RDWorks Learning Lab 39 Understanding Lenses
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- čas přidán 14. 01. 2016
- If you own a Chinese laser cutter this little series of videos about me learning how to use the free software provided, may solve the problem of trying to learn from a virtually unreadable manual.
I am nothing to do with RD Works, I am not an instructor and I am no expert. This series will document the essential bits of many hours of trial and error - Věda a technologie
"Bigger isn't necessarily better, and you can do quite a lot with a short one!".....Brilliant!
I'm dying here, so good!
Perfect ending sentence...
Wow... turned my power down from 85% to 65% and now cutting much better, much deeper and most important for me much faster , Fantastic series of videos, thanks for your dedication
And presumably your using less electricity in the process :-)
One point you missed about air assist...It blows out the fire when, things catch on fire. I'm glad you caught on to both keeping the smoke off the lens and blowing the crap out the cut. I will be working on a modification to add a little air ABOVE THE LENS, because it is completely open to the smoke in the cabinet and seems to be
the number one collection point for a dirty lens.
Hi Dan
Remember this video was done 5 years ago when I was just at the beginning of my learning journey with this technology and was beginning to discover the importance of various aspects of the machine. There turns out to be a lot more to air assist than the basic understanding that most people have. I began to realize that a significant part of laser cutting /engraving is understanding what the laser beam is (yes, just a beam of invisible light) and how that light energy gets converted to molecular vibration at the surface where it contacts. The level of molecular vibration= temperature (it's worth Googling to understand this). As the molecules vibrate faster they shake themselves apart and form new chemicals. It is those new chemicals (smoke and fumes) that you are reheating with the laser beam and undergo further chemical change and catch fire.. If you can blow those fumes away from the path of the laser beam (out the BOTTOM of the cut) then there will be nothing to ignite. This is not quite true in the case of acrylic so you may like to watch this short video czcams.com/video/eaz9ZEjwjfs/video.html
As the video begins , stop it and look at my lens tube. It is very short and VERY open at the top. I have 3 machines like this and in 6 years I have never experienced debris on the top surface of my lenses. I can only assume that your cabinet becomes smoke filled during cutting? Air flow management is the secret.....don't let the smoke anywhere near the top of your lens tube. Study your machine carefully because I'm sure that additional above-lens purging is not fixing the real problem.. This video (from 42:30) may give you some understanding of the importance of air flow management. czcams.com/video/AHnJ2WxNo5Q/video.html
Best wishes
Russ
That last sentence earned you a thumbs up.
Great video again! I can benefit so much of your work, thanks a lot!
Another very useful video indeed. Makes lots of sense, hence I ordered a 38.1 mm lens. Thanks Russ.
Thanks for all the effort you put into these tests. Very interesting.
+Bruce Fleury
Hi Bruce ,
I'm just selfishly enjoying myself digging into areas the interest me. If it interests you too, then that's a real bonus. Thanks for your appreciation
Russ
+SarbarMultimedia
Russ,
I, too, want to add my thanks. I ordered a 18mm FL38.1 lens for my machine ($31 US). When I took the lens out to measure its diameter, I found the original lens was installed flat side up, just like yours. Thanks for saving me that headache! I also saw they have an FL25.4 lens with a shorter air nozzle head, but I'm not that brave (yet).
Thank you so much, fascinating about the air assist, the tests you have done and comparison of the actual power density.
As my k40 that I am heavily modifying does not have that much power I will look to use a 38mm lens like you - however I realise how incredible accurate the bed height needs to be. Currently I just eve it ad stack some crap wood underneath.. Now i'll be getting exact sizes and making everything absolutely perfect.
Thank you so very much sir.
Am really enjoying your videos, I have the cheaper K40 (40watt) laser which I've modded by adding a pointer, air assist and modifying the fume extract. Your vids highly informative. Jealous about having retirement to fool around with the kit though.......hopefully not too many years to go though!
+IanScottJohnston
Dont wish for it. I'm sure the wife will already be "planning" your retirement activities........it's not all playing with the machine!!
Thanks for your appreciation
Russ
Great video for us just stepping into this arena. Simple, to the point and bulging with usable information!
