My review of buying a Triumph laser.

[Scott Shepherd]

Would a four inch lens make a big difference?

How long does it take to switch between lenses?

A 4" lens would do worse on that material, in my opinion. I can't cut thick acrylic without air and a 4" lens gets the air nozzle so far from the cut, you get serious fire issues and blistering of the acrylic. 1" is just exceeding the ability of your machine. I know you are just trying different things to learn, but honestly, even if you could get it to cut 1" thick, it would be so slow that you couldn't make any money doing it.

[Robert Silvers]

^{Laser engraver vs Brother MFC-8710DW laser printer:}

[Scott Shepherd]

Y'all stop cheating and use upper and lowercase letters in your tests! It's a much better test because it'll test how your laser handles ascenders, descenders and things like the dot on an "i".

Let's see the 3 point font with upper and lower case using L, p,g,l,i, and letters like that.

[Robert Silvers]

1 mm/sec is not all that slow to me for something that I may do once or twice and where it does the work by itself.

For real use I plan to be at 9mm or less thickness.

Tell me more about air. I am trying to hook up a real compressor as I am getting very little air, and do have fire.

I ordered part number

5225K713

from McMaster-Carr - and I think that will do it for me.

[Dave Sheldrake]

Can anyone explain why more power at a faster speed is better than less power at a slower speed?

It's not, Lasers are more stable in their output at lower powers, as soon as you get into the 90%+ range you can easily cause the mode of the beam to become unstable.

If it is heat transfer causing distortion - I get it, except that yesterday I was told to turn down my power to get better cuts.

Uh huh, quite true, what is happening in your samples is you are trying to butcher through material way too thick for that type of machine (power rating).Laser cutting generates gas, much of that gas is CO2, CO2 blocks IR radiation causing sporaddic power to be delivered to the workpiece. Lower power causes less heat to be generated in the material avoiding meltback and core melting,If I ever cut thick acrylic (above 12mm) it gets done on a 600watt. What you are seeing in your samples is a tube that is too weak to cut 1 inch acrylic, the results may suggest more power is better but when you are at the limit of your available power something is going to give.

Would a four inch lens make a big difference?

On that thickness it would get worse, you would lose power density so it would be akin to trying to cut through a brick with a kitchen knife.

How long does it take to switch between lenses?

About 5 minutes.

This test seems to show that more power is better.

It is, but only when it's real power not the difference between 50 watts and 100 watts, try more power as in 800 to 1,000 watts to really see a difference.

cheers

Dave

[Dave Sheldrake]

Tell me more about air. I am trying to hook up a real compressor as I am getting very little air, and do have fire

More air will help if it is properly delivered, a 10mm nozzle standoff with a 5mm exit hole will cause the laser to striate the cut (making it look like a gear wheel), in the case of acrylic more air isn't always the best answer, you need volume but at lower pressure to stop pre-setting of the vaporised acrylic before the cut goes through.

cheers

Dave

[Robert Silvers]

First I need my milliamperes meter to see if I am even at real max power. I do seem to have Gaussian distribution at my current indicated max power setting.

I don't follow how less power means the work gets less hot. You have to slow down the cutting speed, so that gives much more time for heat to build up.

And again, I just saw a recommendation for 600+ watts, so that is suggesting more power is good, not less.

I am going to describe it as "Use your highest power where you have Tem00, which may be less than your max power so do tests to find out what your highest clean power setting is."

[Dave Sheldrake]

I don't follow how less power means the work gets less hot. You have to slow down the cutting speed, so that gives much more time for heat to build up.

Bigger power = beam mode issues, beam mode issues means heat distribution will be wider, you are trying to vaporise something and not induce carbon formation.More induced heat means a wider effect.

I do seem to have Gaussian distribution at my current indicated max power setting.

Based on? you have a DWC?

"Use your highest power where you have Tem00, which may be less than your max power so do tests to find out what your highest clean power setting is."

Cheapo Chinese tubes don't get TEM00

I just saw a recommendation for 600+ watts, so that is suggesting more power is good

Not it's not, it's suggesting a machine that has a 600 watt source is likely to be far higher quality than a cheap Chinese one, tubes of that power level in DC versions are usually GSI or similar, totally different ball game. The laser heads are different, the drives are different, the optics are different, the focussing methods are different, the air assist / gas assist is different, the pulse rates are different, the wavelengths are more defined + a bucket load of other differences.

First I need my milliamperes meter to see if I am even at real max power.

Due to manufacturing tollerance in Chinese DC tubes a meter won't tell you if you are at max power, for that you need an Ophir setup and a DWC. All a meter will tell you is if your PSU is pumping the correct current into the tube, it won't tell you if the voltage is right or even close. That's long before you get into polarisation modes and aberration issues.

cheers

Dave

[Robert Silvers]

Yes, I may or may not achieve the rated max power of my tube, but all I have control over is adjusting the power supply for current, so I can at least make sure that when set to 100%, it is not above or below 26ma of current - which is what RECI suggests to do.

