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Chinese "K40" laser

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mgnbuk19/08/2021 16:07:20
1179 forum posts
71 photos

Does anyone on here have one of the Chinese K40 laser cutter / engravers & would be interested in doing a test engraving for me ?

I may have to laser engrave a part number on a graphite component at work & would be interested to see if a 40W laser would be man enough for the job.

There are suggestions that the "40W" lasers are nearer 25 or 30W in reality, but as the sales pitch for (at least some versions of) these machines shows engraving marble they may do what we need without spending a large amount on a full-blown industrial machine.

I would also be interested to know more of real life experiences with these machines - capabilities, accuracy, reliability etc. - from a personl perspective as well as for the work application.

Nigel B.

Robert Atkinson 219/08/2021 17:07:52
1199 forum posts
20 photos

Be aware that these are not professional machines and do not meet safety standards. OK for "at your own risk" hobby work, but not for a business. If somone was injured e.g. blinded at work the company would have no excuse and theier insurance company may not cover them either.

Robert G8RPI.

David Colwill19/08/2021 17:10:48
774 forum posts
40 photos


I have one that is set up and ready to go.

I couldn't say what the true power is but suspect it isn't 40W.

PM me contact details as i do have some graphite and may be able to do a proof of concept.



Tim Stevens19/08/2021 18:48:03
1588 forum posts

A bit of science: The effect of intense heat on marble is quite different from that with graphite. Marble (calcium carbonate) decomposes at red heat into quicklime (powder) and carbon dioxide. Turn off the laser heat and the process stops. Graphite, in the presence of air, burns away, and once hot enough it continues to burn without needing the laser heat. If there is no oxygen, in a vacuum, the graphite will get hot but nothing else happens until a very high temperature is reached. Remember that crucibles for melting brass etc are often made of graphite. But with a powerful laser in vacuo it should be possible to melt graphite. The power is needed because graphite is quite a good conductor of heat, so it might be better to the job in a draught of some non-reactive gas (argon, perhaps nitrogen?) to take the heat (and the molten carbon) away.
My reference says C melts around 3800 centigrade - the highest temperature in a comprehensive list.

This should not stop you trying, as my negligible experience in this area is likely to be as limited as some others, and it would be interesting and useful to find out more.

Regards, Tim


Edited By Tim Stevens on 19/08/2021 18:50:14

Robert Atkinson 219/08/2021 21:12:51
1199 forum posts
20 photos

Graphite does not melt, it sublimes directy to vapour. This is at about 3600 degrees C.
Argon shield gas to keep the lens clear would be enough to stop any chance of igntion, not that it's very likey, Carbon arc rods don't keep buring when you turn the current off.
Nd-Yag lasers are better for marking than CO2 for marking graphite.

Robert G8RPI.

duncan webster20/08/2021 00:09:19
3946 forum posts
63 photos

The windscale fire was burning graphite. Helped by them turning up the wick on the cooling fans in an attempt to blow it out. Only when a hero decided to direct a fire hose into the inferno did they put it out. Probably a matter of scale, I suspect a small piece would self extinguish

I think the guide vanes on V2 rockets were graphite but the hot gas didn't contain oxygen, so they did not burn away

mgnbuk20/08/2021 09:57:40
1179 forum posts
71 photos

Robert: Quite right to point out that a hobby grade machine will not meet industrial standards out of the box & will need additional interlocks / safeguards / rectifications before it could be released to my collegues. My only laser experience was with my previous employer, where I was provided with a Renishaw ML10 laser interferometer to setup & diagnose positioning & alignment issues with CNC machine tools- not really the same animal !

My first port of call for advice on operating equipment I am unfamiliar with is the relevant HSE Guidance, as it will be if this project gains momentum. Given the low initial cost of these units, adding a solenoid released guard interlock unit & a safety relay to operate it to lock out power to the laser tube (& possibly operating a solenoid operated steel shutter to the laser output port) at the same time as addressing the known earthing & power supply issues should not be too difficult - even doubling or tripling the initial cost would still be cost effective compared to a full blown industrial machine that would probably be overkill - always supposing that the Chinese machine is capable of doing the required job ! I would also need to invetsigate whether an air jet would be required & fume ventilation requirements.

Tim: I know that the particular item I would be working with can be laser engraved as our potential customer has provided a sample. Due to commercial confidentiality I can't give any more details, unfortunately. Graphite does burn but requires an external heat source to do so - put a piece into an oxy-propane flame & it can be seen to being slowly consumed, but take it out of the flame & it does not self-sustain. The dust is not explosive, unlike other dusts. We make graphite heating elements for vacuum furnaces that operate at 1500 C that can last for years - but an air or cooling water leak providing oxygen at that temperature & they disappear quite quickly (as does the graphite felt insulation). The sample I have seen showed black/brown smoke staining on the surface at the ends of the engraved numbers that did not easily rub off.

Duncan: The V2 guide vanes were graphite - there are some on display at the Peenemúnde museum. I guess that they didn't need to last too long in that application, rather like the rocket motor nozzles in current missiles - only a couple of seconds burn time & you will not be looking to re-use them..

