Strange issue cutting.

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thejuggernaut
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Strange issue cutting.

Post by thejuggernaut »

I have a 120 Watt Reci that I usually run at about 23-23.3 MA at 5mm/s and cut 6mm acrylic great. I infrequently have to readjust a mirror or two, but nothing big. Today I noticed I couldn't get it to cut very well with a 75MM lens. So I got out some masking tape (preferred target material) and started to do a good full alignment. However, as I went along, the beam was hitting square in the middle of each mirror. The gantry is the large 1200mm by 1800mm, but I very very rarely do more than 2' by 4', so that is what I usually do my alignment boundaries at. At all 4 points (X=0 by Y=0, X=0 by Y=2', X=4' by Y=2', X=4' by Y=0), the beam is hitting the center of the 3rd mirror hole with a preciseness about 1.5 times the diameter of the naked beam width. In other words, it is a good alignment and the beam is not being clipped anywhere along the path. However, it will not give a clean cut. I thought maybe the beam was being clipped by the tip, making it create a weird cut finish, but even when I remove the tip completely, it remains. I am kind of at a loss as to what I should even try to adjust at the point. The lens is fairly new with about 8 hours on it, and looks brand new. No artifacts or burning on it. Any suggestions would be appreciated. I need to get some pieces cut out, but can't figure out why it isn't working. I don't think it is the focus distance. I have tried it at several different heights including where I normally leave it, and the best I can get is the photo below. This is 6mm cast acrylic with paper masking. At a loss...please help!

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Tech_Marco
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Re: Strange issue cutting.

Post by Tech_Marco »

How old is the tube?
To cut acrylic, usually you don't want to use too much air and cut it slow to avoid slide in the edge. We usually used 30% power and run it slow at 5mm /s. With slow speed, even a 40W can cut through 25mm acrylic of course the the bottom part won't be straight though.

Check the alignment from the 3rd mirror to the focus lens. Also, check the focus lens condition may be the coating is damaged. Otherwise, the tube may be ready to end its duty.


Marco
thejuggernaut
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Re: Strange issue cutting.

Post by thejuggernaut »

Right now I am running it about 23.0 MA at about 5mm/s. The tube only have about 200 hours on it and I've never run it over 24MA. It's a RECI tube. The water temp never gets above 80 degrees F.

Here is the naked beam about 10 feet from the tube running through 2 mirrors. It is about a 1-2 second burn.

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This is the tape in front of the 3rd mirror. Burning it from all four corners on a 2' x 4' field. It is as fast as I can tap the button to keep it from cutting through 3 layers of tape.

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This is the one I just cut. This is as clean as I can get it, and it didn't cut all the way through the acrylic. You can see how the beam doesn't look perfectly round where the head was moving vertically that it widened. It is acting like it does when the beam is clipping the nozzle, but it still does it when the nozzle is completely missing.

Image
thejuggernaut
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Re: Strange issue cutting.

Post by thejuggernaut »

That is the exact same post....The tube is physically about 2 years old. I use it probably 8-10 hours a month.
thejuggernaut
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Re: Strange issue cutting.

Post by thejuggernaut »

I removed the beam combiner lens and it is cutting through the acrylic now, but it still isn't giving a clean cut. I don't know why it isn't putting out a perfectly round cutting beam. It was fine 2 days ago.
Tech_Marco
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Re: Strange issue cutting.

Post by Tech_Marco »

thejuggernaut wrote:That is the exact same post....The tube is physically about 2 years old. I use it probably 8-10 hours a month.
The beam spot is not good. Check any dirt appear on the surface of the tube. If not, it is time to replace the tube. It is not time/hour used to determine whether the tube is good or not. As time goes by, gas may leak and mirror/lens may be turning bad.


Marco
thejuggernaut
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Re: Strange issue cutting.

Post by thejuggernaut »

I am going to remove the mirrors and see what the bare beam looks like. That sucks they don't last very long. May be better to just get cheaper tubes if they go bad in 18 months to 2 years. Although I don't think it would have gone from cutting clean to an abrupt halt in 2 days. I think there is something wrong in my optics. I'll take a picture tomorrow.
thejuggernaut
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Re: Strange issue cutting.

Post by thejuggernaut »

Here are two burns from the bare beam directly out of the laser tube. It is about 12" from the tube on about a 1 second burst. I am trying to decide if I should try to replace the mirrors first. They both have some trash on them that won't come off, but if you think it is the tube, I will probably just ignore it and keep running it as long as I can till it gives all the way out. I didn't know they just went bad over time like that. I thought they were rated for about 10k hours (which for me is over a decade or two of use) LOL I know the combiner lens was cutting some power because it was very damaged and you could barely see through it.

Image

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Tech_Marco
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Re: Strange issue cutting.

Post by Tech_Marco »

The burn spot seems better without the mirrors. But is not in round shape. Anyway, use it without beam combiner until it is totally not able to cut. It shouldn't last more than two weeks, I guess

Marco
tansh
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Re: Strange issue cutting.

Post by tansh »

How about the beam spot after your 75mm focus lens? Is it a perfectly fine and round spot burn?
daniel.macke
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Re: Strange issue cutting.

Post by daniel.macke »

Hello,
Just after running the laser for a few minutes, can you find something getting hot : mirrors, Mirror mounts, laser head, laser tip?
Heat indicates that some laser power is being absorbed.
If a Mirror is getting hot, it may be dirty or bad : one time I found my second Mirror was dirty and I tried to clean it with isopropyl alcohol. I was quite happy with the result as the Mirror surface seemed to be perfectly clean and free of scratches. But when I turned the laser on, I had lost a lot of cutting power... And the Mirror was getting very hot after a few seconds even at low power! I think the coating of this Mirror just went off , and everything was solved by replacing the Mirror.
Regards.
Daniel
thejuggernaut
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Re: Strange issue cutting.

Post by thejuggernaut »

Well the tube has finally gone out and I have to get a new one now. I typically run it at about 23 ma and it has lasted me about 3 years. I might run it 5 hours a week, so it doesn't get allot of usage. The next tube will probably go bad from age before actual use, so I don't need a 10,000 hour tube. What would you all recommend in the 80 to 100 watt range, or more appropriately, running about 23-24 ma.
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