Air assist, Cone v Tube?

[Dave Johnson29]

Hi All,

I am thinking of adding air assist to my laser. I have shop air on supply and I would like to get opinions on the different methods of air delivery.

From an Engineering standpoint I favor the cone as it seems the better approach being a more direct method of air delivery.

With Epilog's tube, does it just blow a large volume of air in the general direction of the beam spot to blast away stuff?

Obviously the cone will be more machine time, but if it is quite a bit better than the tube, then I do not mind. However if there is not much difference between the cone and tube then the tube is going to win out.

Thoughts, opinions and suggestions gratefully accepted for cogitation and application.

[Jack Harper]

Not only does the cone increase the pressure and focus on the material, it also reduces the opening for debris to bounce back on the lens. If you are going to add air, why not also add air dams to your mirrors while you are at it? Just make sure you have an air dryer and good air filters on your shop air!

[Dave Johnson29]

If you are going to add air, why not also add air dams to your mirrors while you are at it? Just make sure you have an air dryer and good air filters on your shop air!

Thanks jack,

I have a pretty aggressive extraction system and my open mirrors have not clouded or dusted up in the past 2 months or so since the last clean. I have the luxury of very low humidity and clean country air. :)

I do have a refrigerated dryer for the shop air so that would not be a problem so I think I will just opt for the air assist.

Thanks for the comments I am still leaning very much towards the cone.

[Michael Simpson Virgina]

I think an after market conical system is a major undertaking. And if you still have any kind of warranty forget about it.

[Dave Johnson29]

I think an after market conical system is a major undertaking.


Mike, you are going to kick yourself here. :)

My Signature. "Shop full of metalworking CNC machines," when I said, "make" I meant "make!" :D:D



And if you still have any kind of warranty forget about it.


My Signature, "ULS-1700 open frame laser," (Circe 1992)
Now, ULS may give good warranties but I suspect mine may be a toot outside even their envelope. :D:D

OK, back to the serious side of things.
Also on the warranty issue, while the Magnusson-Moss act is still alive and living, a correctly fitted cone kit would not affect any valid warranty.

[James Stokes]

I have 2 laser one has the cone assist and the other one is the Epilog tube. The cone does a much better job in my opinion. The only thing is your alignment has to be good or the beam is going to hit the cone. I als do not have to clean the lens every day using the cone, it definatly keeps the lens cleaner.

[Michael Simpson Virgina]

What I was getting at is that if you are under warranty making a conical system is going to void it. I do know on the ULS conical system it has to run all the time (Even when rastering) or the lens will over heat.

One of the things I liked about the ULS was the conical air assist but I did not like the idea that there was no solenoid so it spit air 24/7 unless you manualy turned the air on and off. You can get a nice 1/4 NPT air solenoid for less than $100 but you will still have to manually turn it on or off unless you could find some sort of control point on the laser.

Also I thought I would add this. I did not notice much of a difference between the cuts I got from the ULS conical system and that on the Epilog (Non conical). If anything the cuts on the ULS were not as good. That said we were cutting Acrylic I am not sure the same could be said for the nastier items like PCBoards or MDF. I would think that if you could dial in the conical you could fine tune it to a much higher degree.

[Scott Shepherd]

I do know on the ULS conical system it has to run all the time (Even when rastering) or the lens will over heat.

It doesn't overheat the lens because of the cone, it creates a vacuum and it sucks debris onto the hot lens like a magnet and if you're not paying attention and catch it quickly, it will crack your lens because of the build up on the lens.


One of the things I liked about the ULS was the conical air assist but I did not like the idea that there was no solenoid so it spit air 24/7 unless you manualy turned the air on and off. You can get a nice 1/4 NPT air solenoid for less than $100 but you will still have to manually turn it on or off unless you could find some sort of control point on the laser.

There is an option that controls this. My air assist is controlled on and off at the control panel, by color.


If anything the cuts on the ULS were not as good.

That wasn't a function of the machine, it was a function of the settings used to cut the acrylic.

[Dave Johnson29]

What I was getting at is that if you are under warranty making a conical system is going to void it.

Mike,

That's why I mentioned the Magnusson-Moss act. It is highly unlikely that a correctly fitted and operated after market conical could void any warranty.

The M-M Act puts the onus of proof on the manufacturer to establish that the after market item caused a failure. They cannot arbitarily cancel the warranty just becaue something non standard is fitted to anything.

