Added by darrenp over 11 years ago


I'm toying with the idea of getting one of the cheap chinese K40III lasers off ebay, has anyone got any experience of these? I've seen a couple of websites with people mentioning them, but then no news. I know they're very cheap, and you get what you pay for, but for a hobbyist like myself they look like a good price 50-60% cheaper than a 3020. Most of the problems with them seem to be around the electronics, which I will replace rather rapidly with a LAOS board (and document the procedure on here of course!). From the photos I've seen they come with a couple of different motherboards, but the connections to the hardware look fairly straight forward.

Any hints or tips are very welcome. Is there any way to get a cheap HPC without the electronics for a similar price (£600)?



Replies (16)

RE: K40III - Added by hugomeiland over 11 years ago

From the users list, is looks like Darren has bought this setup and has it working!


RE: K40III - Added by darrenp over 11 years ago

Indeed I have. I'm working on documenting it in the wiki now.

RE: K40III - Added by hugomeiland over 11 years ago

That is great! Thanks for spending time on documentation!!

In the materials section I see you are using 100% power; in my experience with the HPC, the best power setting is ~70-80% , above those values the beam starts to become wider and becomes less efficient. Do you get the same results?



RE: K40III - Added by DaveStyles over 11 years ago

I have one that came with a moshiboard that melted.

It worked well till the control board melted. When I get it up and running with my rev4 board,.. I'll join in with the documentation too.



RE: K40III - Added by hugomeiland over 11 years ago

Sounds good, enjoy building the rev4 board, and be aware of the required fix as described here:


RE: K40III - Added by darrenp over 11 years ago

There was no way I could use the moshi software long enough for it to melt! It was barely plugged in enough to let me test the cutter.

If you need any help with the K40-III, just shout. I think most of the things I did to get it working are documented on here in some way, but if you can't find them let me know.

RE: K40III - Added by darrenp over 11 years ago

Oh, hugomeiland: I'll give that a try this weekend. It doesn't seem too bad to be honest. Managed to cut through 6mm ply the other day without too much difficulty. 100% power and 2% speed.

RE: K40III - Added by DeanoC over 11 years ago

My Laos rev 4 is on the way to be built and fitted to a K40III. Managed to use MoshiDraw (mostly as a printer driver using CorelDraw as the actual art package) for some projects but had enough the other day when it just wouldn't cut a perfectly acceptable graphics (it also has a tendency for the steppers to go nuts and bash the case, whenever it is unhappy, not good imho!)

RE: K40III - Added by DaveStyles over 11 years ago

One quick question then.

the flat connector.. where did you get one ? What is it ?

I've built and tested my board, I have yet to put it into the laser, and one of the stumbling blocks is that flat connector ?

RE: K40III - Added by darrenp over 11 years ago

This is what I bought:

Just make sure you get it the right way round. I melted a few tracks swapping it round. I'll try to get a decent picture of it at the weekend to show orientation.


RE: K40III - Added by oyvind81 over 11 years ago

I uploade a picture to the wiki, not that good but it is easy to se the direction. Feel free to edit or change. I used the one from the electronics wiki. Rs partnr 718-8772.


RE: K40III - Added by jcosk8 over 11 years ago

Hi! I have ordered a K40 and will be ordering a rev4 board soon. I don't have much idea of electronics, so I will purchase an already built board, I have seen in your wiki (great job and thanks!) and I understand that it's an easy and straight forward connection, but should I change many things from the pre built board to install it in a K40? Maybe it's too hard if I don't know electronics?
Once I've managed that I will probably ask for more help with the set up ;) and hopefully I can build a working Laos in Madrid, Spain (I think it will be the first!).


RE: K40III - Added by DeanoC over 11 years ago

Currently working on K40III conversion, so far its powered up and passed most tests.
Unlike Darrens machine, ours had a Moshi board and a different PSU setup. Will upload photos etc. when have it fully working.
The moshi board strangely doesn't use a 5V power line, so we've used to 7805 to derive it from the 24V.

