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A project log for MultiBot CNC v2

A low cost 3D printed CNC that can be built with minimal tools yet is capable of great things.

David TuckerDavid Tucker 05/14/2021 at 01:240 Comments

I just noticed that NEJE.shop has updated there laser diode module page and there are three new modules now available. One is a cheaper 5w version of my 7.5w module model number N40620, interesting but not exiting.  The exiting one is the new A40630 module.  This is the same 7.5w module I have but it adds a collimating lens to the diode. NEJE calls this a FAC or fast axis correction lens, you can see an example of it on this ebay listing. This has the effect of reducing the speed (angle) at which the fast side of the diode diverges, the end result is the spot size of the laser is more or less square and smaller in area.  

According to there specs they are reducing the spot size from 0.08 x 0.06 mm to 0.04 x 0.04mm, that takes us from 0.0048 mm^2 to 0.0016 mm^2, a 3x reduction in spot size!  The collimators must reduce the laser power by some percent but even so we should be getting quite a bit more power out of the laser with this.  And this should restore the engraving potential so one laser can be used for both engraving and cutting without compromising quality.

The newer A40640 15w module also uses this correction lens and claims the same 0.04 mm square spot size.  That combined with double the power output on the laser probably puts this close to 4x more cutting power than my uncorrected module.  A K40 CO2 laser uses a 40 watt laser tube, that is still several times more optical power than the 15w NEJE, but it also has several times larger of a spot size so this may be approaching the cutting power of a $300 CO2 laser.  Keep in mind the CO2 laser uses a very different wavelength (infrared vs blue) and so it can cut some clear materials that the NEJE cant.

The minimum spot size has everything to do with the wavelength of the light we are using.  Our blue lasers have about a 450 nm wavelength (0.00045 mm), while a CO2 laser has a 0.01 mm wavelength.  If we had a square (round) spot in both cases then the blue laser should be able to focus down to a much smaller spot size.  in practice the CO2 laser is probably producing a 0.3 mm square spot size, while my laser diode is producing around a 0.1 mm square spot, and the new modules above claim a 0.04 mm square spot size.  Assuming this is true, then the new module has a 50x smaller cutting area than the CO2 laser!  That sounds too good to be true, but I suspect a 10x improvement is well within reason.  Also keep in mind this is the ideal cutting area, beam divergence can have a big impact on how thick of a material you can cut.

Anyway things are getting exiting for laser diode cutters, they are getting close to being powerful enough to compete against low end CO2 lasers, while being much simpler to operate and maintain (no large glass tube, no need for water cooling).  Exiting times indeed.

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