[Michael Simpson Virgina]

On the heating issue that's what I was told me by the ULS dealer. But Because he was wrong on other things I suspect he could have been in error on this point as well.

Also there are two types of air assist systems on the ULS machines. Manual and computer controlled. The manual is just like I described. The computer controlled is a better system (The one you have)

The problem is that the computer controlled system is over $2000 extra and is not offered on the VLS models. Only the PLS and above models.

With the computer controlled system you can tweak your air settings and they can be assigned for each color. If ULS would have offered this option on the VLS models I may have considered them.

One more thing. ULS does offer the option to install a tube just like the Epilog has. This was done for the users who do a lot of real wired shapes and the conical attachement can get in the way. This option also lets you turn off the air assist (manualy) when you raster as it does not create the suction you described.

[Dave Johnson29]

It doesn't overheat the lens because of the cone, it creates a vacuum and it sucks debris onto the hot lens like a magnet


Scott,

I really cannot see how that can happen. If there is no air coming through then how can anything be sucked up into the cone and on to the lens?

I can see how the lens could overheat with a cone and no air flowing through it. That's probably why ULS run air all the time to cool the lens because it is mostly enclosed. With the Epilog and other non cone types, the lens is open to the cabinet temperature and circulation.

[Rodne Gold]

Air coincident with the beam is not always the most desireable. The most common reason for using a cone is to pressurise the final optics and thus keep em clean. We use both systems on our lasers , 3 of em using cones , 3 using nozzles. Both work quite well...HOWEVER there are upsides and downsides.
The directable nozzle is capable of directing dross away from the engraving area and capable of ejecting melt etc obliquley thru the cut , sometimes to good effect . But it is very easy to knock the nozzle out of alignment making air assist less than optimal. Sometimes one has to move the cone or nozzle out the way when engraving stuff with lips etc , its easier to do with a nozzle than a cone..remove the cone and you dont have air assist,
It is also IMHO a lot easier to add an aftermarket nozzle system then seal and pressurise a lens box and it is more configureable as to nozzle exit size and thus better control of air pressure at the cut.

One of the reasons we dont like a pressurised lens/mirror cavity is that we have lost lenses due to water trap failure and moisture/oil on the lens itself so we are totally anal about clean dry air to the cone type systems , and far less concerned about this to the nozzle system.

[Robert Ray]

On the 4000 watt machines we use at the day job, I measured the beam profile with a Primus measurement tool and found that with the purge air off, the beam gets wide, and the hot part spreads out randomly from the center, reducing beam density by up to 50%.

As I turn the assist air up, the center of the beam gets hotter in the center of the profile, and the diameter of the spot gets smaller. This is measured without a focusing lens, when the beam is 10mm wide.

At home I have nozzles on my Laser Pro systems, and keep the purge air turned up for the finest cuts. I have turned down the air to cut paper without blowing parts away, then forgot to turn it back up to discover incomplete cuts and extra charring.

-Robert

[Rodne Gold]

I cant quite see how air assist would affect beam width or quality unless its cooling an optic or mirror or the pressure of the air is somehow moving an optic or seating it better?

In terms of incomplete cuts , often air assist does a few things , it can act as an oxygen source to promote better vaporisation (kinda like a bellows)
and it can blow away smoke , dust and byproducts of vaporisation thus leaving the beam a "clean" area to work on with no interference.

[Scott Shepherd]

Scott,

I really cannot see how that can happen. If there is no air coming through then how can anything be sucked up into the cone and on to the lens?

I can see how the lens could overheat with a cone and no air flowing through it. That's probably why ULS run air all the time to cool the lens because it is mostly enclosed. With the Epilog and other non cone types, the lens is open to the cabinet temperature and circulation.

Dave, I'm only going by what's in the manual and what the factory has told me. Perhaps you are thinking of it in a vector situation. Imagine if it's rastering, the big hole in the side of the mirror assembly moving back and forth at high speeds, then the small hole in the nose cone, I'd imagine the large hole flying one direction creates negative air pressure and sucks it up the small hole. Moving the other way probably pushes air out.

I know it happens because I've done it. I've left the cone on without air and rastered and it just about ruined my lens. The lens is hot, the debris gets sucked right up into it and it fuses onto the lens. I had a real time trying to get the melted plastic off the lens. It was also completely black, so I imagine it was only minutes away from cracking.

[Dave Johnson29]

I cant quite see how air assist would affect beam width or quality unless its cooling an optic or mirror or the pressure of the air is somehow moving an optic or seating it better?


