RDWorks Learning Lab 162 Lenses part1 Let's Focus

[@SarbarMultimedia]

To anyone that watches this, it is now several years old and my reserch into the way that lenses and laser beams work has moved on in leaps and bounds. This video investigates the fact that the OPTICAL focal point appears to move with speed. I now know that there is an OPTICAL focal point that results when lens geometry, focuses NORMAL uniform random light through a small spot for IMAGE projection beyond the focal point. However, laser light is not random or of uniform intensity and has no image to project. It's work starts and finishes at the focal point. These Gaussian intensity light rays are refracted exactly the same as normal light by a lens BUT this time were are employing the INTENSITY of the beam to damage material and that INTENSITY focus is the the feature that changes with speed, power, and material being damaged.. There is so much more to learn.

[@jameswares4469]

Nice to see you back. Very interesting looking forward to the next one 🥃🥃👍

[@alprivate811]

Wow. I have to contradict you. You are a natural instructor . As a technical director at a high school for many years I can say your lecture , drawings and charts were captivating and many teachers would love to have your skill. Thank you as I learned a lot about the optics.

[@SarbarMultimedia]

Hi Thanks for the kind words. As I say, the lens is the most important part of our machine and it appears to be one of the least understood elements. I did college level physics and chemistry and a lifetime in engineering has further focused me into learning more about narrow areas. With much deeper recent research into optics I am finding it difficult to make theory and practice match. I am further frustrated that I can track down almost zero scientific research on the peculiar way that light energy reacts with materials during the cutting process after passing through a lens. There a a couple of great publications that I have studied during my time of owning a couple of 3kw metal cutting lasers but that theory does not apply to these non-metal cutting machines. Metal cutting is dependent upon high pressure oxygen or ultra high pressure nitrogen assist gasses for the cutting process to be successful. This initial foray into lens behavior has made me realize I need to understand so much more. I think this exploration will take many more than 3 sessions Best wishes Russ

[@CCCfeinman55]

Very nice. I enjoy your clear, explicit and “common man” quality of your explanations. That makes this highly technical stuff far more accessible to everyone. It might also serve to point out that the total power within the beam is distributed across the area of the beam at any point, in a Gaussian curve, and all beam diameters. In short, the total power remains almost exactly the same as the area under the curve of distribution, but consequential to total area. And of course, total energy delivered to any one location is always a function of how long the beam “rests” at that position. Finally, the difference between the hole made by the converging beam (a) suggests a broader, Gaussian energy distribution, as compared to the divergent beam holes (b and c), which do not appear to be quite Gaussian distribution. Looking forward to your next installment share and what conclusions you draw from the data.

[@chuckterra6375]

Great explanation... indepth, concise... good job 😊

[@QuinnHale]

Russ, your videos are like a warm, familiar blanket. Thanks for being you. It's not a given. Thankfully you've chosen to be who you are. What I'm really saying is "Can you laser a blanket?".

[@SarbarMultimedia]

Hi Quinn The answer is yes. Lots of dense smoke and a vile smell Best wishes Russ

[@MR-hc9uh]

Sir i appreciate the way you explained and your patience to make hard heads like me to understand how this actually works. Thank you so much. God bless you sir!

[@Runner50783]

Thanks for all you do Ross. The knowledge you are spreading is invaluable.

[@scottinharwood]

Is there not an acceleration factor for bringing the laser head movement up to its travel velocity and then slowing it down at the end of the run and could that be what you are running up against? I would think running the 10mm slope over the length of the X-axis might show a better or more consistent focal point position?

[@SarbarMultimedia]

Hi Scott You do indeed bring up a very good point. Yes, it does take more distance to accelerate the head to faster speeds. However I think you are imagining that acceleration to be slow and the reason for variation of focal point with speed. However, If you lay the material flat then there is no focal variation involved. What you will see ( as I think you anticipate) is a thick line as the head starts from zero speed and it quickly becomes a constant thickness line until you slow down, whereupon the line gets thicker again as it decellerates. At slow speed this acelleration phase is about 3mm and at the fastest speed I used it's about 20mm. The key narrow parts of all tests were well away from this acceleration region. As I move forward with my learning journey, always remamber these are not tutorials by some expert. I am still a student who is self-educating himself about the minute details of this technolgy. I am sharing my journey for others to observe. Yes I do make mistakes (that all part of learning) but I try to correct them in future sessions. However in this session I did show that the ramp test must be used carefully but did not undersatnd exactly why this interesing anomoly was occuring. It took another 2 years for me to fully decode why. It turns out that speed, power and material type can put the focal point of a lens as much as 4 or 5mm diffent to the manufacturers designed focal length Best wishes Russ

[@isettech]

When I bought a 2nd hand Chinese laser with no data on the supplied lenses, I performed a similar test but instead of attempting a narrow beam, I used the manual power to engrave a rectangle on sloped wood. Turned the power down as far as possible while still getting a mark. The theory is when out of focus and at low power the power density is too low to mark the wood. Therefore at very low power, only the area in sharp focus had enough power density to produce a mark. This is how I found the focal lengths of my 2nd hand lenses. I just made focus spacers for the nozzle to work space for the two lenses.

[@SarbarMultimedia]

Your method is perfectly valid and it will determine what I would have prevoiusly believed to be the focus point. This session shows that you can never be certain of the exact focus point The manufacturer claims one focal distance but we have no idea how that figure was arrived at. The the static tests as I mapped the beam shows large variation from specification and then there is the addition change of focal point with velocity.. Hmmm...who said this stuff was simple??? Best wishes Russ

[@MiscRocketVideos]

Very interesting presentation and observations. Look forward to watching all your past and future work!

[@actiontower]

What an outstanding tests, Thanks for all you do sir.

[@ViniciusMiguel1988]

Hello, I think the reason that you can get shorter pulses when the machine is running is because the laser is warmer and the gas is more excited.

[@sto2779]

52:49 - That's really an interesting question... sounds like bull to me too from what the pros says... Do you get the same results for all different sizes of diverging lens? if thats the case... then it means the pros needs to reevaluate about their understanding of optics and laser beam.

