Maker Pro

K40 Laser Cutter Upgrades

Adventures with a cheap 40W Chinese laser cutter

Ian

Administrator
Aug 23, 2006
1,486
Joined
Aug 23, 2006
Messages
1,486
Ian submitted a new Showcase Item:

K40 Laser Cutter

After much deliberation and questions on the forums, I finally bought a K40 laser cutter. It cost around £350 (after discounts) and was delivered within 2 days from a UK warehouse - which means I can avoid any lengthy delays and import fees from ordering direct from China. Here's the model I went for:

https://www.aliexpress.com/item/UK-...-Engraver-Cutter-woodworking/32810421426.html

I'd like to think I've got quite realistic expectations for this laser cutter, as it barely cost much more than it would be to buy a cheap 40W CO2 laser tube. I know it'll need a lot of tinkering to get the most of it, which is half the fun ;).

It was packaged securely and arrived without a scratch - thankfully the glass laser tube survived the journey:

View attachment 40255

A few accessories were provided, tucked away inside the lid:

View attachment 40256

There was a manual in English, software CD + license dongle, water pump (for liquid cooling), extractor fan and hose. The only other thing that is required is a bucket or similar container, plus some distilled water to circulate through the laser tube.

For some odd reason, the laser cutter comes with castors - but it's clearly designed to be used on a workbench. Before I did anything else, I unscrewed the nuts from within the chassis to remove these.

Before powering the laser cutter up, I gave the machine a once over to check all of the connections. Thankfully, the quality within the main unit seems acceptable - there were a few connections that had bootlace ferrules a little too long (not dangerous, but I gave them a trim and reconnected them). It's cheaply fabricated but seems solid enough. However, I'm a little concerned that there is no laser interlock for the lid, so this is one of the things I'll be changing as soon as possible.

Here's a photo of inside the electronics bay (the loose connection was intentional!):

View attachment 40257

Here's the 40W CO2 laser tube, underneath a cover at the rear of the unit:

View attachment 40258

The laser tube was manufactured only a couple of months ago, so it's comforting to know it wasn't sat on a shelf for a year or two before I used it.

The gantry system within the laser cutter uses basic linear rails to control the X and Y axis, and there's an awfully small clamp build in to the cutting bed. The total cutting area is around 300x200mm, but the clamp can only hold around half of this...

Read more about this showcase item here...
 

KJ6EAD

Aug 13, 2011
1,114
Joined
Aug 13, 2011
Messages
1,114
Casters instead of leveler feet is weird; probably just what they had handy that fit the holes that day. Is there no compressed air system to keep the lens clear?
 

Ian

Administrator
Aug 23, 2006
1,486
Joined
Aug 23, 2006
Messages
1,486
Casters instead of leveler feet is weird; probably just what they had handy that fit the holes that day. Is there no compressed air system to keep the lens clear?

Oddly they market the castors as a selling point, I'm not sure why :confused:.

No air assist on this model either - it's a real bare-bones system. I've got a mini air compressor arriving next week, but I need to measure the barb dimensions once it arrives before I can order in any tubing. I've seen people design 3d printed clips that funnel air down the beam path, but I'm a little concerned that I'll end up with it melting at some point. My current thought is to 3d print a clamp that fits on to the top of the moving platform, with a 4mm copper pipe bent to blow near the focal point.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Joined
Jan 21, 2010
Messages
25,505
Some of the things I would do or consider:
  1. Get an aquarium air pump and use it to direct air over the mirrors. This will keep them clean.
  2. Get some airflow (any at all) through the air-assist connection. It doubles as a coolant for the lens and helps stop dirt getting on the lens (a major cause of lens failure)
  3. MDF is cheap ad cuts easily. However the muck it leaves behind is terrible. If it's your laser cutter and you can decide not to use MDF, you'll be doing yourself a favour.
  4. Honeycomb is great, but hard to clean. Parallel "knife blades" are easier to clean, but stuff falls through them.
  5. Use magnetic reed switches for interlocks and have two in series.
 
  • Like
Reactions: Ian

KJ6EAD

Aug 13, 2011
1,114
Joined
Aug 13, 2011
Messages
1,114
Good. It seems you've got all issues covered even if the manufacturer didn't. I used a honeycomb base and only noticed unfortunately-sized circular cutouts of ABS catching in it occasionally.
 
  • Like
Reactions: Ian

Ian

Administrator
Aug 23, 2006
1,486
Joined
Aug 23, 2006
Messages
1,486
Thanks for the tips!

Get some airflow (any at all) through the air-assist connection. It doubles as a coolant for the lens and helps stop dirt getting on the lens (a major cause of lens failure)

I was going to direct the air-assist via a copper nozzle directed near the cutting point, which should blow most of the smoke away from travelling up in to the focal lens. Here's an example image that describes what I was going to build:

Copper.jpg

However that wouldn't get much air flow hitting the focus lens (contained in the ring underneath the moving platform), it would just keep smoke out of the way. I had't considered your point about the air flow cooling the lens when thinking of this. Do you think it would be beneficial to get a replacement head where the air assist is channelled down the beam path and may cool the lens a little more? A bit like this one:

New Head.jpg
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Joined
Jan 21, 2010
Messages
25,505
I'm struggling to comprehend what they're doing with the lens on this thing. It must be totally unprotected.