Rodney,

On some lase optical test beds, compressed air is used to minutely focus a beam. Sort of a final tweak to focus.

Having said that I am with you on air assist doing the same. The pressure change with an open ended tube or cone (IMHO) would not be high enough to make a difference.

[Dave Johnson29]

I'm only going by what's in the manual and what the factory has told me.


Hi Scott,

I assumed you left the hose connected even when not in use and as such it would be a sealed system.

What you say is highly probably with the air inlet hole scooting left and right. It certainly could create flow in either direction. Maybe block off that air inlet opening when you remove the air assist tubing. With that "scoop" end closed it should prevent air movement within. However then lens heating may be an issue with no cooling air.

Why not run air assist at a lower pressure rather then removing it?

[Scott Shepherd]

Dave, it's not made like that and there are no tubes to remove. The mirror assembly that flys back and forth has an internal system that puts air in at the lens area. So the air is actually coming through the lens/mirror assembly area, and it's let out just below the lens, which goes down into the cone. So there is no unhooking, hooking up of it all, it's all internal. The opening I'm speaking of is the actual hole in the side of the assembly that lets the beam come in and hit the mirror. Probably not going to work to well if I block that off :)

Why would you not leave the air on low all the time? You can, but in my case, I used the air assist to vector cut some material, forgot I had the nose cone on there, sent the next job over with the air turned off, and didn't pay attention. I suddenly saw the engraving quality disappear, and after pondering what the problem was for a minute, I decided to finally stop it. When I did, that's when I realized the air was off, the nose cone on, and the lens was trashed.

[Dave Johnson29]

The opening I'm speaking of is the actual hole in the side of the assembly that lets the beam come in and hit the mirror. Probably not going to work to well if I block that off


So the goop is getting in on the top side of the lens and nothing to do with the cone?

:) Depends how dilligent you are...

http://www.laserresearch.net/shopping/shopdisplayproducts.asp?id=278

To wit...
"W Series windows are often used as vacuum seals in front of the output coupler or in other parts of a system that require sealing of vacuum or high pressure. ZnSe is typically used for this application and can be provided coated or uncoated. AR coating provides >98.5% transmission and reflection <.25% per surface at 10.6 microns. Absorption values do not exceed .25%."

[Bob Davis]

We have an Epilog with a tube and a GCC with a nozzle, and our experience is that the lens in the nozzle machine needs far more regular cleaning than the tube lens. And I have no idea why.
The result is counter-intuitive, but it is definitely the result in our workshop.

[Rodne Gold]

The only reason I can think of that a pressurised lens box might get dirty quickly is if there is some sort of venturi effect whereby the airstream is causing a low pressure area somewhere that is hoovering up smoke and debris and passing it thru the lens box.
There might be a localised low pressure area at the bottom surface of the lens due to the airstream flowing round the lens mount which is perhaps sucking in smoke from round where the nozzle fits into its slot or from another "leak" source in the system?

[Scott Shepherd]

Dave, it's not getting crud on the top side of the lens, it's the bottom side.

The airflow output in below the lens. In these photos, you can see the outlet for the air inside the head. This is about 3/16" below the lens itself. The slut in the second photo is where the lens slides into. I'm not making this stuff up, it's in the manual (don't run it without the air on) and supported by tech support, as well as actual experiences I had. They told me "don't do it without air, or it will suck debris into the lens" and I did it, it sucked debris into the lens. That's all I know. Don't know why, don't care why, but exactly what they told me would happen did happen, so there must be something happening there.

[Dave Johnson29]

I'm not making this stuff up, it's in the manual (don't run it without the air on)

Whoa back Scott,

Not suggesting you are making it up, I am just trying to understand the problem. If I build my own I would like to design around the issue if possible.

Since design time, CNC machine time and material are not issues it does not have to be a cost effective thing as it is a one-off for my laser. That's why I am trying to totally understand why there is a problem before I build one and find I have designed the same problem in to it.

It might be there is no better way, but there also may be a better way.

I apologize if you think I am challenging you, it is just a function of the Mechanical Design Engineer mindset to evaluate a design problem. I like getting to the nub of things and sometimes that has me coming off a little brusque in the search for accuracy without diversions.

If I had your ULS lens-head in my hand I could probably figure out the problem in minutes, or at least a solution to get around it. But, I am limited to question and responses based upon your replies.

Thanks for taking the time for the pics. I am not sure I can see what's what but I guess I will proceed with the cone version. In fact I suspect I will have air flow over the turning mirror and boith sides of the focusing lens and a Zn-Se window for the beam inlet.