Hi Greg
In general these facts are right......but it turns out , not for our laser cutting or engraving. I have mapped the energy density profiles of many lenses and those results clearly demonstrated that the commercial lenses that we buy for our machines do not perform anywhere near what I was passing on in this early video. As my learning journey progressed I was finding more and more things about the performance of lenses that didn't make sense. I have looked at the performance of lenses for photo engraving and also for cutting but none of the experimental work has given me concrete answers about what is actually happening I started a new investigation just recently that I hope will finally answer some of the many questions that nobody seems to have absolute proven answers for. see
czcams.com/video/MU5uT2XnuWU/video.html
czcams.com/video/zJjAr-TANQk/video.html
czcams.com/video/YV_BZ1US7vY/video.html
I am still doing the cutting tests and sxpect to issue my results in the next week or two.
Best wishes
Russ
I have been trying to produce plastic kit buildings for railway modellers but could never get my parts as 'crisp' as some of the laser cut kits advertised in the model magazines.
After watching this video and switching to a 38mm meniscus lens I have 'cracked it' and my cuts are the equal of the commercial kit makers.
What a valuable resource RDWorks is.
Keep up the good work.
Hi I am glad you are seeing great improvements. Bear in mind my series is a learning journey and at this point I did not understand the importance of air assist to good clean cutting. The chances are that by using a shorter focal length lens your nozzle is now much closer to the work. Getting your air assist directed efficiently INTO your cut will be the main reason for your improved cutting. That is something you will come to understand about later in the series.
Best wishes
Russ
@@SarbarMultimedia I am already looking in to improving my air assist, I upgraded my airbrush compressor and the old one is about to replace my existing air assist compressor. It is a tank compressor with a pressure regulator so I will have smooth air delivery. I have improved the air valve on the nozzle to improve flow.
@@captainswoop8722
Be a bit careful about using even regulated air from a shop compressor. Because the pressure starts off very high, the temperature of the air in your reservoir is hot and absorbing water they has condensed there. When your air drops its pressure (usually as it enters your nozzle) the rapidly expanding air cools and releases its water as micro droplets. The laser beam will heat those droplet and they will rise to the face of your lens. Gradually over a short time you will find a film being baked onto your lens. I destroyed 2 lenses when I swapped to my tank compressor. After 3 weeks I was back to the little pulsing pump supplied and because it works at 4 or 5 psi there is no such risk because the air never heats up and there is no reservoir. Never had a repeat of this problem since the change back. I warn you so you can keep an eye on your lens.
Best wishes
Russ
@@SarbarMultimedia Thanks for the warning, this isn't a 'shop' compressor, it's an airbrush compressor, it has a very good moisture trap, runs cool and can be regulated down to just a few psi and low volume.
I was thinking of rigging it as seperate air supply directed at the plastic face to keep it cool and stop the edges of the cut and corners going 'soft'. I am mainly cutting thin modified acrylic 'rowmark' plastic between .75 and 1.5 mm or engraving detail in to the surface.
@@captainswoop8722
There is always a dilemma when it comes to cutting and engraving on one job. especially multi layer plastic as you are doing. For sfficient cutting you really need a small nozzle (2 to 2.5mm diameter) and a 3 or 4 psi air assist to blow the cut debris out of the BOTTOM of your cut. To achieve a focused air flow through your cut your nozzle needs to be close to the work (3 to 5mm) You do not want ANY smoke/fumes coming upwards or they will immediately get blown back onto your work. Engraving requires exactly the opposite conditions. The nozzle should be 4 to 6mm diameter (no jetting effect) The air assist should be just a whisper to keep a positive air pressure in the nozzle to protect the lens from fogging. The gap between work and nozzle should be as large as possible (anything from 12mm upwards).
Let's stop for a moment and consider a cup full of water. What happens if you turn it all to steam? It will fill a large room because the gaseous state of water has a much bigger VOLUME than the liquid state. Exactly the same situation exists when you fire the laser at a plastic surface. If you use a low power beam and pulse the surface you will do two things First you will convert solid into gas which is hugely more volumetric than the solid t was a few microseconds earlier. Thus it will have to expand somewhere. Because this is not a through cut but an engraving, Secondly, the only place for those fumes to go is upwards like and erupting volcano. Once those fumes are in the air, the last thing you want to do is blow them back down onto your work with the air assist. The further your nozzle is away from the eruption zone the better and with virtually no air assist. What you do however need is a high velocity CROSS FLOW of air over your work to carry the fumes harmlessly away, If you use lots of power for engraving then there will not be a controlled upward volcanic eruption of fumes but a dramatic conversion of solid to gas that cannot expand upwards quickly enough,. Instead, it will explode sideways and be forced onto your work by the expanding gas pressure above it. NEVER take deep engraving cuts or you will coat your work with fumes regardless of air assist or not.. It is all very logical when you stop to analyse the situation. Sadly ,most do not and finish up with fume coated work. Take time to experiment and you will see the truth of this analysis. This is particularly true for Rowmatk material.
