The plexy you added to the module looks as a bad example. You are preventing good cooling of the module. And when you create sufficient smoke exhaust, you don’t need that. My cuts are always clean with the diode lasers I use, without something to block airflow.
Thanks for your comment and concern about my laser head overheating. Although the airflow may be reduced by about 20% it is also travelling across the endface of the heatsink body which it would not normally do. I have been testing the body temperature regularly and it stays at room temperature. I therefore think I have not compromised the module cooling. As for extraction, you may have noticed that this is not a normal diode laser machine but a an RF CO2 laser that has been temporarily converted to test these heads. The extraction is VERY efficient , even with the cover open (have you seen the frame by frame video at the end to see the extraction efficiency?) I am pleased that you do not have problems with your setup but I made these changes because the tar residue along the cut edges was present with or without air assist. I am not advocating this change for everyone, I am just illustrating my problem and how I went about solving it. I had no such issues when testing the 5 and 10 watt heads but that was because the long focal distances meant that the gap between nozzle and work was large. In the case of the 20 watt head this gap is about 6mm.
Thanks for sharing. In my experience an air assist reduce the risk of fire tremendous. The comparison of blowing out a sheet of paper towels with the conditions in a narrow gap is incorrect. It is the same as blowing out a candle and blowing on a campfire. The candle goes out, but the campfire is strengthened.
Hi I really appreciate it whan people take the time to watch and comment on what they see. Thanks for sharing your persona;l experience.which may depend on the brand of laser you are using and its focal distance. I never experienced issues with the 5 and 10 watt diodes but 20 watts seems to have an eklevated fire risk. I think you have misinterpreted my kitchen towel demo. The idea was to show that glowing red hot carbon cannot be blown out like a candle but by adding extra oxygen (air assist) you exacerbate the exotheric reaction and make the carbin glow nearly white hot like the campfire you describe. On the other hand there are parts of the cutting process that do benefit from the cooling effect of air flow. You will recall the end of the session where I posed two questions for you to think about. One was about the effects that air assist had on apparent cut width. It may seem impossible but the extra heating effect of air assist can also exist alonside a cooling effect. I will answer this conundrum in the next session. In the meantime I'm not sure you have understood the importance of carbon in the cutting process. The main costituents of wod are cellulose and lignin with about 10% of other non-structual materials like resin, oils/tars. Both cellulose and lignin are almost transparent at 455nm wavelenght see these graphs ruclips.net/video/ITQiwjAJysQ/видео.html www.researchgate.net/figure/UV-Vis-profile-for-a-Kraft-lignin-without-initial-lignin-and-the-same-sample-after-the_fig3_337842474 If they will not respond to 455 nm light they are technically as transparent as glass or clear acrylic. However, it is the 10% of other stuff in wood that can be stimulated by the light to heat up and cause the surface to darken and eventually create a carbon film. This carbon film then acts like a tunnelling machine because it rapidly absorbs the light energy thus heating the carbon film to near white hot. It is this white hot energy transfer film that precedes the cut and vapourizes the cellulose and lignin ahead of it., The laser beam is NOT cutting the wood. Understanding this mechanism of cutting illustrates the risk of fire if you keep the heat in one place for too long. In the next session I will investigate if there is any. cutting speed/depth advantage to jetting air into the kerf. Thanks again for your interaction on this subject as it does allow me to explain things in a way that my video may have skipped over. I am amazed at how complex cutting with a diode laser happens to be and I have never seen any scholarly works or manufacturer videos explaing how their product actually works . It's always just brands handing out free equipment to let others do their demonstrations/promotion for them.
@@TorteTS Hi I must alogize because I sent you an incorrect link. The top left graph is the one I wanted you to see. www.researchgate.net/figure/UV-visible-absorbance-spectra-of-the-aqueous-phase-after-a-cellulose-films-and-b-PHB_fig5_322879134#:~:text=Additionally%2C%20the%20absorption%20peak%20at,at%20304%20nm%20%5B29%5D%20.
Fantastic Series. I will have to back up and watch them all. Couple of questions; You increased the effectiveness by reducing the hole size of the nozzle to 1.5 mm , how about 0.5 mm or say a more directed air stream (may be mounting a hypodermic needle). Also to increase the carbon tunneling effect would increasing the oxygen concentration from 21% in air to higher concentrations be effective since the burn may be oxygen limited? Thank you so much for your thorough and thought provoking explanations.