I can run a whisper flow of air when air-assist is not needed. I can control that from the computer via a USB port and small VBA script in Corel.

[Dan Hintz]

Steve,

When Paul was here to set up my machine, I mentioned your belief of what happens when the air assist isn't turned on and the cone is attached. He strongly disagreed and said it was simply overheating of the lens due to lack of airflow. That's my belief, as well, and I cannot come up with any method in which debris could be sucked onto the lens through the cone. If it was a cavity opened only at the cone tip, the heated air would expand, pushing out any contaminants in the cavity (only to a degree as we're talking about a very small amount of air). If the cavity had openings at both ends, the limited heating of the cavity air would not provide enough of a draft to pull in contaminants of any real bulk.

[Scott Shepherd]

Put your nose cone on, turn the air off, raster some blue or red rowmark and then call me when your lens is broken. It'll be broken because it'll be completely covered in plastic residue. That's not a crack due to overheating, that's a crack due to overheating BECAUSE it's covered in melted plastic.

Trust me guys, I've had to get the plastic off the lens. It didn't get their magically. It happened in minutes.

Trust me, as hard to believe as it may be, I can promise you it's a very real condition. Anyone who wants to buy me a lens is welcome to have me video tape it happening as we destroy the lens.

[Scott Shepherd]

I've saved you the expenses. Not sure what else I can do to prove this is happening (or why I have to prove it), but here's the run down.

Just ran a few hundred pieces from black ada material, 1/8", all vector cutting, with air assist and the nose cone. Pulled the lens, it's perfectly clean. No dirt at all.

Turned the air off, cut 2 of the very same pieces without air, with the nose cone on, pulled the lens and it's starting to cake up with debris. Not sure how else I can put it. Either you believe it or you don't.

Here's the lens after being cleaned.Notice the center is not cloudy and it's an even finish across the center.

http://www.customengravingandsigns.com/photos/lens2.jpg

Here's the same lens after less than 2 minutes of run time. Notice the center of the lens is clouding up. You can imagine 2 more minutes of this and then lens would be totally black.

http://www.customengravingandsigns.com/photos/lens.jpg

[Robert Ray]

I cant quite see how air assist would affect beam width or quality unless its cooling an optic or mirror or the pressure of the air is somehow moving an optic or seating it better?


I thought I would share a couple Primus scans of a 3300W CO2 beam, taken without the focusing lens installed. The beam is about 11mm in diameter.

The way the Primus measures is it has a mirror on the end of a wire, that spins in a circle, passing quickly through the beam path at 2500RPM's, as another motor moves the spinning one through the beam path at about 2mm/sec. The mirror scans a series of arcs through the beam path, reflecting on sensor arrays, and the software puts together a beam profile.

With the airflow set as low as I dare, I captured a scan. I only averaged 2 scans where I would normally do 4, because I did not know how far the beam would move, and as airflow changes the beam both walks away, and the hot part of the beam that does the actual cutting distorts. I run risk of the beam cutting through the side of the Primus measurement head if the beam walks too far.

The second scan is with the airflow turned back up to normal, and you can see that the hot spot of the beam is more symmetrical. I used an average of 4 scans of the beam, but 2 averages shows the same thing.

The low airflow condition would make the hot part of the beam spread out enough that even after focusing, the energy density is about 25% lower in this case.

I cannot measure what the effects are on our lower powered lasers, but I suspect things scale down. I feel the nozzle would be best for the beam only because of seeing the airflow effects on the higher powered lasers. One thing is for sure, that airflow has an effect on the beam.

The other concern I read of is water on the lens... I have also bubbled water on my lens a couple times, so I watch for that. I put an air seperator inline with my air assist, and cracked it open to bleed off moisture, then opened my air assist restrictor valve on the engraver all the way open.

[Rodne Gold]

Please explain to me the physics of of how airflow will shape a laser beam?

[Robert Ray]

Please explain to me the physics of of how airflow will shape a laser beam?

I wish I could explain it better Rodney, but i'm just the technician who runs the tests, and hands the data to the eggheads upstairs. All I know is that we need to use CDA (clean dry air) or N2 for the CO2 lasers.

Also, isopropyl alcohol in the air messes up the beam real bad too. I once cleaned the system with isopropyl alcohol, and ended up causing a beam dump to explode because the beam wandered too far from the water cooling part.

-Robert

[Dan Hintz]

Super-heated air will act as a focusing rod due to differences in angle of refraction... in essence, you're creating a type of self-regulating laminar flow without the tubes.