Yeah, I would get a head like the one you suggest. Also note that there is air on only one side of the lens. Bleeding some air into the other side will keep the upper side clean. You have one less adjustment too -- the air can only go where the beam does :)

Having said that, just directing a stream of air over the lens in the current configuration would probably work too.

Practically, the worst you'll do is destroy a lens. At 40W, the laser won't do that as fast as a higher powered device.
 
  • Like
Reactions: Ian

skenn_ie

Sep 7, 2009
31
Joined
Sep 7, 2009
Messages
31
I suggest that the hole in the box would be useful, and given that the laser is focused quite close to the nozzle, the power density at desk level would be quite low.
I wonder if a kit is available that would facilitate an existing X-Y table. I have a CNC router which I would like to convert for laser or 3D printing as well as routing.
 
  • Like
Reactions: Ian

Ian

Administrator
Aug 23, 2006
1,486
Joined
Aug 23, 2006
Messages
1,486
I suggest that the hole in the box would be useful, and given that the laser is focused quite close to the nozzle, the power density at desk level would be quite low.
I wonder if a kit is available that would facilitate an existing X-Y table. I have a CNC router which I would like to convert for laser or 3D printing as well as routing.

I can't find the link anymore (still looking), but I saw a post on another forum about a member that burnt the table underneath the laser cutter through that hole :eek:. I imagine it would take some time, but I don't fancy risking it just in case (as there is plenty of ventilation elsewhere). Perhaps overkill, but I don't want to take a chance ;).

If you want to use a laser diode, there are quite a few modules that should be an easy swap - perhaps something like this 5.5W version:

https://www.aliexpress.com/item/Fre...er-cutting-TTL-module-5500mw/32794985652.html

I think it would be limited to engraving (or cutting <3mm laserply/acrylic over many passes), but it should be a straight forward swap if the CNC controller can be configured. I've seen a few people add them to 3D Printer platforms with good results. I'd really like to see the results if you do try converting your CNC router :).
 

bushtech

Sep 13, 2016
1,025
Joined
Sep 13, 2016
Messages
1,025
Nice work Ian! Is the shadowing caused by diffraction of laser by smoke or wood charring?
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Joined
Jan 21, 2010
Messages
25,505
The shadowing looks like smoke to me. Air assist will reduce this a lot.

Simplest best cut sold be at 100% power and with a feedrate as fast as possible so that the material just cuts through.

Let's say that is 100% @ 20mm/s for 3mm ply.

You can get a slightly better cut with 2 passes at 100% power and 40mm/s. This will also cut through a little more deeply.
 

kellys_eye

Jun 25, 2010
4,874
Joined
Jun 25, 2010
Messages
4,874
Would using a directed jet of blown air help the cutting process? i.e. clear the residue/smoke to allow the beam to cut more cleanly?

I've seen many videos of commercial laser cutters and still wonder if they just rely on the laser 'blasting the f**k out of the material' or they actually 'blow' the stuff out of the way like a gas torch does.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Joined
Jan 21, 2010
Messages
25,505
The blast of air (air assist)
  1. blows smoke out of the way so the laser isn't attenuated
  2. Oxidises the material
  3. Cools the lens and protects it from smoke and debris
  4. Cools the workpiece.
Depending on what you're doing, some will be more significant than others. Number 2 is important for metal cutting.
 

bushtech

Sep 13, 2016
1,025
Joined
Sep 13, 2016
Messages
1,025
Agree with kellys_eye. I feel you need to move some serious air. Something like opening the valve on a scuba tank:)
 

Ian

Administrator
Aug 23, 2006
1,486
Joined
Aug 23, 2006
Messages
1,486
I'll see what I can do to improve the airflow - at the moment I'm using an ACO-318 (3600 l/h), but perhaps that isn't enough. Hopefully with some faster cut speeds I'll be able to minimise the scorch marks further.

Next time I do a cut, I'll take a photo of the shadowing - it's separate to the diffuse scorching around the cut lines, it almost looks like the laser cut/engraved at a 2mm offset at 5% power. It doesn't show too well on the photos above, but I'll take a closeup of the issue if it's still there after cleaning the mirrors/lens.

I think I need to buy in some more plywood for testing :D
 

bushtech

Sep 13, 2016
1,025
Joined
Sep 13, 2016
Messages
1,025
Off the wall suggestion: Give the cut areas a light sanding with some very fine sandpaper. Might clean up nicely
 
  • Like
Reactions: Ian

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Joined
Jan 21, 2010
Messages
25,505
I presume you know how to check that the laser is actually hitting the centre of the mirrors and the centre of the lens. If it's hitting the edge of the lens you can end up with coma. And that's the effect that you maybe describing.
 

Ian

Administrator
Aug 23, 2006
1,486
Joined
Aug 23, 2006
Messages
1,486
I presume you know how to check that the laser is actually hitting the centre of the mirrors and the centre of the lens. If it's hitting the edge of the lens you can end up with coma. And that's the effect that you maybe describing.

I aligned them all to be very close to the centre (which was the most time consuming process of the whole thing, as the tube was so out of whack!) - however I wonder if I knocked something when I was fiddling with the air-assist tube. I'll re-check this today and make sure it's still ok :).

edit: On second thought - I don't know if it's hitting the lens centre, only that it hits all of the mirrors centre (at all head positions) and enters the laser head correctly, just before it hits the lens. I'm printing a jig I can temporarily place over the lens holder to ensure that it is hitting it in the middle, just to confirm.
 
Last edited:
Top