[@SarbarMultimedia]

The optics companies only have one goal and that is to focus all the light to a single point. That is the standard against which all lenses are judged. All Chinese lenses for these machines are very simply made with a spherical surface. on one face and usually a flat face on the other. This produces a poor quality focus and would be abysmal for photographic work because of a natural effect called spherical aberration. This can be reduced significantly by adding an additional focusing shape to the other face of the lens, a concave surface. This is called a meniscus lens and is about as complex as we can buy Better focussing for visible light lenses can be achieved with aspheric lenses.. No such fancy gear for us. BUT...do we need it Crappy cheap Chinese plano convex lenses may be laughed about in "proper" optical companies but they cat at least 30% better than the more expensive lenses. Why? Well I am convinced there is a weakness where the the power is poorly focused just around the central axis of the lens. This is because the spherical face is almost normal to the lens axis and very little bem refraction occurs.. This also just happens to coincide with the most intense (powerful) part of our Gaussian laser beam. Seems like the perfect marriage to gain more cutting power from the lens. Lots more work to do on this and you will see my progress from time to time as you continue following my learning journey. Best wishes Russ

[@shbyshby]

There is a problem with focal length calculations, the focal length of a lens is measured (not calculated) by the focus position when the light comes from infinite distance, but when dealing with macro or close focus it is best to calculate it by measuring the distance between subject and figure when magnification is 1: 1 and F is the distance between the subject and the figure divided by 4

[@SarbarMultimedia]

For my first few years of using this technology I was happy to assume that the conventional lens theory that I had been educated with and used as a photographer was equally applicable to laser light. However as I tried to decode the odd behaviours of different lens shapes. orientations and focal lengths I discovered that conventional lens theory is not applicable. Yes, the focus rule you quote is applicable BUT the light entering the lenses is not uniformly distributed as in the normal light world. Laser beams are very non uniform and the intensity is usually a Gaussian distribution. Because the damage you inflict on materials is directly related to light intensity, it means that although the outer diameter of the beam defocusses away from the focal point the central core of the beam has tremendous power (intensity) way above and below the focal point. This is best proven (if you have a laser machine) by observing the fact that the line thickness or apparent focal point changes with speed and/or power. Fortunately conventional white light lenses do NOT change focal length with light intensity and that is why normal lens theory works for a uniform light from an infinite distant source. Welcome to the weird world of focused laser beams. Best wishes Russ

[@andyspoo2]

Great explanation. Your much appreciated by the laser community !

[@brunsniggel]

Have a 50W (china watts at least) 4060 Ruida System laser being shipped from Shenzen China as we speak! Thank you for this, great information. Keep it up :)

[@vkjnrokis]

there are plenty information about cleaning mirrors and focusing lenses. What about cleaning tube output beam lense? (Output coupler) how to do it? Would you do it?

[@fibranijevidra]

What an outstanding tests and anaysis!? :) Very fun to learn from you. You put a lot of work and effort into the creation of presentation of all these discoveries that we might take for granted. It amazes me that you do all the work yourself. Thanks a lot! Looking forward to another series.

[@uis194afm2]

Hi I think effort you put into the labs is excellent this has helped me tremendously and saved me time in my own projects.

[@eixenoeservices1937]

Hello Sir, Will the beam spot vary according to the power of laser? I would like to buy a 150W machine for engraving and cutting. Thank you!!

[@SarbarMultimedia]

Hi Eixeno The spot size is a so-called specification of the lens and not the beam. However After hundreds of test with different lenses and different laser beams (no, they are not all the same) I now know that the lenses are designed and specified as though they were going to be used in a telescope or camera to transmit images with NORMAL light. Our laser beam is nothing like "normal" light and lenses have their own different relationsip with laser beams that standard lens theory cannot deal with. The spot size you are interested in is the "burn" diameter you can create with a lens. A spot has no linear speed but you will make the burn diameter bigger by increasing the exposure time. Add speed and that dot becomes a line. That line thickness changes with speed. power and material being damaged. Power is great for faster and deeper cutting but to much power becomes uncontollable if you wish to do photo rplication where precision control of power is essential. A "jack of all trades" power is between 60 and 80 watts. It depends on your requirements . If it's mainly cutting that makes you money then go for the high power.. My advice is to stay away from Reci. SPT , Yongli or EFR are good choices Best wishes Russ

[@eixenoeservices1937]

@@SarbarMultimedia Thank you! Explained well. Hope I will travel with you along my laser cutting journey. Your videos are so information and technical about lasers. God bless you.💕

[@supaash82]

Hey Russ, have you found a robust solution when you are etching acrylic to avoid "ghosting" from when the acrylic is cut and the residue is blown back onto the surface of the material? Thanks, Ash

[@russsadler3471]

Hi Ashleigh. Acrylic is a fantastic material but it is not an easy material to work with. If you understand how it reacts to the laser beam you are part way to solving the problem you have encountered..You instinctively know what happens to a cup of water when you boil it hard. It converts from a small volume into steam which will completely fog out a room in a few minutes. In the same way there is a tremendous volumetric growth as you evaporate acrylic . If you take lower power cuts at high engraving speed you will cause the fumes to explode upwards. If you have the air management through you machine set up correctly then you have a fairly high velocity of CROSSFLOW air over your work That crossflow will carry those fumes backwards IF (and only if) you have a large gap between nozzle and work and also just a whisper of air assist to prevent lens fogging.. If you are impatient and try to cut with more power, you are instantly converting more solid acrylic into vapour. That vapour conversion rate is so high that it does not just explode upwards, it projects horizontally as well and will contaminate your work surface . Just experiment and observe very carefully and you will see the effects I describe.. Although there are several tricks to protect your unengraved work surface. It's the engraved surface contamination which is the real challenge.. Two or three light passes will be better than I deep pass. The clue in you question is "blown back down". Turn your air assist down to just a whisper toprevent the blowing down effect. Best wishes Russ

[@supaash82]

@@russsadler3471 thanks for your guidance Russ, as always 👍

[@BeeeeitchMrisker]

I am wondering what would happen if you fed nitrogen or argon into the air assist tube to prevent combustion on combustible materials. Maybe even flood the whole inside with Argon, it should hang around for a little while with the lid closed as it is a heavier than air gas. I wonder if you would be able to carve wood with more power without blackening. Possibly it would assist you with 3D carving.