[Rodne Gold]

Dan , its coherent light , the optics and not air assist will focus it to a point , the idea being thrown about here is that air assist in some way shapes the beam characteristics.
This air isnt superheated anyway , and the laser itself wont superheat it.

[Mike Null]

I'll add my two cents here as well. On my Trotec I don't use air assist for rastering as it indeed causes the cone and the lens to collect debris at a faster rate than if it is off. When I have encountered a poor engraving result it is almost always due to the cone filling with debris and the lens being dirty.

I take pretty good care of my optics and in 12 years have never needed to replace any.

The other thing I've noticed is that I have to use more power when I use air assist to get the same result.

[Dan Hintz]

Dan , its coherent light , the optics and not air assist will focus it to a point , the idea being thrown about here is that air assist in some way shapes the beam characteristics.
This air isnt superheated anyway , and the laser itself wont superheat it.
Compared to the surrounding air, the air directly surrounding the beam is heated, creating an optical "tube". Coherency is only relevant so far as the phase angle going unchanged, but the effect would be the same (albeit to varying degrees) with incoherent light. Change the cone hole shape and I bet you'll see some interesting effects on the beam shape.

[Robert Ray]

Please explain to me the physics of of how airflow will shape a laser beam?

OK, one of our scientists gave me the full explanation today. It turns out the laser's beam is very succeptable to organic contamination. In other words Carbon in the air is what makes the beam diverge.

When we use compressed air or nitrogen purge through a nozzle, what is happening is we are pushing aside organic molecules, so the laser can travel straight through to the work. Smoke in the air will cause the beam to get wider, as well as alcohol fumes from cleaning, which also contain carbon.

So it's not the airflow that is shaping the beam, but rather a way to prevent organic molecules from absorbing the laser energy before it hits the work.

So the most important thing is that you have enough exhaust to quickly remove smoke, then the purge air, either by tube or nozzle to keep smoke out of the beam path.

[Dan Hintz]

OK, one of our scientists gave me the full explanation today. It turns out the laser's beam is very succeptable to organic contamination. In other words Carbon in the air is what makes the beam diverge.

When we use compressed air or nitrogen purge through a nozzle, what is happening is we are pushing aside organic molecules, so the laser can travel straight through to the work. Smoke in the air will cause the beam to get wider, as well as alcohol fumes from cleaning, which also contain carbon.

So it's not the airflow that is shaping the beam, but rather a way to prevent organic molecules from absorbing the laser energy before it hits the work.

So the most important thing is that you have enough exhaust to quickly remove smoke, then the purge air, either by tube or nozzle to keep smoke out of the beam path.
Robert,

As I was nearing the end of my reply below, I realized I wasn't quite sure which side of the argument you were on, so read it more as an intent to clear up misconceptions rather than an attack of any one point of view.


---

This explanation doesn't hold air (pun intended). Typical air is less than 400 ppm CO2 (not individual carbon molecules), and even so any contamination in the air (organic or otherwise) can cause beam divergence.

The use of compressed air or nitrogen is for reduction of substrate contamination (oxidation), prevention of burning, etc. Any cleaning alcohol in the nozzle cavity would evaporate within a few seconds of turning on the laser after being cleaned. Smoke can be heavily carbon laden, but that will depend upon what was being burned, and the compressed air should be pushing that out of the way.

If the path is clear, the beam will diverge less, but there is more at work than just the clearing of the path... the beam shape is also heavily affected by what I've mentioned previously, particularly for multi-kW systems.

[Rodne Gold]

Sheesh , I give up - yeh , air assist changes beam shape - a sharp hole in a cone will give you the same effects as changing your lens to a shorter one .....

[Dan Hintz]

Sheesh , I give up - yeh , air assist changes beam shape - a sharp hole in a cone will give you the same effects as changing your lens to a shorter one .....
Rodney,

You're making assumptions about kW systems based upon your experience w/ 25W systems... think of it in terms of quantum and macro. No one here ever said hole size is the same as changing a lens. Maybe you're having a bad day/week, but that's just being melodramatic, don't you think?

[Robert Ray]

I'm sorry if anyone read anything else into my posts, I did not intend anything other that finding out exactly what nozzle vs blow tube air really does, and to share my findings. I tried to relate it to obversations and measurements taken from the big lasers to the little lasers. :o

-Robert

[Rob Bosworth]

I have been a little reluctant to get into this.

