Laser Focal Length Aid

thingiverse

Building on a YouTube video by Patrick Hood-Daniel, "blackTooth Laser Cutter/Engraver - Determine Nozzle Height for Optimum Focal Length" I wanted to create a 'jig' to hold my material at a set angle and use a wedge of the same angle to easily measure the distance from the laser nozzle to the point where I determined to have the smallest kerf. I cut this object from 1/8" black acrylic and tapped the holes for M4x80 spacer screws. I then glued the small triangles, cut from the side pieces, into a "wedge" using "WELD-ON" brand acrylic cement. The wedge has the same angle as the jig. To use it: 1. Place your material of choice on the jig and position on laser bed. I used a 3.5" x 6" piece of chipboard, which is cheap and marks well. 2. Adjust height of nozzle/bed such that the estimated focal distance is approximately halfway up the ramp. Also make sure the nozzle will not hit the material in the next step. 3. Set the laser to engrave a 150mm line, running up/down the ramp. The engraved line will be wide at the top and bottom of the ramp but very thin where the material is at the optimal focal distance. I used 50% power and 200mm/sec. 4. Using your calibrated eyeball, mark on the ramp where the engraved line is the thinnest. 5. Place the "wedge" on the ramp with the sharp tip at the marked position. This will create a level surface from which to measure your nozzle height. 6. Position the laser nozzle over the wedge and measure the distance from the wedge to the nozzle. I used a telescopic gauge and calipers. 7. Finally, you can cut a new focus tool out of your material of choice using the optimal height measured in the step above. As I suspected, the nozzle height gauge that was shipped with my laser was a little off but not too bad. The factory gauge measured 19.63mm, and by using my focus aid, I determined the correct height to be 19.02mm.