[@SarbarMultimedia]

Hi William It's an interesting question to speculate on but I have no equipment or facilities to try either. One thing is certain, you will not destroy or reduce the energy transfer that takes place as the IR light stimulates the wood surface molecules into higher vibration states. The higher the vibration the higher the temperature of the wood. Even under an inert cover gas the wood is still going to heat up and some sort of chemical reaction will take place as the cellulose shakes itself to pieces. I am no chemist but I suspect there will still be some very local burning taking place within the cut because there is quite a lot of oxygen locked away in the sugar molecules. I am sure there are lots of guys out there with TIG weding sets that already have the argon shields gas that they could hook up to test your idea. Best wishes Russ

[@BeeeeitchMrisker]

@@SarbarMultimedia You have a good point on the side reactions. Charcoal is made by heating wood without the presence of oxygen after all. I'll have to try it when I get a laser in the next year or so!

[@zorwick]

So if I want to get good quality lenses for Chinese machine, where do I get them? (In EU)

[@russsadler3471]

Unlike tubes, where you can be ripped off with B grade reject tubes , lenses and mirrors are not as bad .There are lots of sellers on Amazon or Ebay but before you buy note the following. There are 3 baisc grades of lens if you buy ZnSe material. The colour is a good guide. If the colour is like honey or amber then these will be material of Chinese origin . If they look really brown , ignore them. but the honey coloured ones will be fine for power up to 80 watts and these are the cheapest and do a good job, If the lens looks sunflower yellow then this will be ZnSe material made by a different manufacturing process that originates in the USA. This material will easily run above 200 watts. The lenses will still be ground and manufactured in China but from US sourced material so the manufacturing quality ( the spherical geometry) will not be A1 but will be perfectly fine for our machines. They will not be the high precision geometry required for industrial machines......but then again those lenses will be X5 to X10 the price. There is a superior grade of lens usually made by a company called II-VI (two- six) that is the most expensive. In my opinion (having tested several) I see no performance gain from the premuim price. I will always recommend Cloudray as a proven and trusted source. If you are in a panic then go to the Cloudray shop on Amazon and there will usually be lenses stocked locally for next day delivery. However, if you go to the Cloudray website directly then the lenses will be cheaper and postage will be free, However, it will be about 3 weeks before they arrive. I always recommend holding a spare lens because this is the most vulnerable part of your machine. I hope this helps a bit Best wishes Russ

[@zorwick]

@@russsadler3471 Thank you! I ordered some from Cloudray Aliexpress!

[@phishinphree]

Would it help to mask off the outer portion of the unfocused beam at the tube or after the first mirror? It shouldn't effect the power of the central beam but wouldn't it cut down on the lower power shoulder region resulting in a sharper dot?

[@SarbarMultimedia]

Hi Even as I answer one question, this video throws up another. If only the central core of the beam is delivering the real power, where is all the rest going? I will in the near future try to isolate and measure the power in that central core. I tried occluding the outer portion of the beam with various sized sharp edged orifices during my search for the smallest dot. In that case the outer power seemed unnecessary. The orifices were very disruptive and did not aid my results. However, I do plan to use an orifice AFTER the lens to just let that central core of energy through to my dohicky. In that way I hope to determine what percentage of power finishes up in that central core.There is so much more to understand about the way lenses work for our technology. As I have discovered, this is a poorly researched subject. I am showing everything I do in detail so that others can experiment for themselves. This may be very simple shed science with very crude low tech methods but it gives us a pragmatic glimpse of how our lenses work. It does not tell us if there are quantum effects at play , that's the stuff for a well equipped laboratories and maybe the path to a Nobel prize for some one. Thanks for the comment Best wishes Russ

[@atrtsh]

I've tried this before, Russ has seen some of my results. The upshot is that a fast pulse from a focused beam, only lingers enough time for the tip of the curve to make a mark. Occlusion doesn't alter that, but does add other problems.

[@justplainlaser]

Hi Russ... Thanks again for another awesome video...

[@beardyandy]

Hi Russ, thanks for this series. I'm from a maker's group and have a kh7050b laser cutter, someone put me onto your series as they say you started with a similar one I'm largely going to start from the beginning of the series (maybe jump a couple) but as I've a bit to catch up on, I wanted to check whether there's any other helpful resources (website etc) you'd recommend please? Did yours come with air assist? Many thanks

[@SarbarMultimedia]

I don't want to be too alarmist but as soon as I see KH I know your machine was built in the KeHui factory. Mine was not KH , a bit smaller but probably similar to yours. Probably best to speak off line as I may need to see pictures of your machine. Add another comment with your email address and I'll contact you. I will also delete the comment from public view. Best wishes Russ

[@fbujold]

would you share the drawing for the slanted focus stand ? Please

[@SarbarMultimedia]

Hi Francois You are welcome to the drawings and I will also give more information. . Just add your disguised email address to another comment and I will reply and also delete your comment. You tube is becoming smarter at detecting email addresses and not delivering your comment. Be a bit smarter than their algorithms and disguise it in a sentence such as.....francois followed by a dot and then bujold. Use the normal and symbol; followed by gmail and then a dot and finally com. That approach has not yet failed. Best wishes Russ

[@shmulik152]

Hi Russ. Welcome back. A question not directly related to the subject of your video. In your experience, does running the laser at full power shortens the life of the tube more than lower power?

[@bobreichel]

I got a 1060 two days ago I'm using lightburn software but I'd like to try rdworks. I did download it but it only uses one file format and it's not one my other programs can save to. Wondering if you know where I can download a version that allows several file formats.

[@SarbarMultimedia]

What program are you trying to use with RDWorksand what file formats have you tied. You cannot LOAD external files, they all have to be IMPORTED. Best wishes Russ

[@bobreichel]

@@SarbarMultimedia Drats it's my fault. I was doing open and not import on rdworks. Sorry for bothering you about nothing.

