Variable laser power

[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

[Joakim]

Art:
You're right that must be the relationship between power and cutting. Energy per cubic mm removed material - It makes sense as the laser has to evaporate the material from the cut.

Would be nice to set the laser current with the S parameter from GCode. Like 0 to 100 (0% to 100%) given a current from 0mA to 15mA in my case. Easier to change between light engraving and deep cutting in same job.

Blueyonder:
This is the type of laser I have.
http://www.ebay.com/itm/High-Precise-40 ... 0825065645

Is your the same type?

[Blueyonder]

Yes, looks the same as mine.

[Blueyonder]

I'm cutting some 2mm MDF at the moment using 3mA @ 6mm/s and cutting fine with those settings so thought i would try the linear theory. I doubled the power to 6mA and doubled the speed to 12mm/s cut it needed two passes to cut through the material. Is this what you would expect?

[ArtF]

Hi:

>>I doubled the power to 6mA and doubled the speed to 12mm/s cut it needed two passes to cut through the material.

  There are some related losses so its not quite linear, there is a temperature climb rate to allow a material to burn,
so Id expect to be able to double it, and lower that by 10% or so. SO from 6mm/ssec to maybe 10mm/sec, its about what I usually
do.

    Easy enough to allow an S word to control power, as Ill be making the max and min PWM settable, I suggest a usage of
0 - 100% as the power no matter what kind of laser, we'll just have different PWM settings.. as to max and min...

Art

[Blueyonder]

Just ran a test while cutting 2mm MDF at 6mA and 3mA power settings at speeds from 20mm/s down to 5mm/s. I have attached a photo of the results as seen from the backside of the material. The 6mA is not a great improvement over the 3mA?