K40 Laser Beginner Insights draft document from FB K40 group

This isn’t directly on topic, but it may be useful to you. When I was setting my K40 up I went off and pounded the internet for references, studying Don’s web site among others. One of the low information content sites I ran into was the facebook group on K40s. There were a few nuggets there, but mostly people brand new to the K40 firing off the same beginner questions repeatedly, and getting one-liner answers. This really bothered me. I think that once you find out how to solve a problem, you WRITE IT DOWN so the next guy doesn’t have to dig as hard to solve it. So I started collecting the beginner questions and wrote down the answers, posting it in the files section of the facebook group.

This worked out as well as you might think - it hardly reduced the beginner questions at all, as no one appears to scan the files section at all until they’re told to go read it.
Sigh. :slightly_smiling_face:
Anyway, here’s a link to that file. The beginners have been very happy to read it when I tell them to go do so.


I do not frequent the FB site for the reasons you outlined.

Folks there: do not do their research, want an instant fix, provide inaccurate information, do not respect experience, want to argue with responses, operate in unsafe environments etc.

I, like many on this forum, have been helping folks fix, maintain, adjust, upgrade K40’s for multiple years. We all have tried to prevent users from rediscovering a common set of problems but to no avail. I have even written troubleshooting guides that pretty much go ignored. Seems like every new user is compelled to drag themselves through relearning past experiences.



Yep. It makes me nuts and I have to stop myself from ranting. Facebook’s “society” collect people who only want one-liners, not learning. Sad.
By the way, thanks for your web site. It was really good for me. I do a lot of electronic design, and am in the (continuing) process of setting up a Pi to control the K40, integrating the flow sensors, temps, current watching, and so on. Your documentation of the power and cabling was a huge head start on that.

Again, thanks.

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Your welcome and glad it is helpful.
By now I assume you have found the schematics?

Yes, I did. Nice work sussing that out.
I was especially interested in the detailed schemo because i used to design switching power supplies for a living. The controller chip was familiar to me from that time.
It’s a little quirky in that it runs the high voltage in current limit all the time - the pot sets the current limit - but apparently that does work.

@keen any chance you would be willing to upload the PDF here for those of us who don’t use facebook at all? Maybe in a new thread that we can link to from the category sticky post?

The link posted a few posts up should work. If it doesn’t, let me know. I actually tried to copy it here, and didn’t find a files section to put it in.

The link doesn’t work for non-facebook-using folks like me, sorry.

There’s no “files section” — that’s not a discourse thing. Just use the “upload” button in a post. If you could do that in a brand new post in the #k40 category that would be wonderful! :slight_smile:

OK, didn’t realize it would not link.
K40 Laser Beginner Insights 1Feb20.pdf (86.4 KB)

Does that work here? Don’t expect wonders, it’s just a concatenation of stuff, but maybe it’s a useful checklist

By the way, my impression of facebook is that if you have to do it, you should do it behind closed doors and wash your hands afterwards. :laughing:

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No, sadly, that’s a lot of facebook HTML, not a PDF document, despite the name. It starts:

<!DOCTYPE html>
<html lang="en" id="facebook" class="no_js">
<head><meta charset="utf-8" /><meta name="referrer" content="origin-when-crossor
igin" id="meta_referrer" /><script type="text/javascript" src="https://ff.kis.v2

Ooops. Trying again, found my original PDF.

Again, let me know if this doesn’t work.
K40 Laser Beginner Insights 1Feb20.pdf (934.8 KB)
It’s weird that just because I’m a facebook member it “grabs” the file in its own format. Just goes to show the evil, I guess.
Additions and corrections welcome.


That works great! I’m looking forward to reading it in more detail; it looks like you put a lot of work into it.

What would you think about turning its contents into a large, cooperatively-maintained pinned post here, that we can then link to from around the internet? It’s your call since you wrote it, but I’d be willing to help set it up.

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@keen looks great.
I would add more to eye protection. Users simply ignore the possibility of damage to their sight.

As you may have summarized by now I am stubborn about getting folks to add safety interlocks, which I see as a critical upgrade to do before you run the machine.

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@Mcdanlj: I’m good with that. It’s not just a facebook thing. It probably needs me to add a set of links to web sites with the much deeper information I synopsized there. I really meant that additions and corrections are welcome. I can’t tell you how much I wish something like this existed when I hauled my used, crippled K40 home to resurrect.
@donkjr: I agree, it needs more on self protection. I kind of gave up on adding more stern warnings. On facebook, the only criticism this file ever received was from a guy who thought it was too gloom-and-doom.