[@brunocarvalho4239]

Video incrivel! não entendo inglês, mas só em observar todos os parâmetros que você usou para justificar e explicar como funciona o foco das lentes da máquina a laser consegui entender!.

[@SarbarMultimedia]

hola bruno Presione el botón CC en la parte inferior de la pantalla para activar los subtítulos en inglés. Ahora presione el botón AJUSTES y seleccione SUBTÍTULOS. Tendrás la opción de elegir el idioma de los subtítulos. Eso te hará la vida más fácil. Esto es solo parte de mi largo viaje para descubrir cómo funcionan realmente las lentes y los rayos láser. Tengo una máquina de RF de 30 vatios con un haz de diámetro muy pequeño y soñé que el perfil de alta intensidad de este haz sería fantástico para cortar después de pasarlo a través de una lente. Lamentablemente, no fue porque la lente no enfocaba el haz de la manera que esperaba. ver kzbin.info/www/bejne/m3-VmXWkga-Vla8 Luego pasé a descubrir finalmente cómo el perfil de intensidad de un rayo láser se distorsiona lejos de un perfil de intensidad gaussiana ANTES de que llegue a la lente y luego cómo este "haz parcial" daña el material después del punto focal. ver kzbin.info/www/bejne/oZXHhHmFYs55hK8 gracias por las palabras amables Los mejores deseos ruso

[@CloudrayLaser]

Great Work.

[@startinsomethin]

Would be interesting to know how much of a role PSU overshoot plays

[@uis194afm2]

new to this some of your items like the laser alignment are interesting do you publish the DWG dxf anywhere .

[@SarbarMultimedia]

Most of my files are available for download on www.rdworkslab.com. But if you have difficulty then add your email to a comment with what you want and I will reply and also delete your email/comment from public view. Best wishes Russ

[@Lesept00]

I haven't gone through the series yet, but maybe for thick materials the focal point should be _inside_ the object, possibly half way the thickness.

[@SarbarMultimedia]

I am in the privileged position of being retired and with no commercial pressure to use my machine as money maker. I also have the luxury of support from Cloudray who want to know the sort of details about lenses that you are enquiring about. If you watch this video kzbin.info/www/bejne/r4CVhXeVnZ2SpKs You will see that have LOTS of different lens types , some are not commercially available but were obtained for me . I test them in different orientations, focal positions and on 3 completely different materials so that i do NOT generalise my conclusion on the basis of just 2 or 3 lenses which is the maximum that most users would ever experience. I confront several myths with the data I obtained. one of them being the myth that you start of with. Best wishes Russ

[@mikesfarmmikesfarm3977]

is it true on the east coast of central florida i can not just run a chiller and use a 100watt co2 laser similar to yours in my garage ? I REALLY want to get a chinese laser. regards mike

[@SarbarMultimedia]

Hi Mike I know that in your part of the world it can be high 30sC and VERY humid in the summer months. I see no reason why that will stop you but there are just two considerations when buying a machine. First is to buy a tube with good insulation and protection around the high voltage end of the laser tube. There could be 35Kv in that area and unless it is well sealed then your humid atmosphere may give a low resistance path for arcing (lightning) between tube and case. This just a possible issue. A certain issue will be cooling. Depending on the tube manufacturer there are varying allowed operating temperatures. Cheaper tubes say 25C max and the more expensive tubes allow up to 40C. I have operated my machine from 5c to 45C with no major issues other than about 5% loss of power above 40C. I try to stay below 30 C most of the time. That is pretty easy in the UK without any special cooling measures.. In general most folks in your climate zone use an industrial Chinese chiller CW5000 but at $450 that''s a big punishment for living in a warm climate. There are much cheaper DIY ways of cooling that don't involve the high power requirements of instant cold. It depends on what use /how much use you envisage for your machine. So as you see , there are minor difficulties but nothing to prevent you having a machine . I am speaking to people all round the globe with these machines including Brazil , Africa Arabia , India and Pakistan. All are running with no major issues. Best wishes Russ

[@prashantsharma8958]

hi sir... I have china laser cutting with MPC 6585 Leetro controller. Having issue with IMAGE engraving. Machine not accepting new image file. it work only an old image stored in controller. can work with new vector file but cant work with new image file. Any help???

[@SarbarMultimedia]

Hi I seem to remember that your controller uses LaserCut software. I am afraid my knowledge of both software and controller is zero. However as a logical problem it seems that something has gone wrong with the LaserCut encoding. If some file types work OK then there cannot be a problem with data transfer. The first thing I would try is to reinstall the LaserCut software, upgrading if there is a later version. I am sorry that I cannot be of more help. Best wishes Russ

[@prashantmadavi]

I have 100w co2 laser machine. I replaced laser tube before 2 days I set all in correct way. But there is some issues when I give pulse spot it gave two spots . I tried on 2 mm MDF so that time machine is cutting job but at the time two cutting line running on job simultaneously. Please help me . I need your email I’d I will send my machines issues please reply photos and video

[@SarbarMultimedia]

Hi Prashant Sadly I don't make my email address public but if you wish to add your disguised email address ( (prashdotmadatyahoodotcom for example) then I will reply to you and also delete your comment/email address from public view. Best wishes Russ ps It sounds like your beam is nor passing down through the AXIS of your lens tube If you remove the lens and cut a card disc the same size as the end of your lens tube, attach it centrally with masking tape and put a pulse mark on the disc . Remove it carefully and I guarantee the scorch mark will not be in the centre.

[@prashantmadavi]

Sir you have any video please share it on [e-mail]

[@prashantmadavi]

Thanks for your reply sir

[@javierzapanacaceres2933]

So how when put the lens what is the correct way to ??

