Diode laser cutter for foamboard - Page 2 - RC Groups
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May 12, 2018, 01:06 AM
Registered User
ccpdx's Avatar
This is not the ebay listing that I purchased, but it is the same. The TTL connection is the front connector on the right (see second photo at the top of the listing). You can see which side the red wire is on, but I suspect that they just plugged the other end of the provided power wire into it.
https://www.ebay.com/itm/Focusable-5...kAAOSwGJlZLpBz


Here's a different laser which nicely has the pin-out for every connection. And on each connection the positive pin is the opposite of how I currently have my TTL harness-adapter wired. I.e. if this is an indication of convention, then the online photos of my 808nm laser might show reversed polarity.
https://www.ebay.com/itm/Steady-200m...4AAOSwtGlZCrft
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May 12, 2018, 10:47 AM
Retired CAD guy
birdofplay's Avatar
IF the input is floating You might need to PULL DOWN the input lead with ~10K resister.
May 13, 2018, 01:37 AM
Registered User
ccpdx's Avatar
Thanks for the suggestion.

I haven't been able to play with this much more, but the other polarity didn't work. Hope I haven't fried anything. My original setup still works, so if anything's fried it looks like it's within that $21 purchase.

I did notice the Laseraxe controller board looks like it can drive up to 2.5w lasers (plus fan) directly without TTL. The 808nm laser [ebay description] says its driver uses constant current, so I assume I'd have to figure out how to set that up on the Laseraxe board before I dare plug in the laser.

I suppose one thing I haven't tried is reversing the polarity, but without the ground. I've tried it with and without the ground in the originally-presumed polarity.

Should I be able to read 5v on the TTL line if it's floating, and something less if it's not?

Charles
May 13, 2018, 09:18 AM
Registered User
ringo42's Avatar
If you are not sure of power positive and negative, you can hopefully find out which pin is ground. Find something on the circuit board that is marked, like a large capacitor. They usually have the negative pin marked. That is ground. Then use a meter to see which connector pin is connected to that. At least that will tell you which way to hook up power.
On the ttl line, you might need a pullup to 5v, that is how my laser module works.
May 15, 2018, 12:43 AM
Registered User
ccpdx's Avatar
If it can take AC or DC power input, wouldn't that suggest it's just got a built in rectifier and can take DC input in either polarity? I took your advice but I applied it to the TTL connector. I found that there's continuity between the two points I where I put arrows in the attached image, the negative side of a nearby capacitor and the TTL pin where I currently have a ground connection on my harness adapter. There's no continuity between either of the power connector pins and the negative side of that same capacitor, or the TTL pins.

Would it be worth trying completely different power supplies with separate grounds and seeing if it powers on? (Not looking at it of course.) E.g. plug a 3s lipo battery into the power connector and 3s alkaline into the TTL (in the current polarity)?

Charles
May 15, 2018, 04:30 AM
Danish? Don't U eat that??
DKChris's Avatar
An interesting bit of info is that the polystyrene raw material of the "white" foam really is clear/colorless to the eye and fairly reflective/transmissive to most of the visible light spectrum, but with a dispersive surface due to the foam "bubbles"; It just looks "white" because of the dispersed reflection of the generally white(=fairly equal amounts of all visible wavelengths combined) light.

That's also the main reason why it behaves a lot differently than white paper, as your 400-450nm(?) Lasers' light is also dispersed into the material, making it difficult to keep the light focused in a narrow cut line inside the foam, spreading the resulting heat of the part of the light that does get absorbed in a larger volume.

With colored foam, the color pigment block more or less of the light dispersion, concentrating the heat, so it cuts better. Also, a given pigment likely absorbs more of the purple light.

The 2 attached pics might help figuring out the basics of how to go about picking a usable wavelength. The colorful one is just to help keep track of how the different wavelength ranges are defined. The curve sheet is the interesting one; You want a wavelength with the highest possible absorption. The shown is for % Transmission, so technically basically the opposite, so you want a wavelength where the Transmission is minimal. Interesting bit with that is that there actually seems to be a couple of bands at the lower range of the visible part of the spectrum where this could be the case. Could look like 697nm might be interesting.

Big question naturally is if Lasers in this range are cheaper than IR ones, and if they are available at the right exact wavelengths at all. The Hitch with properly
lasing light sources is that they are literally single wavelength, so being a bit off to one side might not work, as there is no or very little energy in the "side bands" with a laser diode. You need to be within the narrow high absorption band.

Then there is the question of cutting other materials like EPP, etc. Haven't checked the absorption spectrum of polypropylene, but it might likely differ from polystyrene. And there are many other materials out there.

(Just for your info, I had a job assembling and adjusting -2W laser products for accupuncture many years ago. Those utilized a very narrow wavelength band, where the absorption of light in water and hemoglobin is minimal, in order go deep enough into the tissue to affect the cells and nerves without heating and damaging the tissue itself. If I pointed these lasers at a colored piece of plastic or paper, they would cut or melt the material quite nicely! Point it at your hand, and it would just sort of tickle a bit with the largest one. So I do know a little bit about absorption and diode lasers. It's not like I have a degree in it or anything though.)
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But to be honest, I think I'd just go KISS on it and build a simple needle cutter for your engraver rig, if I were you (Perhaps take a look at https://forum.flitetest.com/index.ph...-needle.24251/ for some ideas). To each his own, though.
Last edited by DKChris; May 16, 2018 at 07:41 AM.
May 15, 2018, 08:00 AM
Retired CAD guy
birdofplay's Avatar
OK I have to ask.

