RDWorks Learning Lab 102 Laser Beam Diameter

[@Gaatech]

are the mirrors in these lasers under sized. what is the diameter? If the mirror housings can be changed or adapted would bigger mirrors be an advantage in using the far extreme of the beam.

[@SarbarMultimedia]

Hi As you can see from the mode burn into acrylic, the damage diameter is about 6mm, which is the claimed beam diameter. True it probably does encapsulate maybe 85% to 90% of the energy and a 6mm beam easily fits onto a 25mm mirror. In its mount and canted at 45 degrees the effective mirror width can be as little as 14mm. That's plenty to aim a 6mm beam at . However there is residual energy right out to 12,7mm that may or may not be collected if the beam is not well aligned. I am a believer in wanting to collect it all now that I know its there to be had.The bigger problem is the fudemental design of laser head where the bore down to the lens is fine for a 3mm diameter beam 40 watt tube that they fit to these 50 watt 300x500mm machines but upgrade to a proper 50 watt tube or more and you will start to encounter design limitations. Best regards Russ

[@sccsuk]

Russ. have you ever tested the divergence of the beam from the output lens. I believe the standard tubes are actually divergent. I noticed this when testing a tube with a target 3ft from the tube the burn was much bigger than at 4" I currently run my machines with the exit windows around 30mm from the first mirror to minimise any divergence but I've not actually measured the difference between 30mm and say 60mm in relation to beam width.

[@SarbarMultimedia]

Hi It is rare that you can carry out such a test because the machine end panel is usually fixed. However, I did get the opportunity to do just that with the Bodor machine when I was in Florida. It had a fully hinged side panel allowing me to fire the laser into the distance. I was burning a spot on a card target right on the face of mirror that was oval but 8mm tall. I then removed mirror 1 and set up a target wall about 2m away. I was doing this to help align the beam combiner I was trying to fit. The burn mark was now 8mm diameter (because the wall was normal to the beam). The red dot was about 4mm diameter. This was a Reci S2 tube. So at present the only evidence I have says the beam is parallel. This current demo also indicates that I get a 12.7mm burn from a 12.7 window about 1200mm away. I think this is a Yongli tube. . I found the same fact applies to the 60watt EFR tube that I have in the Lightblade machine ie 12.7 burn at mirror 3 form a 12.7 window. There may be divergence but it certainly does not appear to show in the short laser paths that we are going to see. By the way, I cannot understand why you think the distance to mirror 1 is going to lessen any divergence. The mirrors (if they are truly flat) are only turning the beam round corners, they cannot somehow magically affect divergence. Best regards Russ

[@sccsuk]

in all my research co2 laser's beams are actually divergent from the moment they exit the tube, depending on quality of tube/exit windows etc will all dictate the level of divergence, all my testing was done with a cheap 700mm "40w" tube i was simply interested in seeing how far the unfocused beam was still able to burn material such as mdf. there was no methodology to the testing simply a sheet of mdf at a set distance and pulse the laser,. there was a noticeable change in dia of the beam as the target was moved further from the source, i believe this maybe less noticeable with the higher end tubes efr/reci as i believe they design the beam profile to be as near to parallel as possible over the first 2m from the tube, i have yet to try this with my efr tube to see if the results are replicated but the next time the tube is out or i get another one in i will try it and see, for now i just keep the tube close to the 1st mirror as standard to reduce any divergence that could be present. i was just curious if you had done any testing around it yourself. whilst he totally misunderstands the subject physics.stackexchange.com/questions/223946/how-can-beam-divergence-be-corrected-for-in-a-co2-laser-cutter did a similar test on a reci tube and found the beam size expanded over distance, yes i know he only needs to be concerned with the distance to mirror 1 not the length of the total beam path, it may well be that within the first 30cm or so that the amount of divergence is so small to be barely measurable and there for irrelevant in our context, was just a thought i had,

[@turnedoutright]

It has always been my understanding and experience that the beam diverges as it leaves the lasers aperture and the amount of divergence is dependent on multiple factors. Mirrors have no effect on this phenomenon which is a fundamental characteristic of laser light. vlab.amrita.edu/?sub=1&brch=189&sim=342&cnt=1 Lasers beams that need to go long distances can be collimated so that they have minimum size change over distance but our laser machines are not. :)

