How I bought a 40W laser engraver in China + some theory of CO2 lasers

You may have seen perky clips on YouTube, where a laser machine cheerfully cuts plexiglass in a completely insane way (viewing is recommended without sound). Well, I thought, I need to buy myself such a toy. Moreover, with a 40W laser and black paint, you can draw circuit boards as well :-)



ATTENTION

Do not try to repeat what is written in this article. Working with the lid open is prohibited, the adjustment of mirrors can be done only by qualified personnel. Eye protection is mandatory - otherwise you can easily lose your sight.

Brief theory

A conventional carbon dioxide laser actually contains Helium and Nitrogen, under pressure below atmospheric pressure. Low power lasers (100W and less) are usually “sealed off”, i.e. just a glass tube with a buffer volume of gas, water-cooled, 2 electrodes at the ends of the tube, and 2 mirrors - one translucent (for radiation with a wavelength of 10.6 microns), the other opaque. As it works, CO2 decomposes and the laser loses power. The higher the temperature, the shorter the service life (usually 1000-2000 hours). Power supply of the laser - high voltage source, ~ 15-20 KV, 15-25mA (for 40W tubes).



40W - enough only for cutting plexiglas / plywood. Metals can be cut only with much greater power (1000W and higher), less - if the melt is blown with oxygen (then the iron with carbon also burns, giving additional energy). On the printed circuit board directly cut the track will not work - because Copper well reflects 10.6 µm radiation. But if you cover with a thin layer of paint, then I have seen positive results. What is remarkable, PVC can not be cut, for example. gases emitted during its cutting corrode the lens (and are not entirely useful for humans).

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Actually, many features of CO2 lasers emanate from the wavelength of the emitted light (10.6 µm, “far” infrared light) - very few materials are transparent to such radiation. Best of all passes such a light - zinc selenide, ZnSe, orange solid. Significantly worse (but cheaper) - silicon and germanium. From the exotic - the usual table salt also passes the light of the CO2 laser well, but the lenses from it are too short-lived.



Mirrors - the cheapest is glass or silicon, covered with a layer of copper or gold - as in the photo on the right (at low radiation powers, this is quite enough). On the production, there are water-cooled copper mirrors, and molybdenum - if during cutting steel a drop of molten metal sticks to a molybdenum mirror, you can simply otkovyrnut, wipe it with a cloth and continue to work



The laser beam can be moved by “flying mirrors” - when both the laser and the cutting object are stationary, or for example, there can be one flying mirror + movement of the object. The laser usually does not move, because it is very long (due to the fact that it is difficult to increase the diameter of the output beam above 1 cm - increasing the power is possible only by increasing the length).



Finally, focusing - a lens made of zinc selenide. In high-power lasers, a parabolic mirror can be used, which immediately turns the beam through 90 'and focuses. Of course, both mirrors and lenses can have an antireflection coating (especially in the laser tube resonator).



Due to the fact that the radiation wavelength is very long, 10.6 µm - the diameter of the point to which the laser focuses is limited by the diffraction limit: for a lens with a focal length of 101 mm - the spot diameter cannot be less than 0.2 mm, and for 51 mm - 0.1 mm (for beam diameter 7mm).



Looking ahead, the tube of my laser looks like this:

How I bought an engraver on Aliexpress.com

Seeing what they are selling on the market, I saw that from the fact that it is not quite fatally expensive (<10,000 $), only Chinese labeled engravers with a 40W laser are sold. Naturally, I decided to buy an engraver directly from the manufacturers, without intermediaries. After wandering on aliexpress.com, I found the first seller. After a small correspondence with the discussion of additional parts (I wanted to buy a spare laser tube), the seller offered to transfer him money by bank transfer "to the village of grandfather" and promised to send the engraver immediately after that. I didn’t do this on my own, any purchases must go through the escrow system of the alibaba system, or through Paypal, otherwise there will be no opportunity to dispute the deal if they send something wrong. The seller dashed off the complaint, and in speed he disappeared from the site.



