Laser Engraver Ring of LED's to indicate laser position

This is my rendering of a locator for a CO2 laser engraver. Simply position the ring of LEDs around the beam after the first mirror and you will see the spot is casts on your workpiece.

It does not help with the focus, just with showing you where the laser will burn in a large spot, about 2 or 3mm diameter.

There are a few other designs on Thingiverse, have a look at them too.
scorch's LED Ring Laser Position Indicator
jdbyrnes' Laser Cut K40 LED position indicator
and mitchel_cj's K40 laser light guide
A very nice demonstration 4 dot laser cutter position indicator

This design uses 8 white LED's in a small ring. The "spider" has 10mm magnets to hold it to the large hole at the back of the K40 type engraver internal wall where the laser leaves the first mirror. You can move it about and if you stick some painters tape to the cover you can get the laser nicely in the centre of the ring with a scorch test.

There is no PCB required, just connect the LEDs in series after pressing them into the spider. The flat side pin of one LED always connect to the round side pin of the neighbouring LED. You can get creative with putting them in 2 groups of 4 or dropping one LED then powering it from the K40's 24V power supply but I wanted it totally separate so as not to affect the reliability of what's already a somewhat shakey system.

I suggest you roughly locate the laser beam before you position the ring and then do a more accurate centering.

The LEDs need about 24V to start working but aren't that bright at this current. I use 28V to get a very bright ring of light. To get the 28V I used a cheap boost circuit, search for "MT3608" from one of the many online electronics modules suppliers. Supply it with 5V from any phone charger and the output is 28V or whatever you set yours to. Just be warned, it takes a lot of turns of the trimming pot to get the module voltage to start changing. Here’s a video on adjusting it without damaging it. There are a few other enclosures on Thingiverse for the MT3608, do a search to see if you can find one you prefer.

Route the cables nicely so they don't get trapped in moving parts or cut by the laser.

The LEDs are all in series, I included a 33 ohm resistor in the LED circuit to make the current less dependent on the LED forward voltage. At 20mA the resistor will drop 660mV and will not get particularly hot, a 1/4W or even 1/8W resistor will provide ample dissipation. I ran mine overnight as a test. I suggest you buy a long USB charging cable to power it if you leave it inside the K40.

I made a small case with a lid for the MT3608 boost module to protect the module from external contact, it leaves the adjustment pot exposed so you can adjust the LED brightness as you see fit. Mine is a little too bright and the circle is a bit unclear as you can see from the pictures. You don't need this case, the MT3608 is hardly working and doesn't even get warm, you can just shrink some heatshrink around it if you're lazy.

You can see that the spot is quite bright even in a fully lighted room with the K40 LED strip on.