Project Logs item created by Ian, Mar 24, 2018
Ian submitted a new Showcase Item:
K40 Laser Cutter
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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 .
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.
Some of the things I would do or consider:
Get an aquarium air pump and use it to direct air over the mirrors. This will keep them clean.
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)
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.
Honeycomb is great, but hard to clean. Parallel "knife blades" are easier to clean, but stuff falls through them.
Use magnetic reed switches for interlocks and have two in series.
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.
Thanks for the tips!
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:
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:
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.
Thanks Steve - it sounds like it may be worth getting a new head to save time and money in the long run. I think I'll go for this one (as the nicer blue one above is a lot harder to get hold of in the UK):
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 . 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:
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 .
Ian updated K40 Laser Cutter Upgrades
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Nice work Ian! Is the shadowing caused by diffraction of laser by smoke or wood charring?
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.
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.
The blast of air (air assist)
blows smoke out of the way so the laser isn't attenuated
Oxidises the material
Cools the lens and protects it from smoke and debris
Cools the workpiece.
Depending on what you're doing, some will be more significant than others. Number 2 is important for metal cutting.
Agree with kellys_eye. I feel you need to move some serious air. Something like opening the valve on a scuba tank
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
Off the wall suggestion: Give the cut areas a light sanding with some very fine sandpaper. Might clean up nicely
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.
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