[@SarbarMultimedia]

Hi Your research is correct and in our case with no beam correcting mechanism divergence will occur. How much is debatable because I can find no specification from any reputable tube makers. There is a theoretical minimum divergence based on the wavelength of the coherent beam which calculates out to about 10microns per 10meteres. Now that may bear no resemblance to reality as it is a possible minimum but anywhere near that figure and for all practical purposes over our path lengths. you would call it parallel. I am very much a pragmatic engineer that resorts to science sometimes to guide me to practical solutions. I this case I'm only interested in whether the whole beam hits mirror 3 and disappears down the tube. If it's diverging but not oversize, I have other issues for my two remaining grey cells to deal with but I shall be getting an opportunity soon to test my tube in a straight line so I will bear in mind this topic and check beam diameter carefully at different distances. Thanks for raising this interesting topic Best regards Russ

[@SarbarMultimedia]

Hi Don Thanks for your input. Yes I understand that the beam has divergence but I'm unable to find out how much quality tube manufacturers specify.As a pragmatic engineer I occasionally resort to a bit of physics to help me out but in this case all the bits of undocumented experimentation I have done over short distanced (about 2.5m max )there was no noticeable difference between the height of the oval at mirror 1 and the diameter of the circle at 2.5m distant. If it was half a mm different then the scorch around the burn would have made definite sizing impossible.. The final crunch for me is "does the beam wholly hit mirror 3 and disappear down the hole?". It's interesting if it is diverging but has no effect on the performance of the machine.....and that's my goal to maximize performance by understanding where there are citiical settings or design issues that need addressing.. I had already visited the link you sent but I really appreciate the thought.. I did a few quick calcs (I'm no maths genius) and decided that the minimum possible theoretical divergence was in the order of 10 microns per 10 meters. If that calc is anywhere near right and manufactured tubes are in the same ball park then for my purposes thats aprox parallel. By the way I agree that divergence will not be affected by reflection from a flat mirror. You can place mirror 1 anywhere and it will affect nothing Best regards Russ

[@mryoutuser]

Great as always sir, thank you very much, very informative

[@denniskramer9788]

Better than a Cadbury Egg in my Easter basket. Thanks Russ for a very informative and professional video. Perfect timing for me to tune up the Chinese dragon.

[@SarbarMultimedia]

Hi Dennis (or are you the devil?) I have just sat down with a cup of coffee and had completely forgotten I had put a Cadbury's egg in the fridge this morning to get really cold. Now I've got to go and get it and tomorrow I shall think of you when I have to get my next size trousers out of the drawer. Happy Eater!! (sorry Easter) Russ

[@ottosouta7445]

Fantastic insight, as ever Russ. Thanks otto

[@IanScottJohnston]

Been following your vids for a while.......Could you comment, maybe in a future video, regarding laser safety. I don't see you wearing any goggles or taking any special precautions against stray reflection and your eyes. I'm just looking for info to assist the use of my own 40W laser. Thanks, Ian.

[@SarbarMultimedia]

Hi Ian I have covered this topic in an earlier session and also for my other machine kzbin.info/www/bejne/oXvIYmmPhtF8g5I kzbin.info/www/bejne/oamXp6B6nNp2r6c Best regards Russ

[@PeterEduard]

Remember that this is a heat laser. It's not a visible laser. Hence any damage to eye or skin is through a heating process, starting at the surface of the contact area. Further, the wavelength of this laser is dramatically absorbed in water, with a penetration in few microns. So while it IS dangerous, it's about on par with a column drill or alike. A stray reflection won't blind you (and only specific materials can actually reflect this wavelength). But your mileage may vary - if at all uncertain, wear a pair of (glass) googles. I do at all times, even though I find the risk very, very low.

[@IanScottJohnston]

Thanks Russ/Peter.................I only ask because I have retinal issues as it is even before I got my laser cutter, so have always been very cautious around the machine. In my workshop I have the laser cutter through a door from the PC controlling it. Helps with fumes also. Ian.

