Maybe a new alignment/positioning aid/concept

This thought came to me while waking up over coffee, so be gentle…
Aligning a CO2 laser is difficult because of the high power and invisible beam. Inserting a coaxial visible laser in the center of the beam with a beam splitter makes things easier. But beam splitters are expensive, and ensuring that the visible beam is coaxial is a problem.
How about putting three visible beams parallel to but outside the CO2 beam? If you ever once got them parallel and “encircling” the CO2 beam path, they would stay that way for meter or so of the longest beam path in the machine. That being the case, the visible lasers alone could be use for alignment. Further, if the lens transmitted their wavelength, the three would converge (or nearly so, depending on chromatic aberration in the lens) to a near-spot at the focus distance, usable for rough focus depth setup.
There are reverse-boresight devices that put a visible laser aimed backwards through the lens mount to align the mirrors back to the tube, but they aren’t any help with focus.

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This might interest you.

As I see it the problem with alignment is knowing where the beam is in 3D space relative to the gantry.
The most difficult alignment is when your tube is not parallel to the gantry and the beam exits the first mirror at an angle relative to the gantry.

This set of tools is referenced to the gantry and give you the ability to see the beam in all axis, x and y along the beams path.

By placing a target that is referenced to the gantry in two locations along the path you can see complex misalignments pretty easy.

I have only used this setup a few times but found it pretty easy to align the beam all the way to the surface.

600nm is still a bit different than 10µm so I’d expect some impact from chromatic aberration, but it would be an interesting experiment.

I had been assuming a combiner in the DIY design I’m playing with, but had no intention of using it as a mirror alignment aid, only a stock positioning aid. And I was pondering that vs. two laser line projectors (which I assume are cheap but I haven’t looked) that converge in the line of fire. But neither would give the focus benefit.

However, how would you get the lasers close enough to be along the edge of the CO2 laser beam without damaging the LED laser devices which are wider than the beam they produce?

@Don: Yes, tools to ensure planar parallelism in 3-space would be great. I have done a little bit of amateur machining, so my solution to this was to shim/align the Y and X axes with a dial indicator. Overkill for the K40, but it was simpler to me than other things. Mirror and optical path alignment got much easier then. But the idea of aligning the mechanical axes to the bottom of the machine (which is, itself, not a plane) is foreign to most K40 users, as your experience attests. And not many people have a dial indicator lying around. :smiley:
The reverse-boresight deal is probably the simplest K40 add-on for alignment, although it has its own problems. It’s probably a great tool for coarse alignment though.
@MIchael:
We do know that ZnSe lenses transmit visible red. Otherwise, beam combiners would not function, so that part works. I know that chromatic aberration would be a problem, I just haven’t researched how much it would be. It’s certain that the 10.6um laser beam would not focus at the same distance as 590nm red, for instance, but I don’t know how far apart that is. If it’s a mm or two, it’s a useful coarse focus, maybe. Maybe.
As for getting the red beams close to the edges of the CO2 beam path, I speculated that a pair of small mirrors forming a mini-periscope would work. Something like a chunk of clear acrylic tube with the ends cut across at 45 degrees, and a bit of front-surface mirror glued to the openings. A bit of a pain to start with, but do-able. Hmmm… better yet, 3d print the mirror holders. The exit mirror could be quite small, and mount quite close to the CO2 beam path edge.
I think the harder problem is fixing the boundary beams solidly to the CO2 tube so they’re referenced to the beam exit, not the case. That’s one of my issues with beam combiners - where are the references? The case is a bad one.

I went off to see if small first surface mirrors are even possible. It turns out, yes. Here’s a link that sells a sample of first surface mirror in acrylic that’s 6" x 6" BY 1/8" thick for $15.

That’s enough for a LOT of small mirror tidbits. Now if we only had some way to cut 1/8" thick acrylic sheet… :slightly_smiling_face:

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My experience is; all that matters is the beams alignment with the axis of the gantry.
I ignore the machines frame etc. and reference some carefully cut pieces of acrylic with precisely registered targets. Could be laser cut of course.

The optical ideas I have tried turned out to be just as hard to adjust as the machines optics and you have the key question of which one is right.

Yeah, I wasn’t doubting visible red transmission.

The beam combiner I was planning to get if I go that route has the same three-point adjustment as the normal mirrors. I was planning to put it between mirrors 1 and 2.

Good luck 3d printing something accurate enough to aim the mirrors though! :slight_smile: