How about the speed parameter?

[Rikard Strand]

I'm new to laser cutting.

Today i experimented with the speed parameter. I notice that the cut was better with lower speed but the cutting time was almost the same in the intervall about 5-100%. When i lowered the speed under 5% i notice a bigger differens in time.

Can anybody explain this?

The power i used was between 15-25%.

Rikard
- - -
Mercury LaserPro 30w, 2.0 lens.

[Viktor Voroncov]

Which material you are trying to cut? I just cut 1,5 mm Rowmark with Mercury 40 Wt and settings were Speed 1,6% Power 100%

[Rikard Strand]

Now trouble cutting. Just trying too understand the speed parameter. I thought it should be a "big" difference in speed. With the naked eye it looks almost the same between 5-100%. But i understand by looking at the cutting that it's a big difference.

[Richard Rumancik]

I notice that the cut was better with lower speed but the cutting time was almost the same in the intervall about 5-100%. When i lowered the speed under 5% i notice a bigger differens in time.


Rickard - your post jogged my memory so I searched and found this old post of mine.
http://www.sawmillcreek.org/showthread.php?t=60072

Briefly, on the Mercury, what I found that the 42 ips specified as "maximum speed" applies to rastering only. For vectoring, you will probably get only about 11 or 12 ips. This occurs at around 30% setting. Going above 30% will probably not have any real effect on speed (job time). It is rather misleading that the driver lets you set a parameter that is actually "out of range". If it defaulted back to 30% for inputs above 30%, then at least you would know what was happening. You should see a change in job time below 30%; at least I did.

So in reality I think you were saying you did not see a big dfference in job time between 5 and 30% (because I am saying that 30% speed is the maximum it will go even if you enter a higher value.)

I do not understand why you did not see a more significant difference between S30 and S5, as I found quite a measurable speed difference. Unless you were cutting paper, and P25 was considerably more power than needed such that it cut through at both speeds. I really can't explain what you may have observed here.

Keep in mind that at speed = 2.9% the laser will change to CW mode so at that threshold behavior (cut quality) can change considerably.

But also note speed (and thus job time) is not at all linear to the % setting.

It's been a long time since I did this - maybe repeat some of the tests I described and you will get a better handle on your laser functionality.

[Niklas Bjornestal]

What kind of object are you cutting? If the laser need to change direction very often you wont see any big difference in speed since it wont have time to accelerate to the selected speed before it needs to change direction again.
If you try to cut a large square you will probably see a much higher difference in speed.

[Rikard Strand]

I was actually cutting paper:)

With this knowledge i will try to cut multiple papers. Today i cut one paper with good quality at P4/S15. I will try lowering the speed and power to cut multiple papers.


Keep in mind that at speed = 2.9% the laser will change to CW mode so at that threshold behavior (cut quality) can change considerably.

CW mode? "cut quality" for better or wears?

Thank you Richard you been big help! Now i understand much better.

- Rikard (Swedish spelling for Richard)

[Dan Hintz]

CW = Continuous Wave... lasers are generally broken down into pulsed and CW. Pulsed lasers usually have a higher peak power but within a short period of time, or a pulse, whereas CW lasers have a lower output power but run continuously at that power. Because of this difference in behavior, material cut with a pulsed laser will have a different outcome than the same material cut with a CW unit. When you're moving slowly, it doesn't really matter if the laser is pulsing because the distance between one pulse to the next is very small... as you speed up, the distance would increase and cause a rough edge, so the laser shifts to CW.

[Richard Rumancik]

Rikard

You asked about my comment regarding CW mode at speeds below 2.9%. This applies to the LaserPro Mercury - I can't say if or how it applies to other GCC products/models. And I do not know if other manufacturers do something similar or not.

Your question prompted me to try to look it up in the manual, but I couldn't find anything. Sometimes you think you "know" something and then can't figure out where the info came from.

I believe it orginally came from correspondence directly from GCC many years ago. But to be honest the communication from them was quite confusing. However, I did find a pdf Technical Bulletin from Jorlink which talks about the Power Ramp function.

As far as Power Ramp is concerned, GCC has not provided a very coherent explanation, but the jist of is is that with power ramp enabled, it will adjust the energy delivered on the corners of a vector shape by changing the pulsing. It needs to do this when it cannot keep a constant speed due to deceleration/acceleration. By turning power ramp on, it will deliver less energy on the slow turns so that they are not overburned.

The English is not the best, but I think what they are saying at the end (in the "Reminding Notes") is that IF you are using POWER RAMP, then at speed = 3% and below, you will have "full duty cycle" (continuous wave; CW) and above 3% speed you will be "modulated duty cycle" (subject to your PPI setting I assume).

IF Power Ramp Function is disabled, then it appears that it is CW (continuous wave) at all speeds (changing PPI should have no effect.)

My take on this is that below 3% speed, there is no significant acceleration affect and therefore they don't need to "tweak" the power on the corners. So, if I understand correctly, setting speed at 3% and below (I originally said 2.9) will cause the laser to lase continuously.

You asked if this will cause the edge to be better or worse. I don't know - it probably depends on the material. I just wanted you to be aware that at or below this speed your PPI setting might be ignored.

I have not verified these statements with experiment so if someone else has any input or interpretation please contribute.