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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.
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