Best wishes
Russ
Love these videos! Your a hero
Hi At this stage of my learning journey I was happy to explain what I considered to be the differences between lenses. A little knowledge served me well until a couple of years later when I was searching for the smallest dot that lenses could produce.. I began to realize that some of the theory about lenses was exactly that and did not match up with practical observations I was making.. It got even more complicated when I did a 3 session test of lenses and finished up asking questions that I could not find answers to (see sessions 149,150 and 151)
I cannot find answers so I have started on a new series of investigations to see if I can REALLY understand how lenses operate in out machines. (see session 162) You will then realize how little I knew 3 years ago..
Best wishes
Russ
Damn it, I just bought a 4" lens and put it in today expecting it to cut better, and was very confused as to why it wasn't.
I knew that the beam it created would be bigger but I didn't properly think about the percentages involved in spreading out the beam just that little bit more, shot myself in the foot now.
Guess I'm buying myself a 38mm lens to cut 6mm MDF, who woulda thought.
Wish I had started watching this series a few weeks ago.
Hi Tom
At the time I did this video 7 years ago I was passing on all the accepted theories and practices about lenses. I was still just at the beginning of my laser learning journey and at that time this hobby was very niche and there was little or no help available on CZcams or WWW. That is the reason I started to record my learning experiences.
It was not until 3 years later when my lens collection was at 5, that I decided to do comparison cutting tests. By all lens theory and energy density principles, a 38.1mm lens should be a cutting monster. It wasn't. A cheap Chinese 50.8mm lens was much better. It even far exceeded the cutting ability of a VERY expensive 50.8 lens. WHY???
I added more lenses to my collection and did much testing, only confirming that demonstrable fact was not matching theory.
Here we are 4 years later and after seeking all sorts of advice from physicists, academics, optical experts and laser machine builders, none could explain how or why lenses could do this
czcams.com/video/vTEAm-01E1Q/video.html
It seems, just like daylight, it happens and is of no consequence why. Thus it It has fallen to me to find the reason on my own and it was only as recently as a couple of months ago that the last pieces of the puzzle were put in place. If you fast forward to this video all is explained.
czcams.com/video/kddSFO-iFNM/video.html
There may be some chunks of theory that I skip over so rather than tracking through all my learning videos to catch up, I have summarised my experience into an A to Z of Chinese lasers in this series of short videos.
laseruser.com/the-concise-rdworks-learning-lab-menu/
Best wishes
Russ
@@SarbarMultimedia So funny that we're all over here in the western world thinking the Chinese manufacturers are all putting in the lenses the wrong way and turns out they probably know what they're doing.
Did you come to a conclusion about why your cheap machine here was able to cut so well if it wasn't down to the 38.2 lens?
Your 40w seems to cut better than my 100w, I have ordered a power meter so I can tune everything up and make sure I get the most out of my machine, at the moment it does just seem a bit weak, currently cutting 6mm MDF at only 10mm/s and 3mm ply at 25mm/s, I had previously managed to get a 60w machine to cut 3mm ply at 30mm/s so something isn't right here.
Thanks for your presentations
LOL love the last 8 seconds of this video. :)
Once again, your video has answered my question.How to get a tighter stronger beam to cut through dense plywood like 1/8" 6 ply and 1/4" 5 ply. Bee struggling to get a clean through cut with the stock 2" lens even though I have it perfectly centered all the way through, but found I have to crank it to 75% at the software level with 80% set on the controller. Slowing it down winds up blowing out the bottom of the material too. The only thing not answered, do I need to change out the nozzle, or is it the same nozzle for all three? Going to try the 1.5 lens.
Hallo.
I have one question.
Do you habe soved the power loss problem with your laser tube?
I'm going to buy the same laser next week, thats why i'm asking.
Is this problem important by engraving something or only when you cut?
Wow that was really interesting, the opposite to what I believed was the case! I was considering a bigger lens upgrade at some stage won't now, thank you!
+patrick whelan
Hi Patrick
Thanks for comment. Several other people were asking me about lenses which is why I looked into the subject in more detail. Glad this has helped. This is not intended as a pun but I shall be looking into mirrors soon. A totally ignored subject.
