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2500 mw Laser Engraver - G2 Focal distance

pedwards2932

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I have a EleksMaker Laser A3 2.5 watt laser engraver that I use for cutting balsa and occasionally 3mm plywood. I got an after market glass lens that works pretty good....can cut 3/32 balsa easily and 3mm plywood in 5 passes at 100mm/min. A while back I purchased a G2 lens and I realize it has to focus distance between the laser and lens but I am interested in what the optimal distance to the target for cutting flat material? I would like to compare the cutting capability between the G2 and my old lens.
 



steve001

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I have a EleksMaker Laser A3 2.5 watt laser engraver that I use for cutting balsa and occasionally 3mm plywood. I got an after market glass lens that works pretty good....can cut 3/32 balsa easily and 3mm plywood in 5 passes at 100mm/min.

A while back I purchased a G2 lens and I realize it has to focus distance between the laser and lens but I am interested in what the optimal distance to the target for cutting flat material?


I would like to compare the cutting capability between the G2 and my old lens.
Grammatically your sentence structure needs improvement because it's difficult to know what question(s) you're asking. I can infer though you want to know two things. The focal length of the G2 lens? And: What distance if attached to this engraver the working distance will be? If that's what you want to know, look up how to determine the focal length of a positive lens. Doing that will give you answers.
 

pedwards2932

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I guess I wasn't clear. The specs on the lens gives a focal length which is:
AixiZ G-2 Collimator
Working Distance: 2.357mm (C/G Inclusion)
Effective Focal Length: 4.02mm
I am assuming the 2.357 is the distance from lens to laser? With the lens I have now the distance from the end of lens to the material I am cutting is about 120-140 mm. I had heard that the distance between material and lens with the G2 is different. Someone that had posted on Amazon had said distance to material being cut was 2mm which seemed too close to me. On another forum I am on they thought it was 30/40 mm. I just thought there would be a suggested/optimal distance. From my measuring the 30 mm seemed closer to correct.
 

steve001

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I guess I wasn't clear. The specs on the lens gives a focal length which is:
AixiZ G-2 Collimator
Working Distance: 2.357mm (C/G Inclusion)
Effective Focal Length: 4.02mm
I am assuming the 2.357 is the distance from lens to laser? With the lens I have now the distance from the end of lens to the material I am cutting is about 120-140 mm. I had heard that the distance between material and lens with the G2 is different. Someone that had posted on Amazon had said distance to material being cut was 2mm which seemed too close to me. On another forum I am on they thought it was 30/40 mm. I just thought there would be a suggested/optimal distance. From my measuring the 30 mm seemed closer to correct.
Knowing the focal length of this lens tells me any surface needs to be 4.02mm distant. Taking the experience of others that have burned stuff too closely and damaged the optics tells me that lens is not appropriate if it is exposed. I know nothing about optical setups of engravers. What I do know is this: allowing the beam to expand and using a longer focal length lens allows for a smaller spot size at the focal point. Long ago like 20 years there was a demonstration of a 5mW laser burning wood by expanding the beam then focusing the beam and placing an object at the focal point. I would think having distance from the engraver and the work surface would be a good idea.
 
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Gadget

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You've got everything pretty well right. As for the working distance, you can pretty much make it whatever fits your machine since you can focus the beam. Keep in mind, though, the farther the emitter is from the workpiece, the longer it will take to heat and burn the spot. Just get it as close as you can mechanically speaking, then focus it and go.

-G
 

paul1598419

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You might want to add a blower to remove smoke and debris from the area being cut so it won't get deposited on the lens. This is especially true if you are working close to the surface of the material being cut.
 

pedwards2932

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I am using an aquarium pump with a small aluminum tube aimed at where the laser hits the material to blow away soot and smoke. I can also hook it up to an airbrush pump if I need more air. I think what I will try is different elevations on the material with it focused and set my material on an incline to see where it starts cutting and where it stops. 4mm seems close but with the balsa you really want as fine a kerf as possible.
 

steve001

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I am using an aquarium pump with a small aluminum tube aimed at where the laser hits the material to blow away soot and smoke. I can also hook it up to an airbrush pump if I need more air. I think what I will try is different elevations on the material with it focused and set my material on an incline to see where it starts cutting and where it stops. 4mm seems close but with the balsa you really want as fine a kerf as possible.
You reminded me of something I read long ago . When expanding the beam then focusing it a smaller spot size can be achieved. Whether that's practical for this engraver I don't know. Numerical aperture is important too. That's the ability of a lens to gather light to resolve fine detail or create a small spot. The higher the better.
 
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pedwards2932

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The numerical aperture is .5 for the G2 that I have.

I have a hard time with focusing precisely visually so what I do is stack index cards to the exact height of what I am going to cut then I run focus lines adjusting a little each time until I get the finest line possible. This seems to work and then I use the fastest speed that will cut thru the balsa. Plywood is a little different because it takes several passes. So I don't use a lot of the science behind how the lens works....that is why I am here....trying to learn more. I am hoping to improve the cutting with the G2....faster cutting and less char. I really appreciate all the information and help.
 

steve001

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The numerical aperture is .5 for the G2 that I have.

I have a hard time with focusing precisely visually so what I do is stack index cards to the exact height of what I am going to cut then I run focus lines adjusting a little each time until I get the finest line possible. This seems to work and then I use the fastest speed that will cut thru the balsa. Plywood is a little different because it takes several passes. So I don't use a lot of the science behind how the lens works....that is why I am here....trying to learn more. I am hoping to improve the cutting with the G2....faster cutting and less char. I really appreciate all the information and help.
Check with Edmund Optics lots of information. They carry a wide range of off the shelf AR coated lenses. They might have something with a higher N.A.
Btw, short wavelength light is hard for everyone to visually focus.
 
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paul1598419

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If you have safety goggles, you can often see the spot as a fluorescence, as opposed to the illuminated spot. That should help you focus your laser better.
 

Encap

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If you have safety goggles, you can often see the spot as a fluorescence, as opposed to the illuminated spot. That should help you focus your laser better.
Good point.

I have a hard time with focusing precisely visually so.
Very important---If you don't have laser safety goggles/glasses get a pair if you hope to avoid eye damage
 
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pedwards2932

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I have a pair of these: OD5+ 190-540nm&800-1700nm Laser Protective Goggles Glasses CE Eaglepair EP-1-9 . It is still hard to see the best focus but with the index cards I have imperical proof in that the line gets thinner and starts cutting thru more than one card. Then at that setting I play with the speed to make sure it cuts thru the balsa usually about 350mm/minute.
 

paul1598419

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Seeing the fluorescent spot with a pair of red safety goggles is one way to see the not illuminated spot and focus the beam to its smallest diameter. If you can't do that for some reason, I guess you'll have to use trial and error to find it the best you can. Being able to see the spot is the preferred way to focus a laser.
 

pedwards2932

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I'll try that.....I had to use plumbers tape to tighten the lens thread so it doesn't jump around as you adjust. It is not the easiest thing to do with it set up on the machine. I try to focus at lower than 100% closer to 30% power because it burns thru what I am focusing and hard to see when it burns. I just remember it being hard to tell the smallest dot but the burn lines are easy to discern the thinnest line.
 

paul1598419

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You can use something that won't burn to adjust it. Black ceramic or metal comes to mind. And as black absorbs most of the light, it won't have as much illumination either. But, it needs to be something that won't burn. Also, if you add a spring before you put the lens on, it won't jump around when you adjust it.
 
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