So based on what I just learned, we can boil it down to energy density, for which watts are one part of that, but so is spot size and if your beam has an ideal distribution or not. And spot size is a function of original beam diameter, focal length, and wavelength. And then on top of that is pulses per second, for which glass tubes have limited control over, and RF is much more flexible for being optimal in that regard. And there is no market for cheap 600 watt units, so when people speak of higher power units, it is implied that it will also have better optics.

Here is my beam at 98% power (as indicated on the software) - how good or bad is this? Or do you need a side photo close to a clear edge? I don't have that because I did it on an unpolished edge, but I can cut it out.

[Dave Sheldrake]

Impossible to say Rob, you need a DWC to look at beam profiles instead of the effect of a beam on an unknown quantity (material)

There are a massive number of variables once the beam gets fired at a mirror or a lens (even when just passing through space) it gets very much into the realms of Particle Physics which while interesting can get a "glazed over" look from most people. Even at it most basist level, a simple thing like particles in the air between the incident point and contact point on the materials. If you have dust or smoke or vapour or gas in the air for example and that dust is above the wavelength size you get absorption or reflection, below wavelength size you get scattering.
That's just the effects of dust, well before the many other variables get taken into consideration.

Most of it can be summed up with "does my machine, Chinese or Western do what I want it to do"

If yes, the physics rarely matter
If no, then it gets complicated.

cheers

Dave

[Robert Silvers]

My beam diameter is 8.5mm at the location where I measured it. It may be 8mm at the muzzle.

The calculated spot size is about 0.0034 but I seem to be more like 0.008 in the real world. Those US lasers must look better from being closer to the 0.0034. If so, they would have about as much energy density from a 20 watt as I have from a 100!

So maybe I was wrong to compare my price to a 100 watt US machine. I probably could have compared it to a 40 watt.

[Dave Sheldrake]

A western 30 watt will do what an eastern 60 watt will do on average.

It's not quite so viable to compare RF to DC (budget types) as they are different animals and vary a lot in quality. That said a GSI Slc DC tube will kick any of the lower end RF's (sub 150 watt) out of the game park. It should do though, it's nearly $26,000. Chinese RF units are coming on fast, not quite "there" yet but doing well.

If you want a better , more defined spot from the Z4 get a meniscus lens from II-VI InfraRed, China tend to fit Plano-Convex's (usually the wrong way up as well) as they are cheaper but they area cheaper for a reason. Figure on a II-VI lens costing about 3x as much as an eastern version.

cheers

Dave

[Robert Silvers]

Has anyone changed to that lens and measured their spot size before and after? If it can raise my energy density a lot, I may want it. I don't think it need it for practical purposes, but I enjoy doing the comparison. What will it cost me?

[Robert Silvers]

http://www.parallax-tech.com/faq.htm#cut

"If we remove the perfect assumption (the lens is not perfect and the laser is not perfect) then you would be doing amazingly good if your lens and laser are good enough to give you a spot size of 100 micron diameter ( 0.1 mm ). You will be doing excellent if you get 200 micron ( 0.2 mm ) and very good if you get 300 micron ( 0.3 mm )."

When I first saw that with my beam diameter and focal length the best spot size that I could get was 0.08mm, and I had an actual spot size of about 0.2mm, and I knew that I was only achieving 1/6 of the potential energy density - it seemed like I should upgrade the lens.

But then I read on, and this FAQ says that 0.2mm is an "excellent" spot size and 0.1mm is "amazingly good."

"Therefore, if you get a CO₂ laser and an ordinary (affordable) ZnSe lens, you should be happy to get a spot size diameter anywhere from 250 to 500 micron = 0.25 to 0.5 mm diameter. From your spot diameter you can calculate the spot area and from there you can calculate your beam intensity at any power setting."

It says I should be happy, but I need to find out what I can expect for a spot size reduction with a ZeSe meniscus lens.

Here is how to figure that out:

http://www.iiviinfrared.com/resources/spherical_aberration.html

A Meniscus lens will have a spot size of about 1.5x smaller than Plano-convex.

That will change my power density from 3094 to 6938 watts per square mm, which is like keeping the same lens but bumping my power to 225 watts.

But then I saw someone else say that they would only increase cutting speed by 5%, which confuses me.

And I see them for sale ranging from $35 to $500, with no evidence that one is better than the other.

[Dave Sheldrake]

But then I saw someone else say that they would only increase cutting speed by 5%, which confuses me.

welcome to the exponential function. Power density is a measurement of power / area in 2 axis. Laser cutting is a product of power/area/depth (3 axis)

cheers

Dave