Russ
Hi Russ! I really look forward to that! You are doing a great service for laser users! My machine is in safe hands because of you :) By the way do you have any ideas on how to silence the extractor pipe? I'm a little worried about my neighbours my new one is quite a bit louder than my old.
+patrick whelan
Hi Patrick
The answer is simple but doing it may be difficult if you live on a top floor apartment. The reason it's loud is because you are pushing high pressure air out of a small duct or straight out the fan. The principle of silencing is simple. You must allow the air to expand and slow down/lose most of its pressure/energy in an exhaust chamber from which it is allowed to escape at low velocity via a large area. A crude but simple to make example would be a plastic (or rubber) dustbin turned upside down. Sit a piece of 1"or 2" weldmesh upon 3 on- edge house bricks and put a layer of hollow fibre fill from an old duvet (glass fibre insulation will do but is not very eco friendly) on top. Cut your duct hole in the bin(side is better than top because it will create more noise baffling effect ) and put your upside-down bin onto the insulation layer and mesh. Tuck the insulation up into the bin but do not pack it tightly Now you will have expanded the air and distributed the flow over a large exit area (the fibres) but not choked the flow. Additionally any other noise from the fan will be absorbed by the ground as it turns through 90 degrees to escape. That's a crude example of the principle, now it becomes a test of your innovative skills to make it happen.
Good luck
Russ
Hi Russ, Thank you so much for that you have got me on the right track now. This will be next week's project I have access to plastic 200L Barrels so I'll use one of those as the exhaust chamber. I didn't really get the concept I tried putting some figure of 8 cut outs into the pipe to disturb the flow but unsurprisingly that didn't work lol tempting to build a filtration system into the barrel come to think about it. Luckily I don't live in a flat I have a 'detached' house but my garage wall is my neighbours house wall so we are very close and i do worry about upsetting them filtering would prevent the smell being a problem too. By the way redsail sold me my '130 watt' machine with reci S4 100watt tube and when i immediately contacted them thinking they had made a mistake they said that is what they do as it can do 130 at peak so is 130watt. As you can imagine I was very annoyed but nothing I can do and I soon got over it when i saw what it could do. I have had it cutting 20mm pine at 5mm/sec and 6mm ply at 30mm/sec so im very happy. Funny though I had to bring it down to 50% before it was running at safe mA for the tube. Just goes to show how these machines are almost set up to fail!.
+patrick whelan
Hi Patrick
Yep. Your S4 is a 100 watt tube , it's the S6 that's a proper 130watt tube. However, your machine is still fitted with a nice expensive tube. Your tube is capable of achieving 130 watts output but like all reputable tube suppliers RECI state running and max power as part of their spec. They supply these tubes with an expected life of 10,000 hours of "light-time". If you are a serious small business running 5 hours a day 5 days a week, that's about 1.000 hours per year. To give their 10 month warranty on this tube you must not run it at more than the recommended milliamps and it will still be outputting 100 watts after that period. This type of tube also contains a catalyst to help recombine the oxygen with the carbon monoxide when it becomes dissociated. This greatly extends tube life. The 130 watt bit of the spec is over-capacity to make sure that even with some small degradation, if you ran it 24/7 it would reach 10,000 hours in about 14 months, but at 10 months would still be delivering 100 watts. If you look at session 35 you will see how and why your tube output degrades and dies.
Back to your extraction. The smell is unlikely to be an issue because with a high airflow through the machine the fumes will be diluted by the volume. Just a note here. Make sure the air can flow FREELY through your machine. If you are in a closed workshop, ask yourself where is the airflow coming from? You will probably have to run with the workshop door open. Then check that there are sufficient holes in your machine case so that the air flow is not strangled at that point either.
Second thought. A plastic 6" (160mm) toilet waste pipe straight up above gutter level may solve both noise and smell problems at once and would be unobtrusive.
Regards
Russ
Hi Russ, Love your videos. Quick question on focal distance. Is the actual focal distance on a 1.500" lens = to 1.500" from the bottom of the lens or does one need to subtract 1/2 of 0.03149 (8mm) to get the optimal cutting point or, should one adjust the center of the distance to 1/2 of the material thickness, thus placing maximum cutting power to the center of the material? Seems I might have missed the video on adjusting focal distance.