I have two papers I put up there on cooling, boiling down (… sorry, couldn’t resist) the cooling issues that appear from every single K40 newbie in facebook. I also have a nascent paper on fires alone. It’s a concatenation of the posts that appear there that start “I only walked away from the machine for a few seconds and this happened…” along with pictures of the fires that resulted. I’m good with putting those here as well if you’d like.

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As a side note:

I added a thermal sensor to the head that is in the interlock loop as a stab at preventing a bad fire. Side benefit; it monitors the cabinet temperature (but who cares).

I have no idea if it would be fast enough to protect anything as I have not had a fire and I never leave the machine unattended. No idea how to do a nondestructive test of a catastrophic event.

I also have this in que https://amzn.to/2vq2Fgi to test someday. However I am expecting it would detect the laser in normal operation as a fire.

The files are only the tip of the iceberg for me. I’m actually accumulating other update/design items for inclusion in “The Ultimate Update” (said with echo, like on the radio). One of the items is an exhaust vent temperature sensor. I have a friend with an Epilog, and he walked away for a couple of minutes, a fire started, and the Epilog was a total loss. We’re both veteran electronics engineers, and the best we could come up with for sensing a fire was an exhaust temperature sensor. Optical flame sensors just look too wonky to be reliable.
He’s in favor of using a DS18B20 in the exhaust air, but I think that’s too slow (~750mS per reading) and think that you need to go thermocouple, which is effectively instantaneous for things like this. A Raspberry Pi Zero W is ~$10, and would be a great thing to just use for monitoring, if nothing else. We’re headed down that path now.
We have this ongoing design argume… er, discussion, on whether you could effectively quench a fire by valving CO2 from a cylinder or CO2 extinguisher into a perforated copper pipe set into the front of the laser’s cabinet to quench things. Other options are turning on a water mister to quench a flame. What we really need to do is find a used, dead K40 for cheap and use it to start internal fires to see which detection and quenching schemes work.

Sigh. So many designs to do, so little time.

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I think it would be an excellent idea to have cautionary tales here. I’m strongly in favor.

I would expect it to take some time for the air in the cabinet to get to an over temp and then a temp sensor to respond before the ignition of something.

I think filtered optical sensors would work if they were positioned in a way to see a flame but not the beam. Still sketchy …

My frustrated attempt is to get a sensor close to the head hoping that it could detect a high heat.

Lots of reasons this won’t work:

  • To slow
  • The beam starts a fire but then as K40 is cutting the head [and the sensor] is moved away from the fire and does not sense it.
  • The fire starts instantaneously once it’s started sensing that its started does not prevent damage only provides a warning, but maybe it keeps from burning the house down :(. This is where an extinguisher integration would help.

Takes you back to this realization. These are dangerous tools to have in your house, just like a welder, torch, table saw, CNC etc. Do not operate them without supervision, common sense, self protection and proper training.

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Yep, all true. My niece was familiar with CNC lasers from her architecture degree labs, and bought a Full Spectrum as soon as she could afford it. She told me a lot about her learning curve.
Her point is a variant of what you just said: people buy these things thinking they’re an appliance, like a coffee maker or refrigerator, not knowing that they are really automated tools that need technically-accurate setup, alignment, maintenance, software setup, and surrounding-area modifications to run for any significant amount of time. People who don’t have either the technical background or the willingness to learn quickly should not be buying them thinking that they’ll just go make easily.

My reasoning on the heat/flame sensors was much like yours. There is a vaporization, minor flames, and a very, very hot spot inside the K40 cabinet all the time. Sensing vapor and fumes (ala smoke detector) won’t work, because there is supposed to be vapor and smoke in there. Sensors that look at the beam target spot will of course see high levels of both near and far infrared - that’s how it works. I went after excess heating in the exhaust stream.

We know that the laser delivers (at most) 40W to the air in the enclosure. The tube’s cooling water removes about 160-200W of heating (I came up with this in the cooling files I haven’t yet posted here), and there is some cross-ventilation from sucking air from the power supply section, maybe another 20-30W. One ought to be able to figure the air mass flow rate, calculate the temperature rise of air in the throat of the exhaust vent, and set a temperature threshold where getting hotter than that requires burning fuel in side the laser cab - a fire.

I’ve also speculated about doing a two stage extinguisher, the first being a water mister, coming from web sites from colleges where they require not only watching their lasers in labs, but also keeping a water spray bottle ready to extinguish small flames before they can grow. After that, you’d valve in CO2 to smother the flames.


Here’s a thought - anybody know where we can get a stripped out K40 cabinet to test fire suppression techniques? I dimly remember seeing cabs for sale somewhere.

I’d be good with making the sensing electronics to test if someone has a cab.

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