[dingbat]

In terms of laser tube power, when is a Watt a Watt?

I've been using a UK built laser (a CCT) with a 30W air-cooled RF tube - a tiny wee thing. With this I've achieved work that others (with experience of Chinese lasers, using water-cooled DC glass tubes) have said would need an 80W or even a 100W tube.

So is there any real comparison between nameplate Watts and cutting power, when we compare between DC & RF tubes? Should power for machines like Epilogs be seen realistically as twice (or more!) that for the glass tube brigade?

It was also noticeable that this air-cooled tube had almost no cooling applied to it, certainly compared to the sort of pumped-water chiller units essential for bigger Chinese machines.


I'm looking at a Lasersaur build (a DIY design based on Chinese tubes), as a way to get a big laser for 8x4 sheets of plywood. Although I'd probably have gone for the biggest tube anyway, do I still need a reality check before assuming it's a simple upscale from a real tube machine.

[Tweakie]

Consensus of opinion on the Sawmill Creek forum is that the RF tubes have about double the power of the DC tubes (watt for watt maker's stated power rating).
I have both DC and RF tubes but no way of actually measuring the output from either so can't actually prove it but I am pretty sure they are right.

Tweakie.

[dingbat]

For the benefit of Lasersaur builders, are there any good sources for an RF tube & PSU at a sensible price? Even for an insensible price! It would still be a way to get a high-end machine at a mid-range price.

[txcncman]

Watt almost always describes electric power consumed to do some work. I believe the energy output of a laser is actually measured in joules. Now, go try to find that in your machine documentation. There are many factors in determining the actually "power" of a laser. Not only is it how many joules are output, but how they are focused, the distance from the work surface, airborne particles, etc. A 20 "Watt" laser with a 1 mm beam, focused down to 0.25 mm will seem to have a "similar" power of a 80 "Watt" laser with a 1 mm beam that stays focused at 1 mm.

[Mariss Freimanis]

A Watt is a unit of power. A Joule is a unit of energy. 1 Joule equals 1Watt of power for 1 second.

Mariss

[txcncman]

Mathematically one can be converted to the other. But I am pretty sure the laser builders are telling how much energy has to be put into their lasers to operate and not how much energy is coming out of the business end. That was the main point I failed to make.

[Tweakie]

But I am pretty sure the laser builders are telling how much energy has to be put into their lasers to operation and not how much energy is coming out of the business end.

I suppose it could be a matter of efficiency but I always put it down to the Chinese manufacturers over rating the performance of their tubes.

Tweakie.

[Rodney Gold]

I have both RF tubed and Glass tubed lasers , there is no way that the RF lasers are "worth" double a glass tubed in respect of power or processing, my 60w Glass tubed laser cuts almost 2x the speed of my 30w RF using the same lens. (at about 1/10 the cost of the RF tube)
I have compared outpur of my 60w and 80w Reci tube to my RF tubed machines *synrad and coherent* , in terms of quality of engraving , both RF and glass are identical. In terms of cutting , the glass is better , in terms of machine engraving (rastering) thruput , the chinese lasers are about 1/2 the speed of my top RF unit *Gcc spirits* but that has nothing to do with the tube but more to do with the motion system.

[Tweakie]

I bow to Rodney's expert knowledge here (if anyone knows then he knows) but he still has a way to go before he has convinced the Creeker's

Tweakie.

[cinematic2]

Do not forget about REAL laser power.
Most of chinese laser machine sellers use to lie about real power.
700mm long DC excited laser is not 40Watt.
It is 32-35W when new.
1000mm long laser is not 50W but at least 40-43W.
When new.
But Synrad laser called 25W (48-2) is 33-36W when new.
25W is AVERAGE power between new and spent.

[Rodney Gold]

I dont think some ppl can ever be convinced that a laser engraver of 1/5th the cost of their's can perform as well. They then moan when others underprice them , if you don't have to amortise expensive capital equipment , you can do stuff cheaper....
As to "lying" about power , well my reci tube is rated at 80w , it has a test label on it stating it was tested at 89 watts , however the real difference is that the glass tubes will fail far sooner if run at 100% power , so we run 90% max power as a default ..ie 80w tube runs at 72watts...
Doesnt really make much difference re lying over wattage , the "expensive" reci tube is around $450 to replace whereas a 30w synrad is about $3000, a "cheap" 60w Glass tube is $180 or so. Even if the glass tubed lasers are 1/2 the power of a RF one , its still $180 vs $3000. The 20 000 hours usage touted by RF mnfgrs is also a "lie" , I have never got more than 3-4000 hours of use from either a Coherent or synrad.

[dingbat]

''700mm long DC excited laser is not 40Watt.
It is 32-35W when new.''

Does anyone know the behaviour of these tubes when aging? I understand that all of the "nameplate" figures quoted here are electrical power, not optical (i.e. input power, not the useful output power delivered in the beam). Assuming that there's better efficiency in the RF tubes, then the difference in cutting power for the two types is no surprise.

A separate question though - as the tubes age, their output power certainly falls and presumably this is mostly because their efficiency has fallen too. However I'd be quite surprised if their electrical input power changed by quite so much. Has anyone actually measured this?

[Rodney Gold]

As the tubes age , they leak gas and drop in output power , eventually failing , as they heat up , they also can drop in power unless your cooling system is very good. Ideally you want to run at less than a 90% duty cycle and use a chiller that will maintain an exact constant temp to get the best out of the tube.
We have multiple lasers here , RF and CO2 and all can vary due to different factors.
We "test" each laser at least 2x a week. Its an easy test , we have a setting for cutting JUST thru exactly 3mm Acrylic and run this test at the top left , top right , middle and bottom left and right of the table. If we need a correction due to power loss we input it into an excell spreadsheet of "settings" for all the different lasers so that all settings are "exact". It is a huge problem as we have 3 of one type , 3 of another and then 2 chinese machines and EVERY laser puts out its own different power and has different speeds - the chinese have speeds in mm/sec and the 6 GCC machines have speeds as a percentage of machine speed and the 2 different GCc models have different machine speeds.

[dingbat]

I made myself a very simple optical power meter. It's a snippet of MDF (or acrylic) with a grid of short lines cut through it. The lines are cut at varying tube powers and cut speeds (the ease of setting this up does vary, according to your software). Cut the grid, turn it over and see which ones have burned clean through. You'll see a roughly triangular arrangement with a vague line marking the boundary between "cut" and "not cut".

Try it on a couple of identical machines, and you can see the effects of tube life.

Try it on two different machines and you can see the effect of RF vs. DC efficiency. Assuming that "tube power percentage" is a linear proportion of the electrical input, I'm indeed seeing that a 30W RF tube on one machine is cutting like an 80W DC tube on another.

[Tweakie]

Dingbat,

A couple of photo's would be great.

Tweakie.

[muqtadir]

Rodney
What is your experience for Chinese laser tubes between normal and RECI tube ? Which type is good for long run and your 80 watt. RECI can engrave on Metals (scratch better than CerMark) ?
Thanks.