8 or so for cutting 1/4” acrylic.  This is to make sure the final cut will separate the test strip even if the laser power is decreased.  If you make any changes, be sure to save the settings file (use the Save button under the “Advanced” tab).

7.  If you are creating the settings from scratch, set up the parameters under the “General” tab to match the photo.

8.  Click "OK" at the bottom to return to the generic Windows print window.

Step 3: Run the job

Picture of Run the job
testStripExample.jpg
Using the same thickness of acrylic each time, cut the test strip on the laser.  Label it with a fine-tip permanent marker, and store in a box for future reference.  If you do have temporary access to a calibrated laser power meter (perhaps your laser maintenance service or a sales rep has one?), record this figure on a test strip so you have an absolute reference.

The main photo shows the edge view of the test strip.  From left to right, this is the slowest to fastest speeds.  (By the way, you can see the effect the PWM and speed has in producing peaks and valleys to the cut.)

Remember--the cutting effectiveness of the laser is dependent upon many factors--tube power, alignment of optics, cleanliness of the lens, levelness of the cutting bed, and so on.  However, if you have a variety of people cutting on your laser, especially if they're cutting a variety of materials (some of which will naturally vary in density such as wood products), having these test strips can give you a more objective way of answering the question, "is this laser cutting as well as it used to?".