Diodes for cutting wood?

I'm planning to build a laser cutter, but I'm having trouble finding guidelines on how much power/power density is needed to cut various materials. I know this is going to vary significantly, but I figure there's probably some ballpark information out there. I've got some high power diodes from other projects, an M140 and NDB7875 (the older one, not the better 7A75), and decent enough optics.

The most ambitious goal for the laser cutter is ultimately to be able to cut wood thick enough to experiment with new frame designs for the RepRap, which I'm pretty certain my diodes aren't powerful enough for. Did some crude tests with the NDB7875, and it did a great job at cutting balsa wood a couple mm thick, but I think that's probably the best it's ever going to do without throwing a beam expander at it. I'm not opposed to upgrading the optics, but I'd rather put my money toward a better laser than trying to mitigate the problems that arise from using the wrong tool for the job.

To that end, I'm looking at building a ~40W CO2 laser, but want to make sure I've exhausted all my options with laser diodes first. I pinged DTR about maybe using one of the new NUB44M diodes, but he was of the opinion that the beam quality was poor enough compared to the M140/NDB7*75 that it would be a net loss of cutting potential despite the significantly higher output power. Normally I'd just put together the diode based cutter and test it out since I already have the diodes, but my backlog of projects is long enough already, so on this one I'd like to see if I can just go with the conventional wisdom.

So what say you, fellow laser hackers? Try the diodes and hope for the best, or suck it up and build the CO2 laser?

[Edit] I'm not opposed to building a solid state laser. I've been eyeing laser rods on eBay for a couple years now, and there are some particularly attractive Nd:Glass rods up right now...

Edited 1 time(s). Last edit at 02/26/2016 05:55PM by OutputCoupler.

... my thest show that the actually best single-diode solution for cutting wood is the 3.5W-diode - here the energy density and power is enough to cut 4mm plywood with 4 passes.

I'll estimate, for cutting in a single pass with 445nm you'll need roughly 10 Watts on a spot of 0.1mm - so either two combined 6W-diodes, 4 of the 3.5W-types, or a CO2-laser with >20Watts on a spot of 0.2mm ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Can you get a 0.1mm spot out of the 6W diodes? DTR suggested that they had poor beam characteristics for laser cutting.

I haven't looked into it, but I'm assuming the 3.5W diodes (NUB7A75? Pretty sure my 7875 tops out around 3W, don't have an LPM to check) are unpolarized, so using a PBS cube wouldn't work for combining beams. Can you get good results with a knife edge array, or does that screw the beam quality up too much? You suggested four diodes, so it would seem that a knife edge array isn't out of the question.

That said, four passes doesn't sound too bad, especially given the vastly lower cost of a diode versus gas or solid state lasers. I'm not very concerned with charring, so long as it gives me an accurate hole and doesn't set the wood on fire, I'm happy. Faster is better, but I'm not going to be cutting enough wood to justify an upgrade just for the speed increase.

I have been down that road and decided a chinese laser cutter with a half bad CO2 tube is still cheaper than a really decent and powerful diode laser.
You get an enclosure, exchaust and all the mechanical part, which are not that bad either if you know your tools.
I paid under 500$ AU for a CO2 cutter, Arduino Mega, Ramps and display controller.
Now happily doing Vector cuts, raster works and true 8bit engravings.
If I have to I can cut 3mm plywood in a single pass but prefer 3 passes at higher speeds to get really clean cut.
Solid wood is much easier to cut as I noticed and 6mm hardwood can be cut with air assist in a single pass.
With the now working 8bit engraving it is also quite possible to create "pass holes" that won't go through the material, resulting in much nicer box designs - but have to experiment with this when I find enough time.
Still have not used the SD once and the display right now only serves to display status info as it easier to run through Printrun.
But full standalone operation is possible, with a WiFi enabled SD even through the network


IMHO diode lasers are really great for engraving jobs but not soo good for actual cutting jobs.
By the time you have added decent optics, a good driver and laser module you often reached the price for a complete CO2 machine...
Size is also a matter when you want make printer parts or new frames for your machine, just more fun to be able to go big here
And adding a diode laser to my printer was not an option as I have no enclosure and did not like the idea of harmful fumes all around me.

I would spend my money on a diode cutter with air assist for unfrequently wood cutting jobs.

... you can receive a spot of 0.1mm diameter from a 6W-diode too, if you use a lens with big diameter and short focal length - e.g. 20mm diameter and 15mm FL.

I'm combinig diodes with special GRIN- and fiber-optics, but this is mostly for 'closed' projects, so can't give infos here, sorry ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

The tinkerer inside me won out, and I ordered a NUBM44 to test the relative cutting power versus the M140 and NDB7875. I ordered a couple of DTR's projector optics kits, should be able to cobble together a half decent beam expander. There's an 18mm lens with a 13mm focal length that looks decent for getting a nice, small spot. Have some knife edge arrays handy, but I'm not sure if I'm going to bother with them.

Going to be a little while before I can get around to doing the tests, unfortunately, but I figure between the three diodes I've got something I can make work.

Quote
VDX
... my thest show that the actually best single-diode solution for cutting wood is the 3.5W-diode - here the energy density and power is enough to cut 4mm plywood with 4 passes.

I'll estimate, for cutting in a single pass with 445nm you'll need roughly 10 Watts on a spot of 0.1mm - so either two combined 6W-diodes, 4 of the 3.5W-types, or a CO2-laser with >20Watts on a spot of 0.2mm ...

What cutting speed would you suggest to cut 4mm in 4 passes with a 3.5W diode?

... for "deep" and slow cutting I'm using speeds of 8mm/s down to 2mm/s, for engraving roughly 20mm/s up to 100mm/s.

This depends highly on the material and "fuming rates" ... and adjusting this too with pulse-lengths - shorter pulses (down to 10 Microseconds length) reduce fuming, but won't cut in depth ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Any updates on the NUBM44 ?

I see several references in this thread to the "3.5 watt diode". Which one is it specifically that everyone one likes? I see two on DTR's site, a 450nm and a 455nm (NUBM05 and NUMB06).

From what I (think) I read, the 455nm has better energy transfer to materials. However, I can't tell from what I have seen if there is any beam shape / focus characteristics differences between the two. Also, any thoughts on lenses?

I currently have a NUBM44 and I don't think it's ideally suited for this type of work.

... I'm using the 448nm type from Lasertack - [lasertack.com]

It's specified with wavelength variations from 440nm to 455nm ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

FWIW

1.75 watt 455nm diode laser
cutting cardboard

[www.youtube.com]

Black Depron meat container (doesn't do anything to white depron)

[www.youtube.com]

blue gears allow focus without burning fingers

Thanks Viktor, never seen those diodes before. They look great! $350 bucks is a bit out of my price range for this project, but I've bookmarked the site. Really interested in the lens correction!

Cozmicray, thanks. These days I can never get enough videos of watching people cut stuff with lasers!

if you want to cut a wood or plywood, you'd better need 5.6W or 8W diode laser
to cut 3-5 mm (1/10-1/5'') you would need approx 20-30 passes to cut.

Endurance lasers are reliable and you would need to stop like Chinese that do not work continiuosly...

I do not know why but most Ali lasers do not last more than 1-3 month...
bad power circuit.

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