David: You have incoming mail.

Thanks for the replies.

Nigel B.

Robert Atkinson 220/08/2021 21:42:36
1199 forum posts
20 photos

Hi Nigel,
I've also used the ML10 system. It is low power <5mW and needed no special precautions other than not looking directly into the beam. And it's visible so you can avoid i and have blink reflex. That employer also built various instruments with higher, but still low, power visible lasers up to a couple hundred milliwatts. Those had to have fixed covers and interlocks. When working on them with covers off they had to be in a controlled area with trained operators and safety goggles.
For a muti-watt invisible laser, a stray reflection escaping a gap in a cover can cause permanent damage and you won't even see it.

A side story, at that job I used to do personal work on the premises ( how I miss the prototype machine shop with manual & CNC lathes and mills, surface grinder exc). I was working on flash tube driven Nd-Yad laser from a naval rangefinder. Iwas just working with the flash tube driver and had the cavity blocked and a blank on the output. Unknown to me the production managey wh was also the laser safety officer was in the factory and saw the flash of the tube and when I told him what it was he nearly had a fit! Made me have an eye exam so If I'd done any damage I could not say it was done at work later.
I asked if they were going to pay for an exam evertime I played with that or one of my other lasers (Ar-ion, CO2 etc) at home...... He didn't have an answer for that. I'm careful and have proper goggles for all my high power lasers (often costing me more than the lasers). Not burnt spotson my retinas.

Robert G8RPI.

Martin King 220/08/2021 22:33:44
997 forum posts
446 photos

Hi All,

Sorry to hijack this thread but recently I saw some videos of a hand held laser cleaning portable unit that worked miracles on things like alloy cylinder heads, surface rust on metal, paint and grease on castings etc

It did not abrade or damage the surface in any way and looked to be the answer to all my tool cleaning prayers!

I got onto the company (TLM Laser) and the guy called me back and we decided that it was perfect for my needs the only drawback being it cost £58,000! Power was 50W to 200W depending on the model.

Why are they SO expensive please?

Regards, Martin .... Not ordering one any time soon!

Robert Atkinson 221/08/2021 09:44:34
1199 forum posts
20 photos

Development cost's, precsion optical and mechanical components, lot's of electronics for starters. There is a big difference between making somthin that works as far as an semi-skilled user can tell and may not be reliable. and one that meets proper specifications and maintains performance during use and has to be supported. Also a reptutable supplier will use quality, properly approved safety components. A cheap hobby laser may have none. For example the laser blocking windows look like orange plastic but there are lots of plastics and lots of dyes. To ensure safety you have to use plastic that comes with compliance certification and the plastics maker has to have certification for their materials to support that. This may mean virgin polycarbonate and expensive dyes. A cheap hobby machine will use the cheapest orange plastic they can find and not bother about it's actual performance. This does not just apply to lasers I've seen cheap machine tools with brittle plastic (probably polystyrene) "guards" that broke if you tried to adjust them by holdng the edge. Proper ones are mde from polycarbonate ot thick acrylic.
Also important for relatively small quantity technical equipment is the cost of certification. To properly prove compliance for all the safety aspects costs a huge amount of money. This has to be covered by sale of a small number of machnes.

Robert G8RPI.

SillyOldDuffer21/08/2021 10:22:31
8516 forum posts
1915 photos

For what it's worth, this Australian gent concludes his 40W CO² laser won't touch Graphite. (Youtube Video)

Graphite is the go to material for rocket motors because it has extremely high melting point and heat capacity. You can boil steel in a Graphite crucible.

A wild guess, it's not just about power. CO² lasers work in the infra-red, which may not be the ideal wavelength for Graphite? Another web source describes engraving graphite with a 20 watt q-switched ytterbium fiber laser and 160 mm focal length lens. ytterbium lasers produce higher frequency light.


Robert Atkinson 221/08/2021 10:37:48
1199 forum posts
20 photos

As noted earlier an Nd-YAG laser is preferred to cut / engrave graphite. This is 1.06nm (1064um) wavelength compared to 10.6nm for CO2.. These are both infra-red wavelengths.

Robert G8RPI.

David Colwill21/08/2021 12:25:29
774 forum posts
40 photos

Having done various trials with this i am inclined to agree that it isn't really practical.

My first attempt did mark a piece of graphite and although it wasn't deep it didn't rub off. However the surface of the graphite was cut with a bandsaw and in reality the ridges of the cut were protecting the marking.

Another go with a smoother surface produced a similar marking but this time it was easily rubbed off.

Using slower speed for the engraving didn't make any difference nor did using air assist.


mgnbuk22/08/2021 17:03:06
1179 forum posts
71 photos

Many thanks to all contributors to this thread, particularly David for being so kind as to undertake the testing & Robert.for the insights into the safety aspects of operating powerful laser equipment.

As a result, I will be recommending that my employer contacts industrial laser equipment suppliers for suitable equipment for the job, should he decide to go down the route of in-house component marking if we get the contract.

Nigel B.

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