Laser Cutter Focus/Defocus Calibrator

For a lot of the time between 2014-2020, I was a frequent flyer, member and volunteer at Maker's Asylum, one of Mumbai's only makerspaces.

On the lasercutters I frequently used, the focal length - or more precisely, the distance required between nozzle tip and material surface - changed on occasion for various reasons. A new lens, some overhauling, thorough cleanup sessions, not screwing the nozzle properly back in - all this and more get in the way of having a crisp cut. On the flip side, sometimes you wanted to use a de-focused beam with a slight width to scan better. 

So, I came up with this jig that allows the beam to run down a surface sloping at 30 degrees, catching the cone of the beam at all heights. This makes visible the beam width and it's variation across different heights. It is very easy to measure the point where the focus is best, and because the slope is 30 degrees, the focal distance is simply 1/2 of the measured length, by trigonometry.

Initially I created this as a lasercut jig itself, then later made a 3d printed one, and finally, in a mix of wanting to use the sheet metal module in Fusion with some nice ornamental “graphics”, I created the current version, especially the elven decor one.

Find my original Hackaday page for this here, with detailed how-to-use, etc.
https://hackaday.io/project/160647-lasercutter-focus-calibration-jig

How to use :

• Take a scrap strip of a material. Alternately, use the attached test strip print, ideally with a masking tape or painters tape on it to save the print from damage.
• Lodge it in the jig such that it's free end extends up on the high side. The test strip has "ears" as well to locate it on the jig.
• Place the jig with test strip on the laser bed, aligned left-right, i.e to the x axis
• Adjust bed height so that the nozzle barely touches the edge of the test strip
• Run a drawing of a single line, or use the pulse button, depending on your machine, and draw a quick straight line along the test strip, which will leave behind a burn mark of varying thickness
• Measure the narrowest point of the beam from the start point of the beam, divide that by two, and you will get the desired distance between top surface of material and nozzle tip.

You can also measure to the point where the beam diameter is what you would require to etch a line font, line art or a scan “fill” such that the line is actually thicker and the effect is what you precisely desired.
 

The calculation is simplified by the fact that the slope of the jig is at 30 degrees, and so the vertical distance, “y” should be ½*hypotenuse, i.e. measure the length and divide by 2.
 

After the lasercut (and wood cut) versions, I created a 3D printed version at some point. I have attached a plain file as well as one that is styled after the elves of Middle Earth, because why not !

Design notes:

The “Elven” version is pretty. The plain version is still graceful. I decided that after the straight line versions I'd made with lasercutting or wood, the 3D printed version should be something that the other two can't easily be.

Print notes :

Print with the side flat on the bed for best strength. Nothing else that particularly needs to be taken care of.