Variable laser power

[Blueyonder]

Hello, first time on this forum so please correct me if I do anything wrong. I currently have a chinese laser running LaserDRAW and I'm verry happy with it but while LaserDraw does what it says on the tin it is limited in function so replacing the current controller with a Pokey card and running Auggie is verry apealing. One issue i have with my current setup is that if I set the laser power to the minimum required to cut material when the head is in minX,minY position, i.e. shortest laser path, this same laser power setting is not sufficient to cut the same material when the head is in the maxX,maxY position, i.e. longest laser path. For this reason i have to set laser power higher to the worse case setting. Is it or will it be an option in Auggie to dynamically increase lasor power in proportion to the length of the lasor beam path or is more of a problem with my setup and not general to all Co2 lasors?

[ArtF]

Hi:

    It will probably be possible to correct for that, but I think you may have an aiming problem
because your trouble should be reversed. A CO2 laser needs distance for its beam to expand,
the longer the better, when it hits the longest path, the beam has expanded the most, and the
lens will be that much more efficient. Its more normal to have less power in the short distance path
from what I understand. I use a beam expander in fact to widen my beam due to a very short path.

    Have you carefully tested your entry to the mirror at both extremes? Is it centered at both ends,
or perhaps more out of center at the long distance end? Since many laser suffer from the distance
problem I will probably add a linear corrector for the distance effect, cant say when exactly. (Though
I would have though Id need to reduce power a touch at the long end..

    Im currently adding DXF import for cutting vectors , so the next release will have more for the user
to select from for a burn or cut operation.  We dont know much yet about how CO2 laser high voltage
supplies work under Auggie, hopefull we'll know more over time. From what Ive read they should
be quite adapatable to Auggie and give as good a control or better than the cheaper co2 dsp driven
units .. time will tell. :)

Art

[Blueyonder]

Thanks Art, Very interesting. I'll spend some time re-checking the beam geometry.

[Joakim]

Hi.

I have a 40W Chinese CO2 laser (the cheap ones). Alignment of laser beam helps, but it still have less power in the far end (longest light travel). Only laser glass tube, mirrors and lens (no beam expanding).

(Not converted to Auggie yet...)

[ArtF]

  Hi:

        How much less power? It woudl be interesting to gather how everyone finds their lasers, how
much power it seems to take to cut what material , and any strangeness you find.

  Generally, from what Ive read, its recommended to have 6' of laser travel, but of course, most of us have
no such thing. I do use an expander on one, but not on the other. My chinese laser isn't the cheap one, but its not
far different either. It could be normal for that effect to happen, just seemed strange.. Rounded part of the
lens is facing upwards, right? ( Believe it or not Ive seen it work upside down.. just not as well. ).

  Mine i supposed to be a 50 watt in the shop, it takes 100% power at about 6mm/sec to cut 4mm acrylic
in one pass, Ive heard  of both better and worse from 50 watts. ( Personally, I suspect mine is really about
40 watts ). My inside laser on Auggie is rated 10, and I suspect is running 15 or so..
(Synrad 10 watts usually give up to 30 at best)

    Power differences may be geometry, or perhaps its normal depending on the laser.. but I cant see a laser losing
power over such a short distance for just reasons of distance.. provided the beam doent get too large.

Another interesting question, how large is the dot as it enters the final mirror port? Any different far or close?

    I do think we can make a correction calibration for it at any rate. My plan is to make things similar to the
delay calibration in the video,the type of calibrations where you select numbers that look best after burning
a test. So far, its all working good, next phase is vector cutting work... Im deep into its code already..

Art

[Joakim]

Hi.

My laser is half disassembled at present... I would like to take measurements when it's running with PoKeys+Auggie.
May be weeks as other projects has to be finished first.

[ArtF]

Hi:

    No problem, and no rush. Nice to know projects are in the works.., when your ready Auggie
will be that much further along..

      Im in a slower portion of code at the moment anyway so updates will be slow over
the next couple weeks as I implement a kind of mini-cam system into Auggie for creating
libraries of commonly used shapes. I find with my laser I tend to cut multiple copies over time
of the same shapes for various projects, but I may want differing sizes and such, so the library
is my attempt to make a scale-able object list for rapid recall and burning at various scales and
angles. Im trying to add Gcode as an input to that as well, so that one can modify Gcode files or
just copy bit of them for future use.. ( grab a single roadrunner and store it as an
object for example..)

  Then Ill begin vector calibration type of work to see how well we can control things for
even cuts across the workspace.. ( that is still an issue on my workshop one at times, but
Im convinced a calibration could cure it.. )..

  It will be interesting when some of you power up with the high voltage units, Im curious
how they respond to PWM control and what kind of tolerance we'll have to adjust things..

Yell when you get to your project.. :)

Art

[Blueyonder]

Art, I tend to leave the laser power the same and compensate by adjusting the speed. As a general observation, If I need to cut at the longest beam length I have to reduce the speed to approx 60% of the speed I would use if I only needed to cut at the shortest beam length. My bed is 300mm x 200mm.