+MarilynAnd Keith
Hi Keith
czcams.com/video/PUdEUxJH2_o/video.html
That's the one you need to watch. It's the empirical way to determine your focal distance from the end of your nozzle. It appears that different machines have different nozzle styles so that's why they normally supply you with a silly piece of acrylic on a piece of ribbon. It's absolutely meaningless to a newbie and there are no instructions in the manual to advise it's use (unless you found something when doing the English translation.) Although you were only tackling the RDWorks bit.
My lens drawings are technically wrong because the focal length is worked out from the top curved surface. However, it's not going to confuse you if you are trying to determine your FL because lenses are only available as 1" to 3" in 1/2" increments and 1" increments thereafter. The odd 3mm lens thickness wont stop you determining your lens FL..
Once you have determined your ideal nozzle to work surface distance. (mine is 6.5mm), you will use this distance for most situations, especially engraving where you often want the crispest dots. Some people advise dropping the work by 1mm to get a bigger dot and a slightly "softer" finish. It depends on the material and your preference. When cutting thick materials it's advisable to raise the work a little closer to the nozzle. 3 to 8mm acrylic maybe up by 1mm and for 12 and 15mm acrylic I raised it by 2mm (ie 4.5mm gap). So as you can see, nowhere near half the material thickness.
Regards
Russ
Thanks for the Video! Ordering a 1.5" lens for cutting my plywood..
+Ben Rogerson
Hi Ben
It is worth the extra to invest in a HQ lens. Natural uncoated Zinc Selenide lenses only transmit about 70% of the laser energy. Not because its absorbed or attenuated by the material but because the crystal structure is 30% reflective at this wavelength. An anti-reflective coating improves this to about 95% for standard cheap Chinese lenses but with more expensive coatings this can be as high as 99%. You will often see Chinese machines and lens suppliers mention that the HQ lenses are of USA origin. I think (just like Colonel Sanders and Coca Cola) they closely guard their recipe You might be able to buy one locally rather than China
Regards
Russ
+SarbarMultimedia how about the GaAs lens is it worth the extra money? Or should I look for a coated ZnSe lens?
+Ben Rogerson
I would stick with the HQ ZnSe. I believe the GaAs lens will not transmit visible light so if you wish to use a red laser pointer at any stage you will be in trouble.
Regards
Russ
Where did you buy the 38mm lens? My lens has fogged up badly (stupid experiments) and I can no longer clean it.
Thanks for the very informative series. You saved me a bunch of money and allayed a lot of my fears regarding these machines and their quality.
I have bought from here successfully several times
www.ebay.co.uk/itm/New-HQ-ZnSe-GaAs-Focus-Lens-For-CO2-Laser-Cutting-Machine-Diam-18-25mm-FL-1-4-/330769086309?var=&hash=item4d035fb765:m:mAiSYT53XXKKLeLwI6nRWrQ
18mm 19mm and 20mm diameter available so make sure you measure yours carefully before ordering. The morer expensive HQ coatings gain you another 2% efficiency so not worth the 50% extra, Stay with ordinary ZnSe.
Best regards
Russ
Hi Russ,
Please i have a question might seem weird!
Is there a way we can tell which is the 1.5" lens and the 2 " if we mixed them after we take them out the nozzle???
Hi Jay
Watch this video from about 7min czcams.com/video/UxfC9jbX6PM/video.html
In this video I am passing on the teachings of standard lens theory. . Much later in the series you will see me discover that all is not as simple as it seems . Spot size and energy density don't happen in the way as this simple model projects. There is a lot of lens theory which misleads us when it comes to cutting with a laser machine.
Best wishes
Russ
So if a short focal length has better penetration and also a finer cut, is there a practical use to ever use a lens with a longer focal length?
+Counselor_X
A question that I have asked myself also. However, I do believe that if you have a more powerful machine say 80 watts and beyond you will get a better cut with a 2" or 2.5" lens and because engraving (which is what these machines are sold as) is not all about raw power, it may well be that the "softer" cut gives a mor pleasing result. I don't know but that's exactly the sort of thing I plan to explore in my new engraving journey because I do have a 2.5 FL lens
Best regards
Russ
When you made this video, did you have the lenses flat side up or flat side toward the work? When I turn mine with the flat size toward the work, the cutting is absolutely brilliant.