[@SarbarMultimedia]

Hi Javier There is no correct way . It depends on what you wish to do. For cutting the best way is flat side down but the focal distance may be 1mm less than the setting piece the Chinese supply. When your machine arrives you will always find the lens fitted with flat side up . This way round produces a smaller burn spot which is better for engraving. Most people don't bother with flipping the lens but keep it flat side down. Unless you are trying to do precision photo engraving flat side down produces good all round performance. Best wishes Russ

[@javierzapanacaceres2933]

@@SarbarMultimedia wow that's very very interesting, thank you so much for the useful information. I'll make some test Regards

[@steveh8724]

I've been watching several of your videos with great interest! I have no direct experience with CNC Lasers, though I do have a CNC mill and I did take physics in college. Anyway, I see what you're getting at with your interesting ramp experiments, but I do have a problem with references to 'dynamic focusing'. I think we should separate the optics and optical definitions vs. the cutting effects. So, no, the focal length and the instantaneous focus of the laser energy *does not change* as the speed of the laser head movement over the substrate changes. What is happening reflects the complex interaction of focus (fixed effect) vs. rate of local energy delivery per unit length of travel of the beam over the substrate. Consider the following 2 edge case scenarios all executed with the same (ideal?) focus of the laser cutting, say 5 mm cast acrylic: 1) 'Slow burn case': In this case, the laser is moved ridiculously slowly along the cutting path and one gets an extremely wide and ugly 'cutting' line 2) 'No burn case': In this case at the opposite extreme, the laser is moved so quickly that the laser has no discernible effect along the cutting path. Obviously the region of practical utility lies between these two extremes. While all else is held constant, imagine runs starting with scenario 2, but with slower and slower cutting head movements. As travel along the cutting path slows, you see first the faintest beginning of etching and these will reflect the smallest 'static' dot size if that is how the laser was originally focused. As speed is further decreased, depth of cut and width of cut will increase. For practical cutting, you have to set the focal point below the surface and set the speed and laser power such that a clean sharp cut is achieved. There is no 'dynamic' focus. But the dynamics of the cutting situation will affect the where the ideal focus depth is for a given substrate (material & thickness). Sorry to ramble on, this is really interesting stuff. Hope to have a CNC laser to work with soon and look forward to more interesting videos from you!

[@SarbarMultimedia]

Hi Steve In several of my sessions I have clearly demonstrated the effect you describe where the speed effect (energy deposited per unit of time) causes the the damage track of the beam to get thinner with speed. I entirely agree that this effect cannot be anything to do with the focus because I can show this effect with no lens in place. No, the apparent change of focus I am observing is caused by the Gaussian energy distribution within the beam. My brain works in a very naive way and I like to imagine equivalent real world pictures to lock in these flimsy concepts. In this case i imagine a very thin pointed artists brush. The brush may have a body thickness of 2mm but the tip of the brush will be almost zero. The lighter the application of pressure, the thinner the dots or lines the brush will make on the canvass. I do understand that the focus point of a lens is a fixed property. However just because the beam is focused with a lens, it does not lose its Gaussian energy distribution. It is this complex relationship between the focal point and the non-uniform distribution of energy within that focused beam that is responsible for this apparent variation of the focus point. That paintbrush I imagined is still there at the focus point but it is the BODY of the paintbrush that exists at the focal point , the tip is below the focal point and it is this VERY high energy tip that is doing material damage below the focal point. I am neither an optical engineer or a physicist but I suspect lens features are defined and tested with pure uniform monochromatic light sources. We are not using such a light source thus the practical world results I am discovering are somewhat different to the the lens theories I have always believed in. You must always remember that these videos are a look over the shoulder of an old guy on a journey of discovery. I see something that does not make sense and then try to use simple shed science to tease the truth out of what I am seeing. I may draw an incorrect conclusion from my experiments and observations (and I have done so several times on this journey) but you can see those same tests and if there is an alternative explanation that may get to that truth quicker, then I am only too pleased to slot your piece of the jigsaw into the big picture I am building of this technology. I greatly appreciate your comment and feel sure that you will come across some things that do not make sense when you get your own machine. It is a fascinating subject and of all the parts I have explored , lenses (the final and most vital part of this machine) seem to be the lest understood. Best wishes Russ

[@bobreichel]

I've been watching your videos. Extremely in formative. I was wondering if the 1st mirror that the CO2 laser tube hits, If that mirror was slightly concaved and the laser was aimed dead on center would that make the beam more focused and stronger as an end result?

[@SarbarMultimedia]

Hi A laser beam is a coherent beam that, for the short distances within our machines , remains completely parallel. A concave mirror 1, will make the beam converge to a focus point somewhere. Where should that point be? Just consider the variation of the beam path between the back left corner of your table (maybe 200mm long) and the front right corner of your table (maybe 1800mm long ). A parallel beam will serve both situations equally a converging beam will not. Best wishes Russ

[@SarbarMultimedia]

Hi I note you asked a question about swapping from a constant current tube to an RF tube. Sadly when I went to answer, You Tube had teleported it to a parallel universe I'll answer here in the hope that you may get notified of my answer. I cannot answer you question from any direct experience. I think you will need two power supplies and a very expensive tube. RDWorks caters for RF tubes in iyt's vendor settings and once the beam exits the tube it is no different to the standard beam except it is not constant but in varying high frequency pulses. Technically this should allow high precision power per dot control for photo engraving but I have yet to see any evidence of this because the people that use these tubes (the "big boys") do not use dithered dot engraving but rely on half tone (newsprint) engraving. This technique relies on creating different size dots which is puzzling to me because we can only do fixed size dots. I would never upgrade to RF thoug because for for 1/20 of the price I can achieve excellent engraving results. That is the whole point of my channel , learning to extract the absolute max from a very cheap machine. I accept that an RF tube may do it quicker, provided I upgraded the rails, the belts ,the motors and the drivers to allow me to run at over 1000mm/s instead of my existing 500mm/s . So what is the real point. The only time you would see a benefit is for engraving. When it comes to cuttiny you are down in the 5 to 30mm/s range and you need raw power. There is little difference in cutting performance. I know of a guy here in the UK that make a comfortable living with his tech support business swapping out RF systems on machines to reduce running and replacements costs. I am very happy with what I have and there is still much more for me yet to learn. Thanks for the comment and I'll be happy to receive your impression of advantages if you do decide to spend your time and money Best wishes Russ

[@bobreichel]

@@SarbarMultimedia That's because I took it off as i meant to say a ceramic laser tube.