[Blueyonder]

For added info. My Chinese laser (and it is one of the cheap ones) is supposed to be rated at 40W. I have no way of knowing how accurate this is. It's analogue meter reads from 0 - 15mA. I find it takes 1.5mA to fire the laser. I don't really know if its best to use high laser power and fast speeds or low power and slow speed in order to prolong the life of the tube but I tend to use low power and set slow speeds. For 4mm Acrylic (at longest beam length) I can cut fine using 2.5mA @ 4mm/S. The thickest material I've cut is 6mm MDF using 5mA @ 2.5mm/S.

[ArtF]

Hi:

  Well, for CO2 lasers, keeping them below 95% current is recommended to prolong their life.
You should be safe using 12ma most of the time. I tend to use near 100% most of the time. I
dont have an ma meter, but mine wont fire below 27%, and fires up to 100%. Keeping mine
at 95% woudl probably be smarter. But yours sounds way low at 2.5, Id go crazy and bump to
10ma if the manual says you can max at 15ma. ( which is typical). On the other hand, your getting
pretty good results for only 5ma.. 6mm mdf isnt easy to cut. Is that a short focal lens?

  I suspect your cutting way too low a power for most things, bump your speed up and bump power 90% of max
and I suspect youll find it better.

Good info ,
Thx

Art

[Blueyonder]

It's just the lens that came with the laser. The only things I've done is to add a DIY air assist using an air brush compressor that seems to work really well and realign the optics (which may need revisiting if this is the source of the discrepancy).

[ArtF]

Well, if your cutting 6mm mdf at 2.5mm/sec your doing pretty well and should feel good
about your power levels I think. Id be interested in knowing at what speed you
can do 4mm acrylic cuts at near full power. By the way, tubes decay fairly slow even at
full power, so testing 10-15ma for a short cut wont typically hurt you any. (Did they specify
any maximum power? 15ma is pretty typical for the full power max..)

  How far way from your lens is the focus? Lenses are rated two ways, quality and focus distance.
Most of us have whatever quality is the best deal ( :) ), and the distance varies. The shorter the
focal distance, the higher the temperature on the dot. 1" lenses are for engraving shallow depth
for example, and they dont cut deep, but burn very hot. 2" - 4" lenses are for cutting thicker
items as the heat is focused over a deeper range at the focal point.. This is an important factor to know
when comparing laser between ourselves, the lens can make all the difference on what you do.

  For example, with a 1" lens, the focus is much more critical that with a 2" lens, you can be 1mm off with the 2"
and perhaps not notice, where with the 1" , 1/2mm may be as much off as you can be before not cutting..

  This is another thing that can cause power loss at a distance, the table being just a touch lower at the long distance
end. Not always of course, but it can help explain a problem.

  Ive only been playing for a few years with lasers, so I dont pretend to be an expert, I can only describe
what Ive found and what seems intuitive from testing. Over time we'll hopefully gather the expertise here
to explain oddities and maximize what we can burn..

  Feel the Burn..

Art

[Joakim]

On my laser the analog meter reads 0-30mmA and the laser starts to fire from 4-6mA. The maximum is about 17mA.
For cutting I have the following settings:


Material:Thickness:Current:Speed:
Acrylic3mm10mA350mm/min
Acrylic3mm15mA700mm/min
Acrylic5mm10mA220mm/min
Acrylic10mm10mA100mm/min
Plywood1/8" (3.18mm)10mA230mm/min


The settings works for cutting in the far end, except for the 15mA.
To me it looks like there are a linear relationship between thickness and power for a given current and material.

There is no real difference between 15mA and maximum 17mA therefore I choose 15mA as maximum to save the tube.

[Joakim]

The lens is the original 2" (50.8mm) focal length with the the curved side up. ZnSe type properly not high quality.
Mirrors are original, except for one I replaced as it got scratched.

[ArtF]

>>17mA therefore I choose 15mA as maximum to save the tube.

  Smart move, and about all you need to do.

>>To me it looks like there are a linear relationship between thickness and power for a given current and material.

Absolutely. The relationship to speed is also linear. Its all about energy/mm so power and speed are both linear to each other
for the most part. A cut at 100% at 12mm/s second is equal to a cut at 50% at 6mm/sec. on both of mine.

  It allows us to use either a pwm power correction for distance, or to change the feedrate to suit. I almost never use lower
power than near max, as their is no benefit other than burning certain materials. I will reduce power to stop scorching,
but when it comes to cutting or engraving I prefer to vary speed, as the job gets done in maximum time with no other
real effect that Ive been able to notice. (Though corners can burn differently at various speeds due to accel in the corners.).
(Auggie deals with that by providing a set power per distance moved. This keep accel from influencing the burn .. though
likely not perfectly and may require a calibration curve to be done on linearity to requested power.. thats the thing
that is most nonlinear I suspect. Just as mine wont fire until 27% request.. and yours fires at a different ma than anothers..

  All good information,
Thx
Art