Help with Cracked Lens

[Paul Phillips]

Well this sucks, this is the 2nd lens in 3 months that we've broken! The last one was my helper using Acetone to clean it and I'm guessing it was still warm, well I went to use it today and found that he had left the lens caked with residue supposedly from some old Rowmark he was using, so I went to clean it and 1st try only removed a portion of the gunk so I decided to soak it a bit more so put two drops of cleaner on it and about 3 seconds later it cracked, so my question is has anyone had this happen before and if so what should I do to avoid it next time. I suspect that the residue on the lens reacted to the cleaner and contracted causing the lens to crack. I always use the method that Mike McKenzie showed me using the factory lens cleaner and optical cleaning tissues that came with the machine, 1 drop of cleaner on the lens and a very light wipe with the tissue this usually works fine on normal light build-up but for some reason not this time with some heavy build-up so what is the best method for cleaning heavy build-up from plastic residue without cracking the lens? Also, who has the best price on lenses? Last time I went through LaserBits but then I found out they were more than the OG factory lens.
Thanks,
Paul

[Joe Pelonio]

I have heard others with that problem and cannot understand it. I have the original lenses that cam on my machine in 2004, and clean them with photographic lens cleaner and tissues (Kodak) and have never
had a problem, but also have never had a buildup of debris from Rowmark. I only use air assist for cutting, but I have a nice powerful exhaust system. I wonder if yours is too weak or perhaps has a leak and is
losing suction.

[Brian Terry]

check out laserresearch dot net I got a lens off them for my ULS. If I remember right the lens was about $135.00 for 1.5

[Scott Shepherd]

I have heard others with that problem and cannot understand it. I have the original lenses that cam on my machine in 2004, and clean them with photographic lens cleaner and tissues (Kodak) and have never
had a problem, but also have never had a buildup of debris from Rowmark. I only use air assist for cutting, but I have a nice powerful exhaust system. I wonder if yours is too weak or perhaps has a leak and is
losing suction.

That's because your air assist is a "wash", rather than through a nose cone. I have had numerous conversations with several companies and I feel like I'm talking to people that have never run a laser. With nose cone systems, IF you run vector cutting with the nose cone on and air off, it will create a vortex and suck the debris right into the hot lens, melting it to the lens. It's not mentioned anywhere it anyone's manual, that you should NEVER vector cut with the nose cone on and the air off. Tech support will say "We've never heard of that". Well, try it then. I can assure you with 100% certainty, if you vector cut plastic with the nose cone on and the air off, you'll break a mirror if you ignore it long enough (minutes, not hours).

Why this isn't in every manual baffles me, but I guess you'd have to admit there is an issue before you can address it in the manual.

Also, Joe is right, low CFM will cause the smoke debris to go up a little before it goes out. I've seen the mirror and the lens get caked from raster engraving with low CFM.

[Paul Phillips]

Thanks guys,

Steve, my machine actually came with a print out that I keep posted next to it which warns not to run it with nosecone on and no air so I have been practicing that since the beginning.
Joe, I use a 1200cfm vacuum which actually works nicely as a vacuum table for holding down thin sheets so I doubt that's it. It could be that my helper is not being completely honest with me and he forgot to turn the air on which would explain the reason for the residue. I hate having to explain to the boss why we have to replace another lens especially when finances are tight, and that the helper may be the problem.

[Martin Boekers]

You may want to check to make sure that they air is making it through the nosecone and there isn't a crimp or obstruction in the line.

I don't use a nose cone system, I have explained to co-worker about checking the lens daily even more so if they are cutting or burning
stuff that make a lot of dust or smoke. I still find when I check the lens from time to time it's dirty.... I have had "chunks" of stuff fused
to the lens, but most all cleaned up without damage. This doesn't make me happy......

I do see Scott's point if it "sucks" it up the tube while still molten, I can see that it could cause more issues. I have my laser programed that
air assist is automatically turned on in vector mode, is that possible with yours?

[Gary Hair]

I have my laser programed that
air assist is automatically turned on in vector mode, is that possible with yours?

I have that option in my driver, a checkbox for "air assist". It is simply a relay that provides power to a 110 socket on the laser. Since I have a big compressor in the garage that provides air, not a small airbrush type compressor, I had to use a solenoid to turn the air on and off. Works great and I never forget to turn the air on (or off...).

[Joe Hillmann]

How often are you checking your lens?

When I am running the laser heavily I will check the lens every hour or so but only clean it when necessary(sometimes it needs to be cleaned twice a day other times I can go weeks without needing to clean it). Also are you letting the lens cool before putting the cleaner on it?

Of course it it is caused by the nose cone an the air not on then none of what I suggested matters.

[Paul Phillips]

Hi Joe, yes, I make sure the lens is cooled first and I check the lens several times a day depending on usage and I've never seen it caked so badly which brings me back to my helper as the possible culprit. I keep 2 CNC machines running full time as my primary job and supervise the Laser and Rotary Engravers, I use them when I have time but have a trainee that uses them most of the time so I can only go by what he tells me he is doing, he says he is following the procedures I have given but I find I have to sometimes remind him, "hey, you need to clean this, it's dirty", I guess I need to watch him more closely.

[Scott Shepherd]

With that much air flow, it's got to be related to the nose cone on with the air off, in my opinion. I clean my lens about once a month, whether it needs it or not. I cut a fair amount of rowmark and acrylics on it and every time I check it, the lens is clean. Whenever someone else uses it, I always get the "what do I do, leave the nose cone on, the air off, or the air on and the nose cone off?". I even make a sticker that's right next to their head while sitting on the computer that says "AIR ON-NOSE CONE ON, AIR OFF-NOSE CONE OFF". Yet, they still ask almost every time, so my guess is that it's user error.

I only have 850 CFM on that machine and my lens just stays clean.

[Chad Fitzgerald]

ok this has got me wondering, i always have my nose cone on, noone ever mentioned taking it off let alone having it with or without air assist. readin gthe last few posts, im now confused.
What is the proper, or right way when it comes to the nose cone and air assist?? Also curious as to the "why" there is a difference.
thanks chad
sorry for hijacking the thread!!

[Paul Phillips]

Chad, this is what was included in the documentation when I bought my machine. I suspect that what happened was that my helper ran the machine with the nose cone on and the air assist off which caused a heavy build-up of residue on the lens as well as possibly stressing it out so that when I went to clean the residue off, it contracted and caused the already stressed lens to crack.

warning.jpg

[Scott Shepherd]

That's great to see Paul. I can't tell you how many tech's I have spoken to over the years that have told me they have no idea what I'm talking about and there is no issue with running the air off and the nosecone on. Actually, to this day, I've never had anyone in tech support agree with me, so it's nice to see they have it as a warning, but no one knows anything about it.

Paul, stay on your laser operator because when that lens is getting clouded up in the early stages of this happening, the vector cutting will go bad quickly. The kerf will get really fat and it won't burn through. I've actually been able to hear the difference in the cutting and knew something was wrong, so I went over and looked.

[Rodne Gold]

Chad , the GCC spirits don't have an issue with the nosecone and sucking up debris.
I modified my chinese machines tho , stopped air assist going thru the cone and angled a pipe to point at the workpiece where its being lasered , no issues after that.
I use air assist ALL the time , engraving and cutting anything barring stuff it might blow away.

[Chad Fitzgerald]

thanks rodney, good to know. ive never taken out while engraving and sometimes use air sometimes not. never had a problem but thought maybe i was heading towards one.
thanks again.