[@RoadstarRider1]

Hey Russ !! I'm anxious to start soaking up some of the knowledge / experience you have to offer, I think it makes sense to start from the beginning. I'm pretty new to Laser work having only a few months of engraving with a 4.2w Diode ... How to I find the beginning of your videos so I don't miss the basics? Thanks for your work, Tim

[@SarbarMultimedia]

Hi Tim You need to be very careful when you read my stuff because it is based on two basic things that you will not have. One is RDWorks software that talks to a Ruida digital controller and second a CO2 laser. The CO2 laser works with invisible IR light at a wavelength of 10,600nm whereas your blue diode works at about 450nm in the visible spectrum. I urge you to do reading elsewhere because light is a funny thing and different materials are stimulated in different ways by the different frequecies of light. Things that absorb or reflect light at 10,600nm may react completely opposite at 450nm. Just a few mw of blue laser light will damage your retina and cause permanent blindness so be ultra careful and do a lot of specific reading about your type of laser. Sorry I cannot be more helpful, Check in again when you decide to move up a notch or two. Best wishes Russ

[@bobreichel]

OK here's a question why can't they make a laser tube refillable. So if the gasses are no longer stable you could just refill the tube.

[@SarbarMultimedia]

Hi I answered your previous question in an old comment of two weeks ago because you last comment has disappeared Some tubes are refillable but they are the expensive top grade industrial tubes see www.parallax-tech.com/ for an example. However the cost of filling a tube is only marginally less than buying a new tube and that's at least 10 times more that I paid for my whole machine. These tube have a long warranty (3 or 4 years) but my £300 60 watt tube is already 3.5 yeas old and still running like new. Industrial users have to have a different mentality towards equipment and spares .Maintaining production is paramount so the high cost of something with a guaranteed performance is just part of the cost of running a process. I know this because I was there for 10 years running expensive metal cutting machines.. Best wishes Russ

[@bobreichel]

@@SarbarMultimedia Ok, well done. That was good information, thanks.

[@copingerlightrailway9573]

Hi Russ. Can you still supply Dohickys? Great series of videos. Thanks Adrian

[@SarbarMultimedia]

Hi Adrian. Sadly You Tube canned their private message system a few months back. so now all you can do is to add a separate comment with your email address. I get auto copied to my gmail and will answer but at the same time will delete your comment/email from public view. Best wishes Russ

[@bonplan92]

thanks you so much for explaind , is a gold in bar for me .

[@josephlovell6951]

Absolutely brilliant

[@SarbarMultimedia]

Hi Joseph How lenses and laser beams interact has taken me a long time to understand. Thus my knowledge of lenses from 5 years ago has changed a bit. You may like to update by looking at these videos kzbin.info/www/bejne/bX-bhZtnYq55atU and kzbin.info/www/bejne/rGiQh3Sof8d9itU

[@josephlovell6951]

@SarbarMultimedia I have watched many of your videos over the last week. I love how you keep digging into them . Although sometimes your concerns are not clear. But I get it you need more data before you can make that leep. I did subscribe so I can stay up to date. I just got an older co2 laser 50w that I have updated to 70w tube and power supply. But looks like the controller is very old so I need to learn RDWorks

[@SarbarMultimedia]

@@josephlovell6951 Hi Joseph Always bear in mind that these videos are not rehearsed and that you are looking over my shoulder as I experiment and discover. This is a record of a learning journey and as such some sessions will be very much "follow your nose". It may take many sessions to arrrive at a sensible conclusion. It took me about 3 yeas to discover exactly how lenses managed to focus the beam to produce a deep parallel cut. There is no need to learn RDWorks if you are used to using Lightburn. Lightburn was created 7 or 8 years ago because a very capable software programmer who was also a laser hobbyist, became aware of the limited capability of RDWorks and it's very clunky interface. He set about reverse engineering RDWorks to create Lightburn. So with just a few exceptions, everything in Lightburn is in RDWorks but the usability and features of Lightburn are from a different planet.. Lightburn has now been developed into an industry standard package where it can be used with any type of laser or laser controller using Linux. OS or Windows. RDWorks is still Widows only.

[@josephlovell6951]

@SarbarMultimedia thanks for the information I have a morn 3050. It has a RDL8082 B main board. That I can find any thing on it. So unless I can contact to it. Witch I have not tried at this time. Because I fear I won't have the driver's for it. So I will cross that bridge when I get there. I have parts on order to fix the cooling system. Just trying to get as much knowledge as I can for now. I'm hoping I can make it work and not have to spend 400 for a new contractor. Still think your work is brilliant. I bit surprised at some of the rezol

[@SarbarMultimedia]

@@josephlovell6951 Hi Joseph I think your machine will be fitted with a RDC6442 controller see www.google.com/search?q=RDC6442&oq=RDC6442&gs_lcrp=EgZjaHJvbWUyBggAEEUYOTIGCAEQRRhB0gEINTEzNGowajeoAgCwAgA&sourceid=chrome&ie=UTF-8 If so then either Lightburn or RDWorks will be OK and there is no need to upgrade.

[@beko_byanko]

Hello, how can I contact you regarding a problem with my machine, with your permission?

[@SarbarMultimedia]

Sadly KZbin will not publish emails . However you can contact me privately with this contact form forms.zohopublic.eu/ndeavorlimited/form/K40XtreeemLaserCutterContactRussSadler/formperma/k2Cn0QN5ChpazfTMAUw25lZ-FKpjZa96TQWHjv3ntOg Best wishes Russ

[@MrArrow1961]

Dear Russ, thx, for very good video's and question here, in this one. I think it is material ph. density that cause such diff. Acrylic polymer can not be produced at 100% same ph.density at its thickness. Sincerely hello from Armenia

[@BuiltNotBoughtUK]

Very interesting video! Will have to design a jig at some point to do similar tests. Very very cool! Thanks!

