How to Prevent "burn" marks when cutting paper

[Carol Stopforth]

I am sure I saw something about this previously on the forum, but I have searched way back and cannot find it.
Is there a way to prevent the brownish marks around the outlines when cutting paper? I cannot reduce power otherwise the paper won't cut. Or is this just an accepted "fait accompli" when cutting paper?
Also, thanks to all contributors to this forum, I learn so much just by reading though the various threads. Makes me realise just how much I have yet to learn.

[Joe Pelonio]

The combination of speed, power and frequency have to be adjusted for your machine. Higher frequency is more firing pulses. Too many burns edges, too few causes perforation instead of clean cuts. I have never had a problem with burned edges on paper with fast speed, low power and fairly low-medium frequency. On some machines frequency is called ppi.

[Vicki Rivrud]

Hi Carol,
Here again is the difference between Chinese lasers and others. We do not have PPI adjustments.

There is a fairly new controller offered by Lightwave that has the PPI function.

I have been speaking with Leetro about this problem and they are working on an upgrade but it will be a long way off before any release. They are still working on updating Lasercut, which has been years.

I have a 150watt and can cut paper cleaning without scorching. I use a multimat to hold down the paper, plenty of air assist, I even place a small fan inside the laser when cutting paper. I use high speed, low power but on these controllers we can not go below 8 or it gets a little hinky in its performance. Too fast will give poor results.

As with anything it takes lots of practice, test, test, test until you get the correct settings. If doing lots of paper projects some will say a galvo unit is better.

What watt do you have??

Vicki

[Carol Stopforth]

Hi Vicky, I have a 60 watt machine. For paper i set speed at 400 and power at 30%. These are the only 2 settings on the machine (as far as I know). Scorching is not major but you can see the light brown edges around the cut. I dont think I can put the power much lower else it won't cut through, maybe rev up the speed slightly? Yep, agree - test, test, test and practise till you blue in the face till you get it right. My machine is a Chinese CO2 laser, uses Laser Cut 5.3 software.

[Roy Nielsen]

Carol,

You can set the frequency on the advanced page. On the popup where you set your power and speed, there should be a little button with three dots, "...", click that and the first box should be "Laser Frequency". Mine defaults to 20,000. You'll need to experiment to find the best setting, but I've had good luck in the 100-200 range. You must click the "OK" button for the change to stick, if you hit "Enter" it will revert to the previous setting. Also, you may want to experiment with a lower power setting unless you're cutting through multiple layers. I think you'll find you have much more power at a lower frequency.

Roy

[Vicki Rivrud]

Hi Roy,
Are you refering to the pwm setting, which is 20,000?

It was always advised by the manufacturers that this setting should never be changed.

If you are changing it like "PPI" are you seeing any difference in the machine??

Vicki

[Roy Nielsen]

Hi Roy,
Are you refering to the pwm setting, which is 20,000?

It was always advised by the manufacturers that this setting should never be changed.

If you are changing it like "PPI" are you seeing any difference in the machine??

Vicki

Hi Vicki,

Yes, looking at my manual, that is the PWM frequency. No mention in my manual of not changing it, although I'm all ears.

By lowering the value to something like 50 to 200, depending on material, speed, and power, I'm able to cut faster and cleaner. Before I started experimenting with this setting, there appeared to be no power difference from something like 40 on up, e.g., running at 90 produced the exact same result as running at 40 at a particular speed (not quite getting through 1/8" birch ply). Due to the age of the tube (almost 3 years), even though barely used, I initially thought it might be the tube going bad (maybe it still is). I'll have to experiment with this more the next time I have some free time and a bit more 1/8" and 1/4" birch ply to sacrifice.

Back to topic, it seemed to me that when I was experimenting with the frequency setting early on using some typical notepad paper, that the lower settings did result in little to no detectable brown around the cut compared to something that could be seen slightly at the default 20K setting.

[Carol Stopforth]

Yes, there is a setting like that on my machine. I will experiment and let you know how it turns out. Thanks so much Roy.

[Roy Nielsen]

Carol,

You may want to do a little more research on the safety to your machine of adjusting the setting. I only have a couple hours or so on mine with low settings, not enough to determine if gradual damage could occur. Hard to say if the software has any built in protection or not.

[Mitzi Pages]

Hi Carol, may I know if you have successfully found the correct setting in cutting your paper? Like you, I also have a 60w China laser. I am trying to cut a 230gsm paper and was able to cut through using 100 speed and 70% power. I searched in this thread and found out 70% power is just too much but if I make it lower, it just wouldn't cut through, instead it will just leave a burnt marking on the paper. I also contacted my supplier and asked about the frequency setting. Same with Vicky, I was told not to change the setting of 20000. I am using a 23mm focus lens. Any info will be greatly appreciated. For reference, here's a photo of the paper. image.jpg

[Mike Null]

Mitzi

Welcome to SMC.

I do not have the same type of laser but I lower the power and also lower the frequency. The power and speed settings depend on the thickness of the paper stock. Your best bet is to test several settings. Vary the frequency first to see the effect of that then vary the power, then the speed. You should be able to find an optimum setting for each type of paper.

[Mitzi Pages]

Thank you Mike! This forum has helped me a lot. Regarding the frequency, my Chinese laser seems to lack this feature. There is a frequency box but I was advised by my supplier not to change the setting of 20000.

[Robert Walters]

Carol,

Since you don't want to mess with PPI/PWM and may not even be able to on your machine,
Give this a try and see what happens:

Create a grid of 10x10 1/2" squares (no fill, hairline outline, red if need be to CUT), spaced about 1/4" apart.

Across the top (left to right) create ten text field numbered 10, 20...90, 100.
These will be your POWER percentages.

On the side (up and down), create any ten text fields numbered 10, 20...90, 100.
These will be your SPEED in percentages.

If you "speed" goes from 0-1000, just divide by ten, and anything below 100 make 10.
You can always change the scale later on.

For example, If speed is:
1000 = 100%
500 = 50%
<101 = 10%

Start in the middle of the grid (50 power/50 Speed) and see what you get.
Go half (let's say 30% power or speed, your choice) and see what you get again.
If that's worse, try the other direction (70%), etc.

By the time you get done cutting all 100 squares, you'll know which combination of speed/power will work best
as you have gone thru every possible combination from 10/10 to 100/100 speed/power combinations and everywhere in between.

[Mitzi Pages]

Hi Robert, I will give this a try as this might help me solve my problems as well. Thank you!

[Vicki Rivrud]

Hi Roy,
Does your machine have the Leetro 6515 controller?

This is very interesting, have you adjusted the pwm often?

I went over my correspondance with the Chinese and they indicated that there could be damage to the power supply and/or the tube when changing the frequency so I have never "experiemented" with this. I really didn't want to have aby downtime hunting for the damage.

As I research this more, others are adjusting and there are controllers out that that mimic the Leetro products which have now include a "PPI" setting to be more user friendly.

Thanks
Vicki

Vicki