[bpoulin]

I'm looking at a few different Chinese lasers, and I'm wondering the Glass CO2 lasers, what's the big difference between, 80, 100, and 150w? Can you do more with a more powerful laser, or is it the same thing, just does it faster because it cuts/burns faster? And at what point does it just become overkill?

[Tweakie]

It was established, many years before lasers had even been thought of, that all materials have an optimum cutting speed. Cutting too fast or too slow yields poor results and bad surface finish etc. etc.
To a certain extent this rule also applies to lasers. Wood, in particular, exhibits extremely sooty edges if cut too slow and in order to cut it quickly and reduce the soot more power is required. On the other hand acrylic likes being cut slowly so lower power can be tolerated.

So basically, what I am saying is that the maximum laser power requirement is pretty much related to the materials you intend to use.

There is a minimum setting associated with most glass tube lasers which means that you can't just turn down the power from a high power device to match the exact characteristics of a low power device. (not sure if that makes sense) As an example I have great difficulty getting a fast enough (constant velocity) axis speed and low enough laser power output to avoid cutting through thin card in places when all I want to do is mark the surface.

Don't know if this helps.

Tweakie.

[bpoulin]

I think I understand, from what I've read most of the glass tube lasers won't fire if you set it below 20, I'm assuming that's %of power? So if you have a 40w laser that's somewhere around 8w of power but if I have a 100w laser that would be more like 20w of power? What stinks is I don't have one single item I want to repetitively engrave. I have friends in the catering business so I'm looking for wedding and party engraving referrals from them, I plan on also hitting up the local wedding shops. I also do sandblast stone signs, and I'm hoping to break into grave stones and be able to laser etch photos on to granite. And finally I want to do some images burned on to live edge wood slices to sell at the flea market for some extra cash up front while I build the contacts to do the other things with the engraver. Now with that all said, I'm thinking of using an 80w laser because I'll actually be doing very little cutting, mostly photo or letter engraving on the surface. But I'd like some input on what power would be best for what I'm doing? Should I be looking at lower or higher power, or is 80 fine? It's a bit expensive to do this by trial and error lol.

[derekja]

Even 80 is high for mostly engraving. It'll work great, but may be higher than you need.

As a data point, the TechShop in Menlo Park has 3 Epilog lasers, one 60W and two 45W.

Just an indication of where one shared-use facility has decided the sweet spot is in terms of price and what you can do.

[bpoulin]

I was under the impression that Epilog used RF lasers not CO2? And that translated to 45w epilog would be equal to 90w CO2? So that would put the closest I could get to the sweet spot would be an 80w? Please correct me if my information is wrong, I'm completely new to this, so all I have is 2nd hand information.

[Tweakie]

I think you have picked up a bit of crossed information there buddy.

(The Epilog RF lasers are still CO2 it is just the method by which the atoms are excited that distinguishes RF from DC [glass tube]).

Tweakie.

[bpoulin]

So Watt for Watt are they the same? Will 60w RF and 60w DC have similar or the same cutting/engraving power?

[Tweakie]

Tough question that.

The power density per square cm watt for watt is quite obviously the same (assuming they have both been measured by the same yardstick) but RF lasers tend to have a larger diameter beam at a distance of 1 Meter and this can lead to a better focused dot and therefore create more cutting power. (smaller the dot, higher the power).
The introduction of a beam expander, collimator and increased beam path coupled with better optics is just one improvement that Epilog have made to create smaller dot size and much finer engraving capability. This same technique could just as easily be applied to DC excited lasers although I don't know if anyone has actually done it.
Another difference that may have effect on some materials is that DC excited lasers are almost always circular polarization whereas RF is almost always plane polarized.

Doesn't really answer your question but throws a few more variables into the ring.

Tweakie.

[Tweakie]

What I was trying to think of earlier was HPDFO illustrated by this fine example compared with my meager effort.



Tweakie.

[bpoulin]

Wow... Tweakie, A genuine thank you followed by a very sarcastic THANKS!!! way to not answer the question and create a million more lol. I am a photographer so I understand polarization, but what does that have to do with the cutting ability of a laser?

[Tweakie]

Your guess is as good as mine here that's why I said "may have effect.....".

There are lots of articles on the net and here is just one I was reading the other day. Polarization | II-VI Infrared

Tweakie.

[andy55]

in general if you have a high-power laser and want to reduce the power output what you do is you put a polarizer in front of it and rotate the polarizer to a suitable angle. This way you can adjust 0-100%. The polarizer lets some of the beam through and either absorbs or deflect 90-degrees the rest. If the deflected beam potentially creates damage then you want to make sure you have some kind of beam-dump device which safely absorbs the beam.

This simple approach with one polarizer results in an output polarization that rotates when you rotate the polarizer. If your mirrors and focusing optics don't like that then the usual way is to use a combination of a half-wave-plate first and then a polarizer. The polarizer is now fixed and does not rotate, but instead the half-wave plate is rotated to adjust the intensity.

If you have a circularly(random?) polarized laser and you put a polarizer in front you will probably loose 50% immediately. If the output is really circularly polarized (and not random) then it's possible to do a 0-100% adjustment but you probably need two quarter-wave plates in addition to the half-wave-plate and the polarizer.

I'm not sure who sells this kind of CO2 optics which can take the power-levels, and would be hobbyist priced. The CO2 laser is 10.6 microns when all the normal laser optics is for near-infrared and visible which is roughly 0.5-1 microns...

my 2cents. cheers,
AW

[zax15uk]

So Watt for Watt are they the same? Will 60w RF and 60w DC have similar or the same cutting/engraving power?

In theory they should be very similar (spot size, quality, DOF and other factors will have some effect), but the DC excited glass tube is likely to degrade faster than an air cooled metal tube RF laser.

Another option, 2 x 40W tubes and a beam combiner provide 80W for cutting and can be used for low power engraving if necessary. In general if you have sufficient XY speed it shouldn't be an issue although I do agree with Tweakie that some materials need lower power and slower speeds to get the optimum result.

Zax.