Here's from my experience. Using pressurized gas assist can change the shape of a lens. When we first started using different gasses to accomplish different things processing materials with a laser, we found that our focusing properties of the laser beam changed. We thought we were changing the dynamics of the laser beam by adding pressure. The more pressure we used, the more our focus point and spot size changed. WOW. We finally realized that the higher the assist gas pressure, the more we were actually distorting the lens itself. The optic itself actually distorted from too much pressure. So we went to thicker lenses, and that problem seemed to disappear, until we got to a pressure point that blew the thicker lenses out of their mounts.

If you change the configuration of the nozzle of an air assist cone, it changed what was happening in and under the plume in the laser process. A nice smooth, clean opening in the cone, and the processed materials had very "regular" results. If the air assist gas nozzle wore down on one side, or junk built up unevenly around the opening, then the material being processed showed different results. It had to do with airflow and turbulence. I do not think we ever found the laser beam changing configuration or dynamics.

There has to be a difference in the results of a material being processed with a laser if you are using a coaxial air assist cone or blowing air across the cut. Blowing air across the cut to blow the flame out has to change when you are processing in one direction, then turning and processing 90 or 180 degrees from the original direction. IF the assist gas is retarding the burn (using inert gas like Nitrogen or compressed air), or enhancing the burn (using oxygen), the amount of gasses involved with the laser process has to change as you change directions or processing. An air assist cone, blowing whatever gas used directly down into the laser process should produce more consistent results throughout a cut path. It should not matter which direction the movement system heads, the air assist gas should be more evenly distributed through the kerf.

I don't know anything about carbon particles causing divergence or convergence of beam. That is not saying that it does or does not happen. I might have just cut my teeth before we new anything about it. Heck, we might not have even had a table of elements back then!:D

[Michael Simpson Virgina]

I can see Rodne's point of view. He is a very practical person. He goes more by personal experience (and he has a lot) than by scientific reasoning.

A while back I designed a control system for my woodworking shops dust collector and posted the instructions on a woodworking site. I had several EE's complain that it would not work or would fail in a very short time. Well here I am 13 years later and its still working.

@Rob
You hit the nail on the head about then nozzle and direction. When I was cutting circuit boards moving in the direction of with the air flow on the nozzle I was getting huge amounts of flame and residue. By reducing the cut direction it all but disappeared. With a Coaxial system I would not think that direction would not have anything to do with it. I can only deduce that in the case of cutting circuit boards the nozzle was the way to go.

@Dave
If you do design a system the ability to go coaxial or nozzle would give you more versatility. As for the air blowing on the optics. I just don't like that concept. Too much can go wrong with that.

[Dan Hintz]

A while back I designed a control system for my woodworking shops dust collector and posted the instructions on a woodworking site. I had several EE's complain that it would not work or would fail in a very short time. Well here I am 13 years later and its still working.
Michael,

Now you've piqued my curiosity... what could you have possibly done with a controller that would have EEs questioning its longevity?

Practicality and theory have to meet somewhere. Imagine my frustration talking with a salesman trying to sell me a $10k extraction unit for my laser. According to him, his engineers insisted I needed a 3-phase motor to get the pull necessary, and this is with (supposedly) direct consultation with ULS engineers to verify cfm requirements. He was none too amused when I explained to him that despite the numbers he was spouting, my $100 Harbor Freight fan was doing a commendable job. Needless to say, he's not getting my business (and especially my money).

So what happened? Did the guy get the numbers wrong? Maybe, but doubtful. The more likely explanation is he simply did not understand what the numbers were telling him. He admitted the ULS guys said the quoted numbers were worst-case scenarios, but even so, his solution was 10-times overkill. All he knew was his spreadsheet and what little experience he had with industrial systems.

[Rodne Gold]

My point , as I have stated in this thread is it is not the air assist that shapes the beam it is the effect it has on optics , mirrors , clean laser path and the cut itself that changes the way the laser works on the material.

I am both practical and scientific and apply both principles. I am also open to any suggestion that does not conform to scientific principles...

For example in audio , there are folk that swear that different digital cables modify sound...no one can explain this scientifically but the fact remains ppl hear differences...
Maybe the measurments currently employed are missing something that is modifying the sound or that ppl are fooling themselves there is a difference..the fact remains that to the person hearing the difference it is a truism.
At any rate , as far as I am concerned , no matter which type of air assist you use ..it's vital to getting good results with a LOT of laser applications and I can't understand why it is not a standard option for the lasers we use.