Hi John There is balance to be struck between pressure, airflow, orifice diameter and distance to the work. The priciple is much like ohm's law except electrical is not compressable whereas air is. For any given pressure DIFFERENCE across an orifice you will create a specific air flow, however, unlike current, water or oil, as soon as it escapes from the orifice, air instantly expands and just like paint spray it will form a huge cone. The greater the pressure difference across the orifice the more explosive the expansion will be instantly it exits the orifice. Yes, you will get more flow through the orifice with higer pressure but by the time it jumps across the gap to the work and expands it may be pretty ineffective, You will notice I checked the jetting effect of my orifice with a shallow lid of water. It is virtually impossibe to create laminar flow (a nice straight jet) with gas because of the expansion issue, so there is a compromise to be made My relatively low presure pump (3psi max) is probably creating no more than 1psi across the orifice so the gas does not expand rapidly upon exit to free air. Thus my cone of flow is narrow upon hitting the work and effective over a small zone. If you make the orifice smaller you will get less flow but more jetting for a short distance if you have sufficient pressure and ultimately a greater expansion cone. As I said, this is very much a compromise. I may not have achieved the absolute sweet spot but it's doing well as air assist and great as a lens protector. The priciple of adding more oxygen to the cut is used in metal cutting of mild steels as this aids the oxidation process within the cut (just like an oxy acetylene gas axe). However, metal does not ignite like any of the combustable materials we use on a diode laser. In session 20 I demonstrate what happens if you do as you propose.
@@SarbarMultimedia Thanks so much for the response. I agree there is definitely a tradeoff. Bridging the distance from the air / laser nozzle to the material (6 to 8 mm) and then getting the air down in the small gap is challenging. I was just thinking if you make that gap smaller with a nozzle design that was longer that may possibly be more effective in delivering the air to where the reaction is taking place. If you need more air for cooling that is really a separate issue that could be addressed with side vents. Love your content!
@@johnwagner7853 Hi John Thanks for the interest. I generally only fix issues that the designers of equipment have obverlooked or not understood . My solution here works for me but the principles I have demeonstrated can be adpted for your own equipment . Although my main goal is self-education on this little understood technology, I hope that a few, wanting to go futher than just fiddling with the Lightburn parameters, will be stimulated to explore their own machies in more depth. Yout thoughts already tell me that you are one of those few.. Salutations!!
such a good method for exploration, i just love your lectures
The plexy you added to the module looks as a bad example. You are preventing good cooling of the module. And when you create sufficient smoke exhaust, you don’t need that. My cuts are always clean with the diode lasers I use, without something to block airflow.
Thanks for your comment and concern about my laser head overheating. Although the airflow may be reduced by about 20% it is also travelling across the endface of the heatsink body which it would not normally do. I have been testing the body temperature regularly and it stays at room temperature. I therefore think I have not compromised the module cooling.
As for extraction, you may have noticed that this is not a normal diode laser machine but a an RF CO2 laser that has been temporarily converted to test these heads. The extraction is VERY efficient , even with the cover open (have you seen the frame by frame video at the end to see the extraction efficiency?)
I am pleased that you do not have problems with your setup but I made these changes because the tar residue along the cut edges was present with or without air assist. I am not advocating this change for everyone, I am just illustrating my problem and how I went about solving it. I had no such issues when testing the 5 and 10 watt heads but that was because the long focal distances meant that the gap between nozzle and work was large. In the case of the 20 watt head this gap is about 6mm.
Interesting stuff, thanks! :)
Thanks for sharing. In my experience an air assist reduce the risk of fire tremendous.
The comparison of blowing out a sheet of paper towels with the conditions in a narrow gap is incorrect. It is the same as blowing out a candle and blowing on a campfire. The candle goes out, but the campfire is strengthened.