Hi Marti
At this point in my learning journey I had already discovered that the Chines ship machines with the plano convex lens flat side up and that you het better cutting if you use it flat side down, It took a couple more years before I carried out in-depth research into lenses and discovered the reason for this interesting advantage.. My interest in photography and college physics ave me a pretty solid grounding in lens theory. It turns out that conventional theory does not work for our machines. You probably have a 2" focal length lens and your setting piece supplied with the machine is probably about 19mm wide? If so, flipping your lens will have decreased that focus setting to almost 17mm. Without boring you with science, if you want to do detailed engraving then flat side up is better and if you want to cut then flat side down is better. Here we are 4 years later than this video and I now understand so much more, It is sometimes embarrassing to watch me learning in these early days. BUT without any one to teach me , tiny steps and mistakes are all part of learning.. One simple question to finish.
Do you have a spare lens? suspect no. Your lens id the most vulnerable and the most essential part of the machine Always carry a spare. They are 3 weeks away and cheap if you buy from China . see www.cloudraylaser.com/products/china-pvd-znse-focusing-lens-for-co2-laser?variant=43422450056
Best wishes
Russ
Very nice and helpfull videos.
But i did not find the answer in the video
And i am almost afraid to ask this ,but has the curved side has to be up or down ?
Thank you
UP the curve side
Hi Russ! First of all i would like to congratulate you about your passion of finding what is wrong and how to fix it after detailed research. If i understood right, the air assist does not benefit the cutting process but the engrave process instead, correct? So if you are trying to achieve the deepest cut possible with a certain lens setup, you will not use air assist at all or just the minimum amount of air? For engraving i see that air assist is crucial in order to have less burning marks from fumes.
Sure thing is that to own and run a laser machine you have to know many things how they work and be prepared for many brainstorming sessions. I am saying that because many people think that a laser is simple as a printer..... Thanks in advance for your reply. Polis
Hi Polis'
3 things to understand about air assist
1) Never turn it off when your laser tube could fire. Even when you don't need much air assist , make sure there is still a whisper coming out of the nozzle. That way you will never fog up your lens.
2)You need just a bit more than a whisper when you are CUTTING acrylic. Acrylic does not CUT it EVAPORATES. Too much will cool the process down and reduce the cutting efficiency. You can use a little bit more for ENGRAVING acrylic
3) You need maximum air assist for everything else. Any CUTTING in wood or card products produces dense SMOKE because that is a BURNING process. Smoke absorbs IR radiation and so unless you keep the smoke clear from your IMMEDIATE cut area (in the groove) you will lose cutting efficiency and cause lots of charring.
Engraving wood will usually produce brown smoke sedimentation staining around your engraving. There is little you can do about this other than to mask off the surface and engrave through. Faster speed with lots of air helps but it's not a cure.
Thanks for your kind words
Best regards
Russ
Thank you so much for your detailed reply! I mainly cut plywood on a friends laser machine so have not the chance to fine tune it my self. So, i assume that max air assist will reduce also cutting depth on wood as it does on plexi, correct or not? Thanks!!
Hi Polis
Sorry if my answer confused. What I meant to say was minimal air flow for plexi glass but max airflow for EVERYTHING else. Smoke reduces cutting efficiency so you MUST get it gone. Max airflow for all wood products.
Regards
Russ
Thanks. Got it! So, only plexi glass because it is melting, does not like much air. It cools down the material making it harder for the laser beam to pass :)
Hi Polis
Still not quite got it right. Plexi is a rather special type of plastic. Most other platsics MELT when you heat them. If you fired a laser beam at a block of ice it would immediately turn to steam. Well, the same thing happens when you fire a laser beam at plexi, it does not melt but immediately turns to smelly gas. Too much air cools the plexi and reduces the speed that the plexi can vaporize.
Hope it'snow clear
Best regards
Russ
Not sure if this been commented on. I think I heard 25mA!? On a “50w max” tube? Guessing that your supply is putting out 15-16kV that’s close 70W of output power. (16kV * 0.025A * ~18% efficiency). Did you serious life of use issues?
Hi
There are recognised safe max normal working currents for these tubes. that runs with watts output and tube size
40watts will be 800mm long x 50mm diameter and run at 18mA
50watts will be 1000mm long x 50mm diameter and run at 20mA
60watts will be 1200mm long x 55mm diameter and run at 22mA
80watts will be1450mm long x 550 (somtimes 80mm) mm diameter and run at 24mA
For higher powers there will be differences between manufacturers but it is still safe to run 100 watts at 26mA
Reci have a reputation for being the best tubes. I am of the opinion they are expensive and VERY over specified, You can get the same quality tube at half the price. I have used and tested quite a few Reci tubes and only one has impressed me with performance.
