Laser Cut K40 LED position indicator

Last crawled date: 4 years, 4 months ago

This is a device to help position your laser beam precisely and repeatably, regardless of height of material, focus, or coordinates. Unlike head-mounted laser pointers or beam combiners, it does not add any weight or complexity to the head, or reduce the beam's power. It also helps in finding a rough focal depth.
I didn't invent this; this is just my laser-cut version of an existing design by scorch and before him, Peter Jensen. I don't have a 3D printer, and I thought it was appropriate that laser cutter owners should be able to make this, which should also be a lot faster ;) It's also made from parts so you don't have to destroy a flashlight.
Scorch's video about his version is here, which covers the theory and installation: https://www.youtube.com/watch?v=r4GfdS4GDqs
Required (adjust as you like):
4x 5mm clear LEDs (not diffuse), they don't have to be superbrights but that would probably be better.
a 1k resistor (calculate your own value if you use different LEDs or source voltage)
wire, and ideally connectors for the 24V tap
a magnet or other method of attaching to the frame (I used a hard drive magnet)
soldering iron, solder and basic skills
probably a hot glue gun
I added a connection to the end of the internal LEDs that came with my K40, which are at 24V. It's generally not advisable to add any load to the stock power supply, but these only use a tiny amount of power. Superbrights may be different. I used a two-prong connector so I can disconnect power or remove it entirely.
The LEDs are wired in series (shorter leg is ground) around the loop (don't connect the loop!), the resistor is on the ground side. Use heatshrink to keep it from shorting on the case. Glue the ring onto the base part so it's raised and won't short or catch on the edge of the hole.
It might slide down over time with vibration, though it is easy to re-align, so you might prefer velcro or whatever, just make sure it can be removed for laser/mirror re-alignment.
Alignment: start by powering the LEDs and position the ring in the middle of the beam hole. Move it so you can see all 4 LEDs on the material. Do a test fire so you can see where the beam hits. Without moving the head or material, adjust the ring until it "targets" the hit point. This is somewhat tricky as the image is reflected and reversed through the mirrors and lens. Try covering one LED at a time to see where that lands on the material and move towards/away from that.
Focus: this can give you a rough idea of where the focal point is - you simply move the material or lens holder up or down until the image of the LEDs looks sharpest. This is not perfect because 1) the LEDs are a short distance away from the actual beam origin, and 2) for cutting, you want the focal point in the middle of the material. You can just move the head/material closer to correct this, but if you have a measurement tool, just use that.
Possibly improvement: try to mount the LEDs around the actual laser opening, so it will be more accurate, and won't shift!