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NUBM44 CNC cutting normal/half-way acrylic mirror

UnPlug

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Hello everyone! :)
I have a big project in mind and I am pretty sure you guys can help me.... Please help me...

I come to you with many questions, and many of them seem to have been asked in the past but I could not find any good answer for my problem.

I would like to make my own CNC Cutter/Engraver of 100cmx100cm working area, yeah it's huge but I need it like that to cut acrylic mirror and one/two way acrylic mirror.
It should be possible because on the back of the mirror side there is just a coat which makes it possible to cut, also I hope that the one/two way acrylic mirror will be cuttable/engravable because there is approximately 70%reflectivity 30%transmittance and also the acrylic is always a little bit black or silver tinted which should make it absorb light right?
I've read somewhere that for the plain acrylic mirror it should not be an issue but I am still not sure for the half way mirror as the 2 sides are reflecting/transmitting light...

Is it safe to try cutting the half way mirror if some of the laser's light is reflected back to itself?

I will cut mainly 1mm or worse case 3mm acrylic so I should be good right?

For the diode... Because I think I will need high power for my acrylic cutting(engraving the half way mirror) I plan to opt for the NUBM44, but after reading on the forum there seem to be a important problem about the beam size and so the efficiency /power...

I haven't read the entire thread about this laser yet, only the first pages and the last ones, but is there any conclusion about its beam? Is it possible to make it small enough for cutting and sorta get a round shaped beam at very small distances? I know I will have to read the entire thread but I don't have access to a computer yet, I'm struggling with my phone right now...

I don't know if anyone reporting on this has tried to focus on a small distance? Should the CNC laser be close to the cutting material right? It should make the beam tighter and hence more feasible right?

I've read a lot about the G2 lens, 3 elements, G7,Jtech etc but which one should be better for close cutting/engraving? 3 elements if I want my cut and engraving to be precise right?

BTW I thought about the CNC structure whithout their Chinese laser, do you have any recommendations or anything to say about this? 1000mw Mini desktop DIY Laser engraving engraver cutting machine Laser Etcher CNC print image of 100*100cm big working area -in Wood Router from Home Improvement on Aliexpress.com | Alibaba Group


I thought about buying the DTR 25mm copper body for the NUBM44 but is this enough of a heat sink for long lasting cutting / engraving?

I don't have any prior experience with high powered laser nor with CNC building but I've used many and I go on the laser forum for a while now so I sorta get to understand the basics.

Any help would be much appreciated :)

Thank you for reading, have a great day, peace
 

UnPlug

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Wow, not even one answer...
Did I say something wrong...?
I just would like to know if it's possible to get a very fine beam with the NUBM44 by focusing at the smallest point possible? And if so could you indicate me the which lenses I should use please..?
When I look online I see different answers every time, will a G2 lens be enough ?

What about the Heatsinks? Long run time problems?

Thank you ...
 

Alaskan

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Wow, I have a hard time believing you wrote that long post with a phone. Google search turned this up, some answers to your questions here: Diodes for cutting

You can also study this: https://jtechphotonics.com/?p=1648

I don't know if this diode can be focused to a fine enough point you probably want for cutting acrylic, but you can ask this guy how his project went. There is no one here I know of doing CNC laser cutting of materials with a NUBM44 diode, so you might be asking the wrong folk. This is the guy to ask:



I don't see how a mirrored surface makes a difference if turning it over and cutting from the non-reflective side, or painting it with something non-reflective. More here: http://forums.reprap.org/read.php?133,759190

We have a fairly dedicated (sick) help me troll creating a few accounts here right now and possibly hacking old ones too, so you will have to excuse us if we don't jump in to help, but for CNC cutting of materials I think you would be better going to the forum I have linked to in my first sentence of this response, above.

More here on the NUBM44: http://forums.reprap.org/read.php?133,773279 - Not the best choice for cutting due to the large size of the emitter, focusing down to the smal high power density spot you probably need isn't going to happen with this diode, poor choice for many applications. Depends on what you are doing, go check out that youtube video and message the guy who put it up, maybe it can work for you.
 
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CurtisOliver

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I'll try to answer as much as I can.
Personally I don't suggest cutting acrylic mirror with the reflective side facing the laser. If the material is visibly reflective, then it will reflect the visible wavelengths of the laser involved. This could cause unnecessary thermal stress on the diode and diode window. Depending on the material of the reflective film (for example, not aluminium), it may be possible to cut it reflective side up with a co2 laser. This is because what is reflective to visible light isn't necessarily reflective to IR (10640nm). Also from a material processing point of view, if a material reflects the beam, then not much of the beam is actually being absorbed to heat the material up. This pretty much renders the pass useless and instead could damage your laser diode. Most laser cutting done of materials is inferred that you are using a co2 laser and not a visible diode you should note.

Also whilst the NUBM44 is undoubtedly the most powerful diode on offer. It's beam specs are terrible. You can't focus an NUBM44 down to a nice spot like you can an 405nm single-mode BDR-209 or even 445nm multimode M140. It is possible to use them for laser cutting, but expect some loss in power density compared to what you are probably expecting. You also won't get a nice round beam profile from a multimode. Only single modes can give you that nice guassian profile.



As lenses go, the 3-element is known to produce the better looking spots whilst sacrificing some power. The opposite is the G2 which allows more power output whilst lacking the neater spot. The G7 is believed to act almost like the middle lens in some cases. Better spot = better power density but less power going in or More power = poorer power density with more power going in.

You stated about keeping the laser close to the material. How close? Now again with co2 lasers you find that the focal lengths of the lens is quite small. Usually 1/2" from experience. This is due to a little bit of laser physics.
As you may or may not be aware, lasers do not focus to infinity and spread back out again like this >< but instead it looks more like this:



There are two factors to consider when using a focused laser beam to process materials. The first is the beam waist. (The size of the 'dot'.) The smaller the dot, the higher the power density. Now the beam waist is in proportion to the focal length, the input beam waist and the wavelength. If you use a smaller focal length lens the beam waist gets tighter. But this is where the second factor comes in and is most commonly referred to as 'focus/focal depth'. (b on the above diagram)
This is is the area of the beam where the power lies up to at least half the total intensity. In simple terms, the part that cuts. As you reduce the focal length the focal depth also decreases, meaning that the laser starts to lose the ability to cut at depths. But for your purposes, it also makes it harder for the laser to stay in focus over the whole length of the cut. You plan to have a 1m cut bed so you would have to have a sturdy travel beam to prevent warping.

Luckily for you, you plan to use a visible (shorter) wavelength diode allowing you to increase the focal length and focal depth but also maintain a high power density. Co2 lasers have to have a shorter focal length otherwise they wouldn't have a small enough spot size to cut despite their higher output power.
Whereas visible lasers are able to be focused tighter naturally due to their smaller wavelength.

If I think of more, or you have any questions I'll will update with some more for you.

I hope this helps you get a better understanding so you can make a better judgement on what diode to use and what sacrifices you are going to have to make.
 
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Alaskan

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Great response, nice description and beam mode comparison graphic.
 

Alaskan

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If anyone can optically tame the NUBM44, Optlasers can. I am sure that is a good product, just check the cutting specs for your material.
 




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