[@richardm1205]

I have a 50 watt Chinees laser and I don't know how to transfer any drawings or other stuff from CorelDraw 18 to R&D works? and do you know how to weld fonts in R&D Works? Thank you and I enjoy your videos

[@SarbarMultimedia]

I have the very latest issue 38 of RDWorks and dealing with overlapping shapes is just not available. Can I sugget you install a free 30 day trial of Lightburn , a privately developed version of RDWorks with MANY more features. It auto deletes the overlaps in script fonts and imports many more file types.although not .cdr files. but you can always save as a common file type say bmp for pictures and use .ai or .dxf for vector files. see lightburnsoftware.com Best wishes Russ

[@bobreichel]

Another question which is better Copper or Molybdenum mirrors

[@SarbarMultimedia]

Hi Copper is better BUT you cannot buy them raw, they will be gold plated so they are not copper......and they are expensive. I have had 98 to 99% efficiency from those I made but it cost me a lot of £s and time to prove this whereas Moly mirrors are 97% and cheap. Go for moly every time don't touch anything that is plated. Silicone mirrors are expensive and must be flash gold plated because silicone is not a reflector whereas gold is. Best wishes Russ

[@bobreichel]

@@SarbarMultimedia Ok thanks. I bought a 1" round copper bar to make and polish my own. I'm also going to try electropolishing and see how well it will polish the face.

[@SarbarMultimedia]

@@bobreichel Hi Polishing is easy but flatness is not. As I discovered it takes very little imperfection to cause beam divergence and that happening 3 times causes beam shape and power issues Good luck with your challenge. Best wishes Russ

[@bobreichel]

@@SarbarMultimedia I'm going to polish the surface while on the lathe which should be a lot easier to keep it flat.

[@bobreichel]

I was looking at fiber laser engravers and I notice that a 50W fiber laser engraver can engrave on metal yet a 100W CO2 laser cannot. I was just wondering why is fiber laser so much more efficient or powerful in engraving Then a co2 laser? P.s. And on a lighter note my favorite beer is Newcastle Brown ale.

[@SarbarMultimedia]

What you are observing is one of the interesting properties of the electromagnetic spectrum. Our eyes are tuned to respond to a VERY small range in the middle that spectrum see opentextbc.ca/introductorychemistry/wp-content/uploads/sites/17/2014/01/899f109376d5dfc6ee9209e950ded122.jpg Other materials can be excited by specific wavelengths in that spectrum. The example you note is at a wavelength of 1060 nanometers which is just above our seeing range and is called near infrared ie a wavelength of 1.06 microns. The CO2 laser emits light at 10x longer wavelength ie 10.6 microns and excites the molecules in materials in a different way. Imagine every material to be a different length childs swing ( a pendulum). If you push the swing at the correct frequency you can keep the motion going. Chose the wrong time to push and you will kill the motion. So for every material there will be a right and a wrong wavelength that will or will not excite the molecules. The more excited the molecules the hotter their temperature. The phenomenon you mention about the inability to engrave metal with a CO2 laser is because ALL metals act like mirrors to 10.6 micron wavelength light. if the light energy is reflected (some reflect better than others) then the light energy cannot excite the molecules and raise their temperature. This reflective property is all to do with the crystallography of metals However, IF you can change the metal from solid to liquid then it will become sensitive to excitement at 10.6 microns and will heat up rapidly. It is possible to engrave THIN naked stainless steel ( which is 96% reflective) because 4% of a highly focused beam is enough energy to stimulate melting before the mass of background material conducts the heat away. Yes it is possible BUT it is very dangerous for your lens because it means that 96% of the energy is reflecting onto the face of your lens and will very quickly remove the anti reflective coating. You will see me doing this experiment in kzbin.info/www/bejne/oIGcn5aNoNh4fdk. I subsequently discovered the damage to my lens. As I say in the video, I understood there was a risk but, hey, you needed to see what was possible even though it was foolhardy. Best wishes Russ

[@usmankhanshano8161]

Sir i have 130w reci laser machine.. & i want to cut MDF in fine quality.. which lense is best ?

[@SarbarMultimedia]

Hi Usman The lens in only part of the solution, the correct nozzle, air assist and good airflow UNDER your work are also essential elements for a nice clean cut free of smoke damage top and bottom. With 130 watts you could use a 63.5" focal length lens, it depends on what thickness MDF you plan to cut. For anything up to 8mm thick I would recommend a gallium arsenide plano convex lens used flat side down. I am in the middle of a big lens testing exercise at present and I have not reached a definite conclusion but for the past 3 years I have been using this lens as the best go to lens for cutting with my 60 watt tube.. NOTE. if you have a through the lens red dot pointer then this lens does not transmit visible light so your red dot will not show. If this is a problem and you need the pointer you will have to revert back to a zinc selenide lens with the same specification. see www.cloudraylaser.com/products/cloudray-gaas-focus-lens-dia-19-05-20mm-fl-50-8-63-5-101-6mm-1-5-4?variant=44518202184 or www.cloudraylaser.com/products/china-pvd-znse-focusing-lens-for-co2-laser?variant=43422450056 Your nozzle needs to have a small orifice (2mm to 2.5mm) and sit between 3 and 5mm above your work surface. You do not need high pressure air assist, the little pump they normally supply delivers about 4psi (0.3bar) which is perfect for the job. You have to keep you nozzle small and close to the work to make sure that you get an EFFICIENT flow of air passing through your cut to push the fumes out of the BOTTOM of your cut. Fumes coming upwards will get blown back onto the surface of your work and make it brown. It is equally important that once those fumes have exited the bottom of your cut , they get drawn away very quickly. Sitting your work on a honeycomb table will NOT give you that flow as it is a series of closed cells. Make sure you raise youe work off the table by at least 15mm so that you get good airflow BENEATH your work.. Finally, look carefully at your machine design for air management issues. Many machines have little of no open area (grills) at the front cover to allow air IN. You cannot get air flow with extraction only, You must have an open area that is typically twice the area of your extract duct. The best and most effective way to achieve this will be to use 30mm or 40mm spacers at the bottom of your door frame to prevent the door from closing. This will allow a curtain of air to freely enter the front of your machine. Best wishes Russ

[@usmankhanshano8161]

@@SarbarMultimedia sir MDF thickness is 2.5mm TO 4mm..