[@sccsuk]

Peter Eduard considering I have seen reflections from the steel and aluminium beds etc melt and burn holes in the polycarbonate window on the machine I feel it's very irresponsible to say that a reflected beam poses no risk to your eyes on such a public site. also polycarbonate glasses would be much safer than glass which could shatter.

[@PeterEduard]

I can only say that I have never seen that, ever. Perhaps we are talking about vastly different power of lasers? Especially if you can shatter glasses with them. The highest power I have installed is about 120W and that can't shatter glass at all. Reflections can happen I guess if things get knocked much out of alignment, but it's a quite widely (as Russ' video shows) distributed heat. I have never seen enough reflected power anywhere to mark, warp or damage the polycarbonate lid of any of my machines, ever. Never seen a mark on other surfaces either, although that would be more difficult to notice. The reflections from after the focus lens are even less of an issue, due to the spreading.

[@ΝίκοςΜουρελατος]

Good evening! First of all congratulations for your videos. My name is Nick and I am from Greece. And I recently bought a Chinese laser. Your videos have helped me a lot but I have some questions. 1. I try to connect the machine to a tablet which runs windows 10 but do not recognize. 2. When cut a piece of wood or acrylic, on two of four sides are side cut and there can align the laser. 3. When sever few stencil paper at a speed of 400mm / s when the head rises TO TOP does something zigzag. Can you tell me what can I do; thank you very much!!!

[@ΝίκοςΜουρελατος]

[e-mail]

[@thebeststooge]

Explain to me, if you can because I don't know the answer, but I have a laser pointer (5mw) and when I pointed it outside my window to an object 50m away the dot had grown pretty large. Is this because it is only 5mw or what is going on? No mirrors for distortion so stumped I am.

[@SarbarMultimedia]

First I have to say I have no rational explanation for you. There will be double refraction as the beam passes through glass ie the beam will come out of the glass at a point that is offset to the entry point but the entry and exit beams will be parallel. So this cannot be explain what you are seeing . Glass can be very a complex material depending on its constituants and how it is made There is usually very little crystal stucture in glass otherwise it would not be transparent. It may be possible for the few crystals that are there to cause scattering of the beam as it passes through. I would experiment with some cheap picture frame glass to see if you can replicate the result. You could also write to the tech department at one of the big glass manufactureres. I also need to apologize for not answering another of your questions. I looked back and was a bit confused about which one I had missed. Was it the stainless engraving question? Best regards Russ

[@ottosouta7445]

Your 5mw pointer is Laser Diode, quite different from our 50-80W CO2 laser tube. There is usually lens in front of the LD, which can be focused by turning the barrel. The LD has so called Fast Axes, which creates oval shape of the beam, usually corrected by FAC lens. On more powerful LD you actually get a line instead of a spot. I am talking about output of 4W and more. And than there is the glass interference, as Russ mentioned earlier. regards otto

[@thebeststooge]

Yes, I understand that but why would this laser grow the farther it goes? Laser is supposed to be a coherent beam not like a flashlight regardless of what is producing the laser.

[@thebeststooge]

Russ, it was the stainless. As Otto mentioned I have a laser diode but a laser is a coherent beam regardless what is producing the beam (solid state or gas) so the farther out the beam goes the bigger it becomes which makes no sense to me for lasers. If this were a simple torch (flashlight) I could understand.

[@SarbarMultimedia]

