Cheap Chinese Lasercutter

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For a while I'd been noticing how cheap lasercutters had become on Ebay. I'd considered putting one on my list of 'things to look at when I next fancied a new toy', but was initially discouraged by some mixed opinions I'd read. My only immediate application would be for making SMD paste stencils, but I'm sure I could find other uses...
Eventually I succumbed to temptation. Amongst the various Ebay sellers selling them, it was obvious by looking at other items they were selling that many (especially the Hong Kong ones) were just box-shifters, also selling all sorts of random stuff. I ended up going for a Chinese supplier with good feedback, who only sold cutters, laser tubes and other related items. Model is Shenhui DC-K40, but the same unit seems to appear under different names. Price was £720 delivered - took about a week by DHL - and they'd declared as 'engraver parts, £50' on the customs forms so only £12 to pay on delivery - result! Packing looked less than optimal - two double-wall cardboard boxes with a 1" layer of polystyrene sheet between them, and more polystyrene sheet inside the inner one. However everything arrived intact, and I just had to remove some foam packing from around the tube.

As expected, documentation (including video on CD supplied) was as appalling as we've come to expect from Chinese suppliers. However I already knew what needed hooking up - water pump and reservoir, ventilation etc. so no big deal.

I was fully expecting to have to spend a lot of time fiddling with optical alignment etc., based on experiences I'd heard of from another user who'd bought a larger model from a UK reseller, however the only thing I had to actually fix was the flex cable, which had come unstuck from the bottom of the case (see pic later).

I tried a quick cut of a polyester solder paste stencil, and it came out pretty well considering the power setting was pretty arbitary - certainly useable and with a bit of tweaking probably capable of cutting for 0.5mm QFPs.

As you'd expect from China, the software is poorly designed and somewhat flaky but just about useable. The biggest annoyance is  not (AFAICS) being able to set a numeric scale factor, and not locking the aspect ratio when scaling.

The original Ebay listing stated it came with NewlyDraw software, which does raster and vector cutting, but it was actually suppled with NewlySeal, which only does raster and is designed for engraving. You can do cutting in raster mode, but it is very slow, and cutting speed only goes down to 1cm/sec, which will just about do 2mm acrylic in one pass at full power. I've contacted the supplier and they are promising to send the NewlyDraw software, although they did say they didn't reccommend it with this model - I wonder if this means the primitive controller and/or hardware isn't up to moving both axes simultaneously (in raster mode, only 1 axis is moving at a time). Will update when I find out.

Safety & quality issues

There are a number of issues, and there's no doubt whatsoever that the product does not comply with all the required standards, or even the ones it  claims to, but that's nothing new.

No cover interlock - you can just lift the lid and stick your hand in the (invisible) beam. Ouch! OK if there had been one I'd have bypassed it, but it means this machine isn't suitable for unskilled users, or where there may be kids or Health and Safety inspectors about.From the Ebay listing : "Built the micro-active switch to enable the machine do not light when canopy is open which enhance security" Er, Nope.
No beam-on indicator, no key lock, no emergency stop button, no laser class sticker. That's at least five  non-compliances with laser product safety standards.

No water flow or temperature cutout to protect the tube. Nothing to turn off the tube if the motors stop, increasing possible fire hazard. 
Mains and LV cabling bundled together. Tube current meter wired in series with tube, so if a ground wire comes off or the ballast resistor goes open circuit, the front panel meter has 20kV on it. Nice!

Neither the water pump nor extrator fan  are CE marked. both come with suspiciously thin mains cable and puny 2-pin flat US style plugs.

Controller uses socketed ICs - really bad idea for a machine that vibrates, especilly with cheap sockets. I had a couple of 'hanging with the beam still on' issues that seem to have gone away after reseating the chips in their sockets.
Standard pitch screws and locknut arrangement on mirror adjusters look like they would be hard work to adjust accurately.
No end-limit switches - set a size too big and it'll send the carriage crashing into the endstop, although motors probably aren't powerful enough to cause damage.

However none of the above were much of a surprise, and the bottom line  is it does actually work, and performance so far is surprisingly good. 
For example it will cut 0.5mm slivers consistently in 1.5mm thick acrylic.  The mechanics look reasonably OK. 

How well it will last, only time will tell... I've seen  lifetimes quoted of 1000 hours for the tube and 25 hours for optics, so as with many things there is a tradeoff between running costs and purchase costs. You can buy a lot of spare tubes and optics for the difference in price between this and the cheapest Epilog!

Conclusions (so far...)

If you want a cheap cutter/engraver  for hobby or non-critical use, and the choice is between this or nothing, I'd say go for it.
Just be aware of the possible need to spend some time tweaking, and adding some safety features if used by unskilled people or when kids are around - this could easily slice a finger off (but at least would probably cauterise it in the process!).
A water flow alarm and temperature monitor would also be a good idea. The water pump is very quiet and you can't tell if it is running even by looking at the pipe without lifiting it out of the water. Even the very cheap looking extractor is reasonably quiet.

