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FrozenGate by Avery

Whats that Smoke ?

M

Mosc007

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Feb 2, 2012
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Oooops.

I was at a mates place showing him some tricks with my M140 Lab laser.

I had it pointed at a Light Grey wall about 3 meters away. I thought Very Light Grey Paint would be ok.

After doing some CD Case Buring, Lighting Matches etc we noticed some smoke from his wall.

This is a Very Light Grey Paint. It is Plywood underneath. Not Gyprock or Drywall.

We had a close look and their are 2 Burn marks in the Wall. Both are several mm Deep.

After seeing it burn the Painted Plywood we tried on another peice of unpainted Plywood. It Burns thru the first layer of Plywood in a short time. When it gets to the second layer it stops burning. The second layer must be harder wood.


Looks like you gotta be carefull what color Paint you point it at. Even Very Light Grey Burns. And this is only running at 1023ma.


Charles
 

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I hope both of you were wearing appropriate Laser Safety
Goggles/Glasses...


Jerry
 
Yep, Thats why we didn't see it burning untill after.


Charles
 
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Mosc007 said:
It Burns thru the first layer of Plywood in a short time. When it gets to the second layer it stops burning. The second layer must be harder wood.
Click to expand...

It doesn't work like that. There comes a point where the shape and surface area of the hole allows the heat to be dissipated into the wood without causing much chemical alteration. Prove this to yourself by using a 2x4. It's all the same wood, but it will still stop before going all the way through.
 
Thanks for the info.

What concerned me was that such a light colored paint still absorbed enough light to start burning. I knew how quickly black stuff burned but not lighter colors.


Charles
 
These 445 lasers can usually blast through white paper at 5m distance. I don't point it at anything burnable.
 
I just tested it on White Paper.

Even at a few inches it does nothing at all. Just reflects a Heap of light back. It doesn't even warm the Paper up.

Dark colored paper does burn thru quickly though.


I have always had mine pointing past the Kitchen into the Toliet. The wall in their has very light colored Yellow Paint. It has Never left any marks No matter how long I leave it on. It reflects a lot of light though.

I wonder if the problem with Light Grey Paint is that Light Grey Paint still uses a small amount of Black Pigment. It didn't refect a huge amount of light back. That alone should have told me it might burn. I just assumed being a light color it would not burn.


Charles
 
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If you end up upgrading to a certain style of gas laser that emits 10's of watts of energy in an invisible beam, the toilet room will need to be used for its original purpose, not a beam dump :P

(sorry, couldnt resist!)

If you say the yellow wall in there reflects a lot of light, then either not enough energy is being absorbed by the paint, or the energy density isnt high enough (laser not tightly focussed).

My 445 properly focussed cuts through a dark beer mat (coaster) with ease at a metre or more.
 
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Hehehe. 10 Watts would certainly cause some serious Damage if Focused.

I am only running around 1.2 Watts. It did damage a Light Grey Painted wall at 3 Meters but hasn't even left the slightest mark on the Light Yellow Wall. The Light Yellow must have a high reflectivity. I am using a G2 Lense and focused to best Beam I can get. Using my Glasses I can look closely at the Spot and adjust the Focus well.

I too have played with Darker colored Paper. Red Paper starts burning straight away. Even Bare Plywood starts smoking and burning quickly.

For something to burn, enough of the light has to be absorbed by the surface. Dark colors absorb a LOT more light than lighter colors. White paper with a 95% reflectivity will only absorb 5% of the light. Not enough at these powers to burn.


Charles
 
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Mine only runs about a watt too - I was jokingly suggesting that if you ever get a carbon dioxide laser, I'd suggest picking somewhere else to dump the laser beam :)
 
When cutting with a CW beam, especially burning into a pit, the smoke and crap coming off will tend to defocus the tight beam limiting the cut. That's why cutting lasers have gas assist or are pulsed.
Hmike
 
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Thanks for the Info Hmike. That probably explains why it only cuts about 3mm into the Plywood.


Charles
 
Mosc007 said:
Looks like you gotta be carefull what color Paint you point it at. Even Very Light Grey Burns. And this is only running at 1023ma.
Click to expand...

Its not really that surprising. If a wall absorbs 30% of incoming light its color would be considered light grey. The effect of a laser is 3 times smaller than on a completely black wall... so you could expect the same result from a 1 watt laser on a grey wall as you'd see with a 300 mW laser on a black wall.

An additional effect is that the paint may darken once it starts to heat up a char a bit, increasing absorption etc. This would typically happen when you burn a hole through white paper as well. Consider that white paper relfects only up to about 90% of light (for the best premium paper) - cheap office paper is often as low as 80% and still considered white by most people.
 
I might try the White paper again but this time use a cheap Laser Copy Paper.

I was using a High Quality Inkjet Printer paper.


Charles
 
Yes some white paper is glossy and others have a matte finish you have to try several before you say it will not burn white paper :)

I burn white business cards all the time, seriously !
 
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