If you run at higher than these typical currents the pink ionized nitrogen beam has sufficient energy to dissociate one of the oxygen atoms from the CO2 . Neither CO nor the free oxygen will create laser output so you will quickly consume the 10% CO2 within your tube and kill it. Even if you run at lower (or much lower) currents you cannot stop this natural process happening at a VERY slow rate. It is this mechanism that will eventually kill your tube. With an A grade tube you can expect 3 to 5 years of life, regardless of what the manufacturer promises.
Beware if you buy another tube , there are lots of B grade (relabled main factory QA failures) out there at tempting prices. They will be anything from nearly OK to near junk, it's a lottery,
Best wishes
Russ
What was your source for the lens?
+2020tesla
Hi Dwayne
www.ebay.co.uk/itm/391332816906?euid=24bf40a295d94c63ad8cd74208c7caee&cp=1
They are as good as the original fitted lens. and, I thought, reasonably priced. This is ebay uk but I suspect if you copy and paste the title into ebay.com you will get the same item. I made a bit of a mistake when I ordered them I selected 20mm diameter and my machine takes 18mm diameter. Was I going to send them back? No. I just ground 1 mm off all round with my disc grinder. Worked perfectly.
Regards
Russ
+2020tesla
If you're in the US, just search eBay for "laser focus lens 18mm" (assuming you OEM lens is 18mm). You'll find lots with focal lengths from 1" (25.4mm) to 4" (100mm).
Thank you so much for your expertise and taking the time to compile your information series.
I've got a K40 and 1400 bags of tea... Can you come round and sort out my machine? I'll pay for your travel to Oxford :0)
I have three problems with your request
1) This is just an engineering and video hobby for me in my retirement and I do not make "service/help" visits. If I started, where would I draw the line?
2) I know nothing about the K40 machine except that it is a very compromised little machine both mechanically and in it's controllability. That is why I never bought one 5 years ago when I made my buying decision. Apart from having a laser tube and 3 mirrors that where my knowledge of this machine stops.
3) I don't drink tea!!.
If you wish to add your disguised email (jimdotsmithathotmaildotcom) to another comment I will reply so that you can ask for help off line and supply pictures/video of your issues. I will try to help.
Best wishes
Russ
@@SarbarMultimedia Thanks Russ, you're a gent. Some freeware software has helped with the k40 since launch, allowing dithering and some other functionality. Unfortunately I can't use layers without upgrading the motherboard, which is a real shame and adds considerable time. Currently the laser is doing what i need it to do, albeit not at it's best, but your catalogued journey is helping greatly, thank you again. I've made an adjustable bed which although fundamental and £7 to make, is accurate and adjustable in 4 corners.
I think what I need to invest in is a lens housing that can hold a 38.1mm lens. I've looked around for your gold laser head but cannot find anything that I'm sure houses the 38.1mm lens. Any ideas on the latter? Then I'll let you off making you come to Oxfordshire and forcing tea on you.
@@DR87408 I do know that there are about 3 different head designs used on K40 machines. The basic design for the K40 is Chinese government approved (like all their machines) which is why they all look remarkably similar. The machine skeleton is approved but the details are down to the company building the design. They can use cheap or expensive parts depending on the market/profit they are trying to access.. If you have the link to the machine you bought it may have a few detail pictures for me to see.
Best wishes
Russ
@@DR87408 I think Russ is referring to the focal length of the lens rather than the diameter. This can be confirmed by looking at the video @ 8:30 where Russ is holding the 2" lens that arrived with a chip in it. Quite clearly although Russ refers to it as a 2" lens it is not 2" in diameter, and looks to be the more standard 20mm. I think what is maybe confusing is that you can also buy lenses that are 38mm in diameter... the cost though is significantly higher... a 38mm lens from Cloudray is about $250.
Have a look at this page and you can see what I mean... A 20mm diameter lens is available with a few different focal lengths.
www.cloudraylaser.com/collections/co2-laser-optics/products/usa-cvd-znse-focus-lens-dia-20mm-fl-50-8-63-5-101-6mm-1-5-5?variant=7645039394867
What am I missing, if it's a 38mm lense why it it being focused with a 6.5mm spacer? Shouldn't the spacer be closer to 38mm?
