View Full Version : How to Prevent "burn" marks when cutting paper

Carol Stopforth
05-26-2013, 8:41 AM
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.:D

Joe Pelonio
05-26-2013, 9:15 AM
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
05-26-2013, 9:49 AM
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??


Carol Stopforth
05-26-2013, 12:19 PM
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
05-26-2013, 3:29 PM

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.


Vicki Rivrud
05-26-2013, 11:04 PM
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??


Roy Nielsen
05-26-2013, 11:40 PM
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??


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
05-27-2013, 2:41 AM
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.

Vicki Rivrud
05-27-2013, 9:28 AM
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.



Roy Nielsen
05-27-2013, 11:55 AM
Hi Vicki,

I'm not sure which controller I have nor do I know how to determine which. I would guess it has whatever the "typical" controller used by G.Weike was in 2010. Do you know how I might find out which I have?

I did find a manual dated May 2010 for LaserCut 5.3 on Leetro's web site that includes mention that the PWM setting can be adjusted from 200Hz to 200KHz (200 to 200,000). Not sure if the link will be modded out: http://www.leetro.com/english/down/LaserCut5.3%20Manual%20V1.6.pdf. Based on that, I'll likely adjust my method to run no lower than 200.

I have perhaps 2-3 hours of time running at other than 20,000, so probably not enough time to determine if it causes long-term problems. I'm still only doing hobby projects, mostly for grandkids, as I build my knowledge of the software chain, hardware, and substrates.

Roy Nielsen
05-27-2013, 11:58 AM

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.

Vicki Rivrud
05-28-2013, 8:34 AM
Hi Roy,
The best way to id the controller board is to open your side panel and look at the board. However more than likely if you are using Lasercut software it is probably a Leetro controller in 2010 the "typical" board was a MPC6515
If it is in an aluminum case then it is most likely an MPC6535

I asked Leetro about that very same statement and it was explained that the power setting on the PAD, which is set to 20,000 or 100% can be set to 200Hz to 200KHz (200 to 200,000) in values of % and that the machine config and/or frequency should be left at 100% (20,000).

With our new RECI tube we have our PAD power set at 80%/80% so that the tube isn't running at full power all the time.

So I am guessing in theory if you have your PAD at 100% and you are manually setting the frequency it must be achieving the same result as changing the power setting on the PAD.

I have sent a request to the Leetro engineers to answer this question.


Roy Nielsen
05-29-2013, 7:10 PM
Thanks for the photo and info Vicki. I'll try to take a look this weekend.

paul mott
05-30-2013, 11:03 AM
I did find a manual dated May 2010 for LaserCut 5.3 on Leetro's web site that includes mention that the PWM setting can be adjusted from 200Hz to 200KHz (200 to 200,000).

Just a thought, but that may just be a typo in the Leetro document.

I certainly would not want to pulse my tubes at a frequency in excess of 20kHz.


Vicki Rivrud
05-30-2013, 9:07 PM
I received an answer from the engineers at Leetro . . . . the pwm adjustment is only for radio frequency tubes. As I use a CO2 RECI tube, it is analog and the adjustments to PWM would do absolutely nothing. Further more the majority of CO2 tubes are analog. They did however warn me that if the pwm adjustment was made too high it could damage the power supply and the tube. As for Lasercut, they are promising, again, a release in June. I'll keep everyone posted. Vicki

Mitzi Pages
06-26-2014, 11:52 AM
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. 292008

Mike Null
06-26-2014, 2:32 PM

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.

Robert Walters
06-26-2014, 3:05 PM

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
06-27-2014, 9:02 PM
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.

Mitzi Pages
06-27-2014, 9:04 PM
Hi Robert, I will give this a try as this might help me solve my problems as well. Thank you!

Kev Williams
06-27-2014, 10:42 PM
we have our PAD power set at 80%/80% so that the tube isn't running at full power all the time

re: the 80%/80% setting on the pad-- and I'm basing this on my Triumph laser and the PHcad software that runs it (which I believe is very similar to Laserworks and Laser Cut)

My software has a "laser mode" setting, either "auto" or "manual". I'm sure Laserworks and Laser Cut has a similar setting.
--- when in AUTO mode, the power and speed settings the laser will use are those set in the software, and the pad settings are ignored. The pad will show the software settings while the laser is in use, then revert back to the pad settings when the laser is done...

--- when in MANUAL mode, the power and speed settings the laser will use are those on the laser's touchpad, and the software settings will be ignored.

Also, my pad has 2 power settings, "Power 1" and "Power 2" which can of course be set individually. The power setting I want can be chosen from the software. But again, the main software power settings will be ignored.

Finally, when firing and/or slewing the laser from the pad, the laser will use the pad settings, not the last settings sent by the software.

When in auto mode, the pad settings will not act as a 'laser limiter'. I have the 'power 1' on my pad set at 8%, so I can test fire without much burn. I don't even know what 'power 2' is set at!

Question about the paper cutting problem-- is the table being cut on solid or open (like honeycomb)?