However if you're thinking of starting an engraving business, or lasercutting is a critical part of  your business I'd suggest looking at better made products, or at the very least buying two cheap units so you have a backup.

For the money though  it's hard to complain too much, and performance is surprisingly good.

Of course I may have been lucky and YMMV...! 

When searching on ebay, search for laser cutting as well as laser cutter. CO2 Laser (cutter,cutting) -tube is a good search.

There is another possibly newer model, HX-40A, typically £100 more, from fewer sellers,  which appears basically similar but  addresses some of the safety issues, having keyswitch and cover interlock. It also has mains outlets on the rear for the pump and extractor, an internal lamp, the PC connector on the rear instead of the side, and a multiturn dial pot for current adjustment. It looks like it may also have an adjustable-height bed. Here's a video showing installation and maintainance of this model. If  I were starting over, I'd probably go for this model instead.  Update - I think this one probably also doesn't suffer from the lack of speed control - see speed control hack below

Cute ribbon transit-lock..!

Bed has a spring-loaded object holder aimed more at engraving than cutting. For cutting I put a sheet of large-aperture steel mesh over the top. Although working area is nominally A4, the extraction duct (white, at rear) isn't full-width, which may limit materials that can be used further away from it due to smoke.

Flex cable stitting on mains terminal block - nice!

HR end of the tube, HV wire soldered and siliconed.

OC end of tube, with first mirror. Mirror screws are not fine pitch, and locked with nuts so adjustment is likely to be somewhat fiddly.

Flex to carriage stuck down with thin double-sided tape - this had come unstuck.& needed repositioning

Overview of electroinics. Laser PSU in centre, 50K ballast resistor on right.

 Bodge boards or personality modules? on laser PSU. Chip is a UC2825 PWM controller.

Controller board. Very archaic design - Two OTP 8052 series MCUs, there's even some 74LS  TTL on there, the latter suspiciously devoid of a maker mark! Has a 2004 copyright date on the PCB but this design was outdated even then...!

Can't understand why they socketed the ICs - as well as the extra cost, using cheap sockets in a machine that vibrates is asking for poor reliability.

From the Ebay listing : "Adopt Japan imported advanced motherboard and microchip" - if that control board has been anywhere near Japan then  I'm a Chinaman.

PCB is hand-soldered - what a surprise..!

PSU for controller - just a bunch of 78xx regulators. Also links the laser-on signal from controller to laser PSU.

I used an Addis food container as a water reservoir, which has a nice locking lid to reduce risk of spillage. Pump attatched to lid  for easy access.

Chiller unit, built using a small heat exchanger from a car interior heater. I've subsequently reduced the fan size to a quieter 120mm unit as the 6" one pictured was total overkill. 

Flow switch - produces an audible alarm if water flow stops. Switch is This cheap one from Farnell

Update 12 Feb 2011

Many people said that air assist is pretty much essential for cutting, so I bought an air assist nozzle from Here. Quite nicely made, but can be hard to align. I figured out an easy way to do this - by putting a mirror in the beam path, and some well-lit paper on the bed, you can look down the beam path to ensure the nozzle is centred, so the beam doesn't graze the nozzle.

Place the head at the right of the carriage so you're looking along a good length of beam path, find the head aperture in the mirror, then move the nozzle to get a clear circular spot from the paper,  via the lens.

..and don't forget to remove the mirror when testing!

Speed-control hack

I received the NewlyDraw software from China, and after some initial confusion with dongles, it seems to work OK. A proble though is that it does not appear to be able to control cutting speed in vector mode, either via the layers dialog or machine settings. After some searching it appears this may be a limitation of crap firmware in the controller. This is a problem as the cutting speed couldn't be reduced to do deeper cuts in acrylic.

Being a hardware person, I took a hardware approach to this - underclock the controller!

Initial tests were done plugging different crystals and resonators in place of the fitted 20MHz crystal on one of the AT89C52 controllers. This seemed to work OK, and it could now cut 5mm acrylic in one pass if the clock was reduced to 2MHz.
However a problem with this is it also slows down the homing & beam-off movements, and at 2MHz it's annoyingly slow.

  
What was needed was an easily switchable clock source, which didn't glitch the clock, as that would probably crash the MCU. Looking around at what I had on the shelf, I recalled the ATTiny25 has a fast PWM mode, using an internal 64MHz PLL.

With some tweaks to the RC oscillator calibration to get the PLL to 60MHz, it could be made to output 20MHz and lower frequencies. Using part of a PCB I had lying around that had an ATTiny25 footprint on, and a BCD rotary switch, a switchable clock source was quickly hacked together, giving easy front-panel cutting speed reduction.  

The speed can now be changed on teh fly, e.g. fast while it;s homing and moving to the start, then reduced as required for deep cuts.