Also doing some reading on focus lenses. It seems the longer the focal length the deeper the cut. Maybe you are seeing a different effect because your laser is not powerful enough for a lenses with such a long focal length? Since with the longer focal length the "laser density" is weaker
There is some solid info from a very reputable company here
www.troteclaser.com/en-US/Laser-Machines/Accessories/Options/Pages/Focus-Lenses.aspx
Cheers
+Nathan Clark
Hi Nathan
I suspect that you are doing a lot of preparatory reading prior to getting a machine. If so then lenses can understandably be a bit confusing.
The 38mm focal length is the point where the all the energy is concentrated to a theoretical sharp point. It is measured from the curved side of the lens when it is facing the work. The lens is mounted in a holder inside the nozzle. There is about 32mm of beam path hidden inside the nozzle and its only the last 6mm which exits the nozzle. Thus from a practical point of view it make sense to set your work that 6mm distance from the end of the nozzle.
The details I have in my picture are absolutely correct and accord with the data on the Trotec site. The shorter the focal distance the better the lens will focus the beam to a smaller waist. The smallest cross section of the waist is called "spot size" For a fixed wattage beam you can do twice as much damage to the material by reducing the spot to 70% ( for example reducing the spot from 0.1mm to 0,07mm will double the energy density.........and be a sharper knife.)
I tried to remove the maths from my explanation but if you want a proper mathematical explanation of energy density, spot sizes and focal lengths then you need to visit
www.parallax-tech.com/faq.htm
Hope this will help remove the confusion
Best regards
Russ
+SarbarMultimedia Yes that makes total sense about the lens being up in the nozzle. It seems trotec says the longer the focal length the deeper the cut, but I though in your video you said the shorter focal length cut deeper. Maybe I misunderstood the results.
+Nathan Clark
Hi Nathan
The answer is both yes and no. Let me explain. The only thing that gets longer as the focal length increases is the length of the waist With that increased waist come the increased spot size and the lowering of energy density. That's physics, not an opinion. However you can get the energy density back up with a dramatic increase of watts into the lens. But what you have done is increase the cut width so you are now using a powerful axe rather than a precision scalpel. Here's where I can understand your misreading/confusion. That longer waisting means the the energy density CHANGES at a slower rate, thus you have the ability to cut thicker materials. Sadly with low power machines like we have you will never be able to pump enough power into a long focal length lenses to turn it into an axe.
However, fear not because my 38mm scalpel , if I set the focal point 2 or 3mm into the material, can cut through 15mm acrylic. You can see an example of this at the end of this video.
czcams.com/video/4qy5cPZWGj4/video.html
People with the standard 2" lens cannot achieve this even with 60 watts. Thus my contention is that for our typical 40 to 80 watt machines you will get a deeper cut with a 38mm lens. I could cut even thicker material with a 75mm focal length lens IF I had a 120 watt machine. It's pretty obvious that more power will give a deeper cut but I hope I have shown you that for any given power of machine there is an optimum focal length lens to get the deepest cut and when you run out of power , extending the focal length will cause the cut depth to DECREASE
You do not need high energy density for engraving that's why these machines are supplied with a 2" lens. These machines are sold as engraving machines that will cut, not cutting machines that will engrave
Great discussion. Thanks Nathan
Best regards
Russ
+SarbarMultimedia This along the lines of what I suspected- a lower powered machine can't take advantage of a longer focal length for cutting.
+Nathan Clark
Hi Nathan
I can now tell that you have completely understood the concept. Whatever power machine you have, there will be only one lens to give you the deepest cut. If you have 100watts available then that is probably a 2" lens but change up to a 2.5" lens and for 100 watts the cut will be shallower.
Who said owning one of these machines was simple?
Best regards
Russ
Головой вмял деревяшку.
Варвар.)
Very nice and helpfull videos.
But i did not find the answer in the video
And i am almost afraid to ask this ,but has the curved side has to be up or down ?
Thank you
+bart vandegoor
Hi Bart
The clue is in the drawings at the beginning of the video. I also found out fairly recently that my lens has been fitted the wrong way for months ( see czcams.com/video/TUJgBcb2xnQ/video.html at about 10 minutes in) Most machines are fitted with a simple plano-convex lens that is flat on one side (like the drawing) but I have heard of machines being fitted with a meniscus lens. This is not flat on the bottom but concave. You woulds still ft this with the convex side up (away from the work piece)
Thanks for your kind word
Regards
Russ
+SarbarMultimedia
Ok Thanks for your answer Russ.
Tomorrow i will check if it is a meniscus lens, the only thing i know it is a 63.5mm. , and the tube is a 80w Reci s2 model.
I love watching the video's . they are very helpfull.
Thank you again