Hi
I really appreciate it whan people take the time to watch and comment on what they see. Thanks for sharing your persona;l experience.which may depend on the brand of laser you are using and its focal distance. I never experienced issues with the 5 and 10 watt diodes but 20 watts seems to have an eklevated fire risk. I think you have misinterpreted my kitchen towel demo. The idea was to show that glowing red hot carbon cannot be blown out like a candle but by adding extra oxygen (air assist) you exacerbate the exotheric reaction and make the carbin glow nearly white hot like the campfire you describe. On the other hand there are parts of the cutting process that do benefit from the cooling effect of air flow. You will recall the end of the session where I posed two questions for you to think about. One was about the effects that air assist had on apparent cut width. It may seem impossible but the extra heating effect of air assist can also exist alonside a cooling effect. I will answer this conundrum in the next session. In the meantime I'm not sure you have understood the importance of carbon in the cutting process. The main costituents of wod are cellulose and lignin with about 10% of other non-structual materials like resin, oils/tars. Both cellulose and lignin are almost transparent at 455nm wavelenght see these graphs
ruclips.net/video/ITQiwjAJysQ/видео.html
www.researchgate.net/figure/UV-Vis-profile-for-a-Kraft-lignin-without-initial-lignin-and-the-same-sample-after-the_fig3_337842474
If they will not respond to 455 nm light they are technically as transparent as glass or clear acrylic. However, it is the 10% of other stuff in wood that can be stimulated by the light to heat up and cause the surface to darken and eventually create a carbon film. This carbon film then acts like a tunnelling machine because it rapidly absorbs the light energy thus heating the carbon film to near white hot. It is this white hot energy transfer film that precedes the cut and vapourizes the cellulose and lignin ahead of it., The laser beam is NOT cutting the wood. Understanding this mechanism of cutting illustrates the risk of fire if you keep the heat in one place for too long. In the next session I will investigate if there is any. cutting speed/depth advantage to jetting air into the kerf.
Thanks again for your interaction on this subject as it does allow me to explain things in a way that my video may have skipped over. I am amazed at how complex cutting with a diode laser happens to be and I have never seen any scholarly works or manufacturer videos explaing how their product actually works . It's always just brands handing out free equipment to let others do their demonstrations/promotion for them.
@@SarbarMultimedia Thank you for your detailed feedback. And yes, there are not much detailed information about it.
@@TorteTS Hi
I must alogize because I sent you an incorrect link. The top left graph is the one I wanted you to see.
www.researchgate.net/figure/UV-visible-absorbance-spectra-of-the-aqueous-phase-after-a-cellulose-films-and-b-PHB_fig5_322879134#:~:text=Additionally%2C%20the%20absorption%20peak%20at,at%20304%20nm%20%5B29%5D%20.
Fantastic Series. I will have to back up and watch them all. Couple of questions; You increased the effectiveness by reducing the hole size of the nozzle to 1.5 mm , how about 0.5 mm or say a more directed air stream (may be mounting a hypodermic needle). Also to increase the carbon tunneling effect would increasing the oxygen concentration from 21% in air to higher concentrations be effective since the burn may be oxygen limited? Thank you so much for your thorough and thought provoking explanations.
Hi John
There is balance to be struck between pressure, airflow, orifice diameter and distance to the work. The priciple is much like ohm's law except electrical is not compressable whereas air is. For any given pressure DIFFERENCE across an orifice you will create a specific air flow, however, unlike current, water or oil, as soon as it escapes from the orifice, air instantly expands and just like paint spray it will form a huge cone. The greater the pressure difference across the orifice the more explosive the expansion will be instantly it exits the orifice. Yes, you will get more flow through the orifice with higer pressure but by the time it jumps across the gap to the work and expands it may be pretty ineffective, You will notice I checked the jetting effect of my orifice with a shallow lid of water. It is virtually impossibe to create laminar flow (a nice straight jet) with gas because of the expansion issue, so there is a compromise to be made My relatively low presure pump (3psi max) is probably creating no more than 1psi across the orifice so the gas does not expand rapidly upon exit to free air. Thus my cone of flow is narrow upon hitting the work and effective over a small zone. If you make the orifice smaller you will get less flow but more jetting for a short distance if you have sufficient pressure and ultimately a greater expansion cone. As I said, this is very much a compromise. I may not have achieved the absolute sweet spot but it's doing well as air assist and great as a lens protector.
The priciple of adding more oxygen to the cut is used in metal cutting of mild steels as this aids the oxidation process within the cut (just like an oxy acetylene gas axe). However, metal does not ignite like any of the combustable materials we use on a diode laser. In session 20 I demonstrate what happens if you do as you propose.
@@SarbarMultimedia Thanks so much for the response. I agree there is definitely a tradeoff. Bridging the distance from the air / laser nozzle to the material (6 to 8 mm) and then getting the air down in the small gap is challenging. I was just thinking if you make that gap smaller with a nozzle design that was longer that may possibly be more effective in delivering the air to where the reaction is taking place. If you need more air for cooling that is really a separate issue that could be addressed with side vents. Love your content!
@@johnwagner7853
Hi John
Thanks for the interest. I generally only fix issues that the designers of equipment have obverlooked or not understood . My solution here works for me but the principles I have demeonstrated can be adpted for your own equipment . Although my main goal is self-education on this little understood technology, I hope that a few, wanting to go futher than just fiddling with the Lightburn parameters, will be stimulated to explore their own machies in more depth. Yout thoughts already tell me that you are one of those few.. Salutations!!