[@usmankhanshano8161]

I need clean cutting free of smoke..

[@SarbarMultimedia]

@@usmankhanshano8161 Hi Usman It depends on the size and complexity of your detailed cuts but in general you need to set the power to maximum (65 to 70%??), and find out what maximum speed you can run at. The faster you can run the cleaner your edge will be BUT all the points I made previously are essential for a clean cut. With these guide lines you can experiment and find out for yourself. . You should be able to cut 4mm at 20mm/s or even faster. If you can get low level formaldehyde MDF it will be much lighter in colour and less liable to edge charring.. The fumes are also less dense. see onetouchlaser.com/products/99109--laser-grade-mdf.aspx Best wishes Russ

[@cicciofranco405]

Congratulations from Palermo, I'd like to buy a book in Italian of everything I've seen in your films ... is it possible?Francesco pa.

[@polakis1975]

Let the adventure begin!

[@marouaneladjel1907]

I am very happy to see you

[@mijaresaldo]

Great video. Thank you.

[@diegoseminariodecol3863]

Amazing work my friend

[@SarbarMultimedia]

Hi Diego. This video is now two and a half years old . About 6 months before this video, I became aware, as I was testing the cutting ability of various lenses, that there were some serious flaws in the "facts" that we were being taught about lenses. On and off, I have been wrestling with the problem of trying to understand how lenses and laser beams work together. I could see from my many experiments that lens theory could not explain any of the behaviour I could easily demonstrate. In recent videos ,I am now at #217 I have finally decoded how lenses and laser beams work together and although no laws of physics are being broken or bent, the idea that lens theory can be read across to lasers is totally incorrect. Lenses and laser beams have their own secret relationship that it seems no one else has ever bothered to investigate. There is nothing wrong with lens theory and in fact lenses have to be designed for the predictability of uniform intensity light rays as used in any IMAGING system such as a camera, telescope, microscope, projector etc etc. A laser machine is NOT trying to project an image so the rules rapidly break down. It's taken 3 years of piecing together many simple positive and negative experiments to finally uncover the full picture. You have lots of video to watch!!! Best wishes Russ

[@diegoseminariodecol3863]

@@SarbarMultimedia thanks for the reply Russ, I just start working with my laser machine and found your videos that are in another league ! Thanks for sharing all your work and experimentation. I really hope that there is more people like you out there that lives by the "I dont belive anything that anybody told me, I have to prove it from myself" mindset. Its very confortable to see someone digging in the science part of the functionality of this machines, and of course I will pass these days watching all your content haha. Greetings from Perú and sorry for my english that I just barely write. Diego

[@SarbarMultimedia]

@@diegoseminariodecol3863 Hi Diego Never apologize about your language proficiency. We only need to make ourselves understood and that does not require perfect grammer. Your English is 100 times better than my Spanish!!!! If it's more comfortable , write in Spanish and I can use Google translate. Best wishes Russ

[@willswings]

when it comes to knowledge, I know 'i'll find what I want in your channel . very instructive! you're the Laser Doc ;-) for your final questions about focus in the acrylic, maybe you'll find the answer on a different place that you have search for. Maybe you can Look more at the photography knowledge. I'm a wild photographer enthusiast and it seems to me that I've read something that is close to explain this in the hyperfocal theory.

[@SarbarMultimedia]

Many years ago I was a keen photographer also but jumped ship for 8mm cine film. I have stayed with moving pictures ever since. Add this experience to my college science and I have a moderate understanding of light and lens theory.. I was sure that lens theory was absolute and would allow me to understand how out laser technology worked. It took 2 or3 years for me to realize that some things were just not making logical sense Every lens focal length has its own theoretical spot size through which all the light rays pass. The longer the focal length the bigger the spot size. I encountered several articles discussing energy density and obviously squeezing the same 100 watts (say) into a smaller spot size creates a higher energy density and the potential to do more damage. As an example if we regard the energy density of a 1.5" lens to be 1 then a 2" lens energy density is about 0.5. Ie the larger spot size appears to be less powerful. . I realized that there was a paradox when my cutting tests showed the 2" lens had more cutting capability than the 1.5" lens and a 2.5" lens even more so. Also why could I cut 10mm thick material with an almost parallel sided cut using a lens that rapidly loses its energy density after its focal point. I hunted for research papers on both these topics and drew a total blank. Thus with only imagination and very basic equipment I have tried to decode what is actually happening. during cutting to explain these apparently illogical results. My latest video about focus begins to illustrate some interesting properties of lenses that I think will eventually lead me to significant increases in cutting power without upgrading the laser tube. see kzbin.info/www/bejne/i2WqhXyHrK2ogJo Best wishes Russ

[@willswings]

@@SarbarMultimedia big thanks for the time you've taken to answer me. I'll check this vid asap to see what you've discovered. always a pleasure. btw, I wish you merry xmas. Best regards from France.

[@prashantmadavi]

Sir I need some help

[@luigibasa95]

@sarbarmultimedia Fantastic video! I was thinking... why don't you write articles about your work? You should at least write a book! I surely would buy it!!! think about it!

[@SarbarMultimedia]

I am gradually building a separate and succinct series of videos on various important topics and I plan to make a double BluRay disc. Howver, so many things for a retired guy to do and still so much to learn about this technology beyond the basics that most people survive with. But don't hold your breath. Best wishes Russ

[@gordon8065]

would you video cutting smoke

[@SarbarMultimedia]

Hi Smoke is only visible because it is micro solid/liquid particles suspended in air (example = fog) Those micro particles will be excited by the IR light energy and heat up. In the case of what you call smoke, they will usually contain hydrocarbon particles that will heat up, give off flammable fumes and spontaneously ignite . That ignition triggers heating of adjacent particles and all of a sudden you have a bonfire. So the closest I can get to your request is this. kzbin.info/www/bejne/mmbJdXl_j62jfNU Best wishes Russ

[@arpanchoudhury_]

thank you sir again

[@eagleeye5520]

I salute you man

[@thebeststooge]

WOOHOO

[@SpottedDogDesigns]

Its all Quantum Physics LMAO