Since 808nm just OFF of the end of the Visible bracket in the chart provided by DKchris,

Is 808nm actually visible ?
May 15, 2018, 11:27 PM
Registered User
ccpdx's Avatar
What I keep reading is that your eye is supposed to see 808nm as a faint red light. That said, I'm wearing 700nm-900nm laser safety glasses the whole time and blocking my view to boot. The only way I'm planning on being able to tell whether it's on, performing well (or not) and in focus is by looking at what it did to some material after it's done it.

OK now I'll go actually read DKChris's post.

Charles
May 15, 2018, 11:50 PM
Registered User
ccpdx's Avatar
Thanks for the good description DKChris. My "15" watt is 450nm. I do plan on making a needle cutter, but the z-axis assembly I ordered is going to take a while to get here, and I really need to prioritize designing an airplane by the deadline of a vacation. I have kids and I don't have a lot of hobby/garage time so everything goes very slowly. Ultimately the KISS approach that I'll probably need to do (for now) is just cut the paper with my 450nm laser and chase it with a #11 blade. At least I won't have to cut and trace plans. I'm actually considering making a hand held needle cutter. It'd just need "skids" or side walls that go down to the right depth.

Now I also really want a ~700nm diode laser if I can find one. I wish that graph were a little higher resolution so we could see more clearly how 808nm should fare. It almost looks like it could even have a chance.

Charles
May 16, 2018, 01:10 AM
Danish? Don't U eat that??
DKChris's Avatar
Quote:
Originally Posted by ccpdx
What I keep reading is that your eye is supposed to see 808nm as a faint red light. That said, I'm wearing 700nm-900nm laser safety glasses the whole time and blocking my view to boot. The only way I'm planning on being able to tell whether it's on, performing well (or not) and in focus is by looking at what it did to some material after it's done it.

OK now I'll go actually read DKChris's post.

Charles
Sounds about right. The stuff I worked with was actually mainly in the 800-850nm range, which was very faintly visible to me when pointed at a white sheet of paper. Some were able to see it, some wasn't, so I guess there is some variance in peoples eyesight, same as some being able to hear what the dogs hear and so on.
I did however have some neat little detector cardboard tags/cards with a special flourescent coating on them in my toolset, that reacted to the range from red visible and a good way into the IR range, and were great for fast checks on function and alignment, as well as for coarsely focusing the beam at about the right distance. Usually did it at a lowered power setting, naturally, although I never did manage to damage one even at 2W output. They also come in other wavelength ranges. Can be a bit pricey, though.


On getting a plane built, just getting the plan from file and onto the foam makes up a quite substantial part of the way to a cut out kit, so simply replacing the laser with pens would also get you going. But cutting the paper as well ought to be even better. The paper edges then should act as a cutting template. It's not going to be too robust, so work carefully; and remember that you can work a straight cut by just scoring it with the knife blade, then "break" the foam along the cut line over an edge and finally cut the paper on the bottom. I mainly work with depron, and the method works very nicely with that as well, even without any paper to support the foam. Not usable everywhere, but has its uses.
Last edited by DKChris; May 16, 2018 at 01:36 AM.
May 16, 2018, 08:00 AM
Danish? Don't U eat that??
DKChris's Avatar
Quote:
Originally Posted by ccpdx
I wish that graph were a little higher resolution so we could see more clearly how 808nm should fare. It almost looks like it could even have a chance.
Missed that bit at first. When taking the table values at the bottom into consideraton, it's actually not that bad. The table says the 2 very low peaks near 700nm are 4 %T at 697nm and 13%T at 766nm. The next peak to the left is 68 %T at 841nm, but for that to be right it actually must be the peak towards lower values btw. 800 and 900nm. That puts ~800nm somewhere very close to the right of the very highest %T peak, so I'm guessing for a value for 808nm higher than 70 %T. I doubt it'll work on polystyrene.

But you can search for graphs yourself - that's what i did. Just google pics for "Polystyrene absorption spectrum" or alternatively "Polystyrene transmission spectrum". And for other materials just replace polystyrene with the material in interest. You'll note that you get a lot of graphs that look very much alike for a given material. The one I picked was just the most informative one I found on the first page. Do expect a lot of "noise" in the search results though.
Last edited by DKChris; May 16, 2018 at 08:16 AM.
May 23, 2018, 02:14 PM
Micro Boat Forum Founder
boredom.is.me's Avatar
I keep seeing "1060" for the wavelength. 10.6um is 10600nm. 808nm is off by not just a percentage, but an entire magnitude. I'm not sure if this part can be ignored or not, but most CO2 lasers start at 40W. That's 3.77mW per nm worth of energy. The same energy per nm for and 808nm would be ~3W.

The issues are wavelength transparency and energy density. I used W/nm above, but what should really be used is W/mm^2. This is determined by the lens itself. Many CO2 setups have much better focal capabilities than diodes. There is some good info here.

(I'm not at all trying to be the pessimist.)


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