I can only take an educated guess at your laser pointer problem by saying that I agree about a coherent beam of light and those photons are all happy to travel as a tight knit group until they hit something. That something could be dust particles in the air, rain, fog ,snow etc and then they start start losing their energy and probably being knocked off their straight path. For artillery range finding they use kw lasers not milliwatts to try and overcome this issue. As I mentioned, glass may appear transparent but if there is any crystal structure within, then those crystals would steer the photons off course. Now please understand, this is just my logic and not verified fact so I cannot really unravel your particular question. As for the stainless question, I must apologize for missing it. However, it's good to answer it in this comments section because as you will see in my beam energy profile picture, the higher the energy density of the beam (towards the centre) the high the temperature. With my 70 watt beam I can already see about 1500C before it passes through the lens where the energy density (temperature) will be further magnified. Stainless melts at about 1450C so when you stop and think about it, there is potential to damage the surface. However, the initial problem that you have to overcome is REFLECTION. The crystal structure of stainless steel makes it about 90% reflective so chucking 1500C at the surface is not going to cause melting because most of that heat energy will be reflected. That's why I was a bit hesitant about this whole venture. The good news in my case is that with 60 watts amplified, I am hitting the surface with so much heat, I can overcome the reflection issue and start melting the surface, As soon as that happens then the crystal structure changes dramatically and the surface become absorbent to the heat , but only very locally because now the thermal transfer properties(and mass) of the steel come into play and the energy gets quickly dissipated, thus limiting the depth of the melt. After all it is only a pin prick of energy that might be incredibly hot but at 60 watts it has no hitting power. I doubt if a K40 (30watttube) would ever be able to genetare high enough spot temperatures to overcome both reflection and thermal conductivity. Best wishes Russ

[@jimmybleron4700]

great work thank you Ross!!!

[@BennybumfIuff]

Hi Russ. Over the last few months I have spent many hours watching your videos , I owe you a huge thank you. I finally received a squashed Chinese laser printer. I know this is off topic but the chassis is twisted about 10mm. Looking from the front, the black chassis rail and the laser head bearing rail have a 10mm twist. The seller assures me this can be fixed. I disagree and demand a full replacement or refund. Am I being fair? I can email a photo if it helps you understand what I'm trying to explain.

[@SarbarMultimedia]

Hi A bent chassis can be fixed by a force in the opposite direction to where it took the hit. However, it would take a very skilled fabricator to attempt that work and even then there would be no absolute guarantee. I would take photos of the damage and continue your pursuit of the vendor but if you bought be credit card you will be in a stronger position. Keep records of all the correspondence you have with the vendor and his negative replies. Let the vendor know that you will be approaching your card supplier for a full refund and to be honest I would be contacting the card supplier right now and find out what evidence they require. That may trigger a response from the vendor, although I doubt it.. If you are successful with your refund appeal you will probably finish up with a free but broken machine. What can you then lose if you try to fix it? All good luck Russ

[@BennybumfIuff]

SarbarMultimedia thank you for your quick advice. Exactly what I thought.

[@dom7ism]

bonjour....mon laser 150w home made est monter...que pensez vous de mais coupe acryl 8mm salutations..."dom dirc" sur you tube

[@SarbarMultimedia]

Bonjour Dom Mon français est très basique mais je pense que je comprends votre question. J'ai comparé ma traduction avec la version de Goole et nous sommes presque d'accord. Je pense que vous demandez de couper 8mm avec votre machine. 150 watts est beaucoup d'énergie et avec n'importe quelle lentille de focale devrait couper. L'acrylique est un matériau étrange car il ne brûle pas comme des matériaux organiques tels que du bois ou du cuir, au lieu de cela il s'évapore et se transforme en fumée. Tout comme la vapeur, ces vapeurs se condenseront sur des surfaces froides (votre pièce de travail) et laisseront une brume trouble sur la surface qui ne se détachera pas ... Il n'y a pas de réglages fixes pour votre machine car cela dépend de votre puissance, de la distance focale de Votre objectif et l'efficacité de votre assistance aérienne. Si vous voulez la vitesse de coupe la plus rapide, seule une petite quantité d'assistance aérienne est nécessaire. Cependant, cela va pousser ces vapeurs vers le bas sur la surface de travail, à moins que votre flux d'air soit directement dans la coupe et le soufflage des fumées en dessous. Pour obtenir la coupe la plus douce, vous devez couper à 20 à 30% de vitesse plus lente et tourner l'air à presque rien. Pour un tube aussi puissant, vous pourrez facilement utiliser un objectif de focale de 2,5 "ou 4" pour obtenir un joli bord droit et droit. Ces choses techniques sont bien au-delà de mes compétences linguistiques, alors j'espère que Google effectue une bonne traduction. Si je n'ai pas répondu à votre question, écrivez à nouveau Tous les meilleurs voeux Russ

[@Mentorcase]

I thought for a second there you were going to disable comments, thankfully no, disabled comments always get a thumb down from me.