Found the second seller, but this time he has already agreed to escrow. The weight of the parcel exceeded the permissible for mail and EMS 40kg - so they decided to send by EMS in a disassembled form, together with the assembly instructions. Issue price - $ 1288 with delivery. After a couple of weeks, the EMS courier hardly brought the boxes to my home:

We open and collect

Immediately it struck that during transport the protective glass broke. But so far everything looked optimistic. I put it all together, connected the water cooling, and try to check the laser. I press the test button - there is a discharge in the laser, but the dot on the piece of paper is not burned. Strange ... Paper even 0.1W should burn. I open the protective cover, I look around - everything seems to look good. I shake the test - nothing again. Then suddenly I notice that during the test - the hand feels warm. Tin. It turns out that the adjustment of the Y-mirror is knocked down, and the laser beam does not fall into the X-mirror, but is scattered from a circular surface (above — it is circled in red). Then I understand that everything will not go as smoothly as I expected. Well, nothing to do, it is necessary to adjust.

Adjusting the flying mirrors

Quickly found a clever way to adjust - heat-sensitive paper, which is printed checks in stores. The problem is that there are too many adjustment points for the position of the mirror, and the fastening of the Y-mirror is not quite tough, the Chinese in their style are a pancake.



Everything was going well, the beam was getting almost where it needed, and suddenly the next test switch on of the laser on the left side started to smoke. The next paragraph - flew in 0.5 seconds :-) I think - hmm ... I wonder where there could be smoke, there is really nothing like burning ... Hmm ... A person can “filter out” feelings that he does not expect at all, and focuses on something else (in the same way, you can not notice a knife wound in a fight). And then the pain came ...



It turned out that the finger hit the laser beam, well I also tested it at the minimum stable power (about 10W). (The photo is not for the faint of heart, the blood spattered the walls ). 3 a.m. What to do? Call an ambulance? "- Hello, what happened to you? - Aaaa, take me away, I burned my finger through the laser !!!!"



In general, lucky, got into the nail, the power is small, 10.6 µm is well absorbed, and the wound was superficial (that is why CO2 lasers are used in medicine). Healed quickly. After that, I realized that my path to a working engraver is not close. And I sat down to write a claim to the seller on aliexpress.

Showdown with the seller

After a careful study of the product, a list of problems from 9 points was found - differences from what was in the description, monstrous quality problems (the power supply produced only 14 mA, although for a 40W laser you need 24, the cnc controller was different from what was in description, terrible PCB quality, defective ZnSe lens, “burned” fingerprint on one of the mirrors). The depth of the problems can be seen in the pictures: 1 , 2 , 3 , 4 .



It was a real cut. We spent 2 months in dispute at different levels, going back to the beginning of the dispute several times. The seller made a "mistake" - admitted that he sent me a "different model", but it is "better." It was his fatal mistake, after that it was much easier to argue with him. I demanded the correction of the entire list of problems, or offered to return all this good to him at his expense. Of course, while the dispute is going on - the seller cannot take his money.



In the end, the seller agreed to send replacement parts - a normal power supply (as in the description), a new, non-defective ZnSe lens and 3 molybdenum mirrors. But the nerves were spent quite a few.

Video with laser test:

Result and conclusions

In the end, I got a fun set of “make a laser engraver myself” at a price that is not too high. Now I’m doing a Mach3-compatible controller for it, it’s hard to do something other than stamps with the original one (because the Chinese software curve is sharpened for raster engraving, not cutting).



And with the Chinese, you need to keep your eyes open - they do not stop selling marriage, just to earn an extra $ 10 (that is, they can do it qualitatively, but only if they are held by the throat. If you don’t keep it, you will immediately receive the culling) No transactions without Escrow and without the possibility to challenge the quality after delivery.



Comments, questions, additions?