Interpolating Laser Settings

[Ernie Martinez]

Is there any rule of thumb for interpolating Laser settings when a given power described is different than what you're using? For example I have a piece of Granite which says:

For a 35 watt laser use 40-45% power and 35 IPS or ~45% speed. But how would I interpolate that for a 50 watt laser? I know I'm going to have to experiment, but I'd like a starting point, since all examples I see are for lower power lasers.

Thanks
Ernie

[Mike Null]

Ernie

It's critical that you know the raster speed in inches per second of the machines you are trying to compare. If somebody gives you a number of 35 ips then you just need to know what the raster speed of your machine is, ie. 100 ips, you set the speed at 35% or 35 ips.

Power works the same way so if somebody says run at 35% power you need to know what the full power rating of their machine is then adjust your settings accordingly.

Further, 45% of 35 watts is 16 watts, etc., etc.

[Ernie Martinez]

Well that makes perfect sense :)

Thanks

[Rodne Gold]

There is a direct correlation between power and speed , ie if you have a 25w laser and you use a speed of X , then for 50w you would use 2x.
HOWEVER on a lot of lasers , x speed has a far more tenuous relationship to 2x , especially when doing small objects where the X axis barely has a chance to reach its speed due to accelleration , de accelleration and so forth.
You can extrapolate fairly well on YOUR laser , ie if you upped your tube from 1x to 2x , you can fairly confidently extrapolate speed to 2x , but using another lasers settings , even the same make of yours , can be fraught with difficulty. You can use this perhaps as a start point , but cannot rely totally..as you have said , you have to do test strips on YOUR laser to get the best results

The easiest way to get a thumb suck start point for any material is to use your past experience , for eg , you know you need x power and y speed for acrylic engraving/frosting , then start with that speed / power on , lets say, rowmark laserable stuff as it acrylic based. Same for cutting , you have a setting for 3mm acrylic , so halve the power or double the speed for the 1.5mm Rowmark material.
There have been many posts about setting up a database for various machines and materials , the reason there isn't one is that every laser differs and there is no golden formula.
Even my laser mnfgr's published settings for my laser and my power are not even close to what we actually use... so much for settings!!!

[Jiten Patel]

Mike,

I was told by Trotec by the guy who designed most of their machines in Austria that power percentage doesn't work like that. Say you have a 100w tube and fire it at 30% power, that doesn't mean you are using only 30w of power and isn't the same as a 30W tube firing at 100% power. It means that the 100w tube is firing 30% of the time at 100w.

We found this out when we trialled a 100w galvo before we bought ours and were using it at 30% "mimicking" a 30w or so the sales person told us. When we finally got our 30w, we were cutting much much slower even though we were using 100% power - around 2/3 longer. Spoke to Gernot in Austria and he explained that the sales person was completely wrong and explained the above to me. Now this may be complete rubbish, but thought I would throw it out there for discussion.

[Mike Null]

Jit

Having retired from the appliance industry I was aware of what you describe with respect to microwave ovens but had not heard that it also pertained to lasers. (it is quite easy to detect with a mwo by just listening to it)

In my experience it is hard to verify that statement relative to co2 lasers based on visual or audible evidence however it would seem to me to be a simpler less expensive way to regulate power.

Even so, I think the method provides a reasonable basis for comparison.

[Rodne Gold]

I think the glass and RF tubed lasers do vary power , full power with variable time would be equivalent to PPI, and thus varying power would by definition vary PPI as power decreased .... which might not work that well....

[Mike Null]

Chuck

We're really talking about rastering for comparison as few mfrs post their vector speeds. In fact the only one I know of is Trotec.

[Walt Langhans]

In trying to deiced what laser to get I was going to ask a similar laser power question, and this thread pretty much answered it, however what's raster speed and rastering?

[Rodne Gold]

Rastering is when the laser acts like a dot matrix printer , vectoring is when it acts like a pen plotter

[John Johnson 2]

Jit,

A CO2 laser is a current controlled device. The laser runs at between 15,000 and 22,000 Volts and 0-25 milli Amps. Given the extreme high voltage it is not feasible to turn a 100W lasser on 30 % of the time. By implication the control circuitry would have to switch 15,000 volts on and off for 30% of the time. Now think about it. If you are ably to set DPI it means that the laser has to be on each time it fires a dot. This means that your 30% on time has to be able to reconcile with the fire time of each dot which in turn means that it would have to be on for 30% of the time of each dot firing.

laser power is NOT 100W 30% of the time. it is 30% of the input current which if roughly 25mA. You must also remember that laser cutting power may not have a linear relationship with input current. 50% of input current may not direct be 50% of output power.

The 100W 30% of the time theory may step from the fact that the power supply is a high frequency PWM modulated switch mode supply.

[Dan Hintz]

Say you have a 100w tube and fire it at 30% power, that doesn't mean you are using only 30w of power and isn't the same as a 30W tube firing at 100% power. It means that the 100w tube is firing 30% of the time at 100w.
For metal RF tubes, this is the correct explanation... for those who are familiar with PWM (pulse-width modulation), this is the exact method.

You should also consider this PWM in terms of discrete "blocks" of power. Let's say the "block" is 1ms in length of time. Every millisecond, the laser runs for 300us at 100% power and then turns off... that's your 30% power. Now, if we only enable power once every other "block", we get a 50% cut pattern... every 4th block and we have a 25% cut pattern. Moving at 1"/second, turning on a "block" of power only every 100th time would make a pattern of 0.2" long cuts interspersed with 0.2" long tabs (i.e., perforations).


A CO2 laser is a current controlled device. The laser runs at between 15,000 and 22,000 Volts and 0-25 milli Amps. Given the extreme high voltage it is not feasible to turn a 100W lasser on 30 % of the time. By implication the control circuitry would have to switch 15,000 volts on and off for 30% of the time. Now think about it. If you are ably to set DPI it means that the laser has to be on each time it fires a dot. This means that your 30% on time has to be able to reconcile with the fire time of each dot which in turn means that it would have to be on for 30% of the time of each dot firing.

laser power is NOT 100W 30% of the time. it is 30% of the input current which if roughly 25mA. You must also remember that laser cutting power may not have a linear relationship with input current. 50% of input current may not direct be 50% of output power.
For glass DC tubes, this is the correct explanation...