The mbed tests fine and voltages appear correct when using the test firmware.

However two things that aren't right.

1) The laser is enabled by default, it toggles off and on using no 4 enable with test firmware, so its just flipped (so is the laser enable LED). Also the laser enable LED is quite weak, not sure that means anything... I did also note that Darrens config.txt has "laser.pwm.min 100" and "laser.pwm.max 0" which might indicate its also backwards on his config?

2) The stepper motors aren't working correctly. To replace the pair of TEA7318Ss each stepper had on the moshi board I've used A4988 blacks ( There is a noticeable change in voltage when stepping using the test firmware and when connected to the motor itself you can hear it doing something but no actual movement occurs. My best guess is that its not in sync properly or the voltage levels aren't correct?

Will get back to probing tomorrow but figured someone here might have a helpful thought or two.


RE: K40III - Added by hugomeiland over 11 years ago

Hi Deano,

Great to hear you are making this progress! Do make sure you have applied this fix to the board:
The low enable led is something we used to see before it was clear there was an issue with the rev4 boards...

It depends on the laser setup how the min/max values should be configured, do make sure to test/measure this on an existing setup before going further...

cheers, Hugo

RE: K40III - Added by DeanoC over 11 years ago

Foo (the name of our laser cutter) has a new working brain!!!

The laos board is working (mostly), we can cut basic shapes and engrave. PWM went in easily and visicut was able to use it with no problem. Just got to splice off a light onto the 24V rail and this first round of upgrades will be ready to go.

The 'mostly' working part comes from a few issues (mostly software), any help would be great.

1) Before we did the PWM mod, I checked the voltage across the power pot/knob to determine gnd/+ etc. and was surprised to see it reading 3.3V on the + side. I didn't measure it before changing over to laos but AFAIK there is no 3.3V in the old system, only the laos MBED generates and uses it. So wheres does it get that value from and why isn't it 5V like everyone else and I assume it was before. The laser does seem less powerful, but its hard to tell until calibrated. The wires come off the main laser PSU board which I haven't changed at all. The laser enable/on is +4.2V which is another odd number. Any ideas? Is 3.3V just a coindence to the MCU voltage and its a droop from 5V or ??

2) The bed size parameters. We've used the settings from other peoples config.txt to get it close to right but its still not scaled correctly, any tips on how to work it out?

3) Visicut engrave isn't straight, a quick test had it with a slant. It might not be the latest version but wondering if this is a known issue or is related to having the bed settings right yet (cutting isn't skewed, just engraving)

4) When homing, sometimes if its already at the home point on the horizontal but not vertical, it bangs violently whilst it moves up the y. Homing from the middle of the bed (for example) is fine.

We've been taking lots of hires photos throughout the build, which were sorting and writing up to give a good guide to how to convert this particular KIII-40 using a Moshisoft V4.1 control board to Laos Rev 4.


RE: K40III - Added by DeanoC over 11 years ago

More testing and experimentation with PWM has some good results!

The analog line when measured again appears to be 12VDC at the laser PSU, leaving the cable off (which due to it being negative = 100% made it full power), produced 18mA of laser current when drawing. With it connected to the LAOS PWM connector with a 1K Ohm resistor in place, gave 9.45VDC at maxim, this still produced 18mA of laser current at 100% PWM dropping to 0V at 0% PWM. Was slightly worried by the higher voltage than the 5V described by other LAOS pwm users, but have no issues and its working well.

In fact it working so well, that a few test cuts in Visicut at 100% and 2% speed was able to cut through 4 pieces of acrylic placed on top of each off (2 3mm boards and 2 2mm boards) in 4 passes (possible 3, but we did 1 for luck). Cut are lovely, and even partially fused them together and the multiple pass accuracy (4 different executions from Visicut) was good.

Before starting today, we upgraded the firmware and Visicut to the latest version in GIT and lines appear straight whereas before there was some distinct skewing. We have had a few dodgy runs, one the motion path just appeared wrong and another I send a file too soon and that caused the firmware to go nuts. So one file at a time for now I think.