I need a laser that will start a fire.

[Blueteeth]

Ok, I think we should get off the topic of lasers here - although that would remove any shred of 'electornics' which is what this forum is all about

In terms of a problem to be solved - altohugh I am no expert in tree-felling, or landscaping - but started a fire at say... a foot from the top, will not cause that top foot to drop. As many have mentioned, getting it to a point where it sustains burning is difficult laser, or no laser, and as heat generally travels upwards

<tangent> When wood is heated it releases 'wood gas' which burns, the actual wood itself merely gets heated, the gas is flamable, combusts, creates heat, so it rises, heating the wood above it, when releases more 'wood gas' etc.. etc..if wood burnt directly, there would be no jets of flames coming from embers, or flames at all for that matter</tangent>

So I can see the logic behind this, and perhaps EVEN the idea of using a laser because its about creating a focused point of ignition at a distance that is difficult to get to (you wouldn't get me up a 50 foot ladder leaning against a wobbly tree). But my last words on this is that

a) would require a very powerful continuous beam laser. I am unaware of any solid state device capable of the 100W+ needed to do this that can be focused any further than a few inches. CO2 lasers are IR, used for welding. They are invisible, difficult to focus far, so aiming it and adjusting the optics would cost far more than hiring someone to chop it up bit by bit. Visible lasers just don't have the power, except perhaps a 100W argon (that's again, 20x than hiring out an entire of team of guys to do this). Any other form of laser is generally pulsed. A Nd:YAG lasers often boasts kW power - but pulsed so the average power (required for continuous heating of poor conductors of heat ie: wood) is too low.

a) *ammendum* just because a 5W laser can set fire to a bit of paper, doesn't mean to say it'll do it to wood. The target needs to absorb as much energy from the beam as possible. Not to mention tinder, kindling, all of hich would need to be stuffed in a hole dirlled in the tree - so you woudl HAVE to go up there anyway.

b) Burning the pole/tree in stages, starting at the bottom of a top section would simply leave you with a very sturdy lump of charcoal, which would spit embers around everywhere as it burnt, creating fires here there and everywhere.

c) You will have to accept that it is either going to cost you to hire out someone to do it for you. Hire out your own equipment and risk injury, or just wait for it to fall on something expensive.

d) If you're really after the cheapest option, which involves more time and effort than money - befriend someone who has experience in this, and owns a chainsaw. Do HIM a favour, and he might help you out.

If you manage to do this with a laser, cheap or otherwise, without harming anyone I will personally go over there and buy you a beer. Nice idea, but impractical. If you really want to see what happens, then why not buy a 20-30W laser off ebay? calculate the optics needed (all lasers have divergance, how small that is just depends on how accurate the optics are). It'll cost you >$100, and you'll be disappointed.

I do not in any way mean to discourage brainstorming and idea's, thinking is good, but the reaction from others was one to bring you back down to earth :/

 

[Blueteeth]

Seriously, I think you are going to need a bigger laser.
"Full sun" is about 1,000 watts per square meter. So a 5w laser is about the same as using a 3" diameter magnifying glass in the sunlight.
It's easy enough to make some burn marks, but have you ever gotten a fireplace log to burst into flames with a handheld magnifying glass?

A cheap 20x20" fresnel lens can melt metal. But you are right in that to ignite a 'log' you need more. More than a match, and more than a blowtorch because to heat a large object of poor conduction, it takes time which is why theres tinder (burns easily and burns out quickly), to kindling (needs sometihng to get it started, burns for a while) to the main fuel (requires sustained high temps for a long period in order for it to become self sustaining).

Anecdote:
Whilst at university, as the only smoker I had to go outside to smoke (which I prefered). One night, it was cold and raining, I flicked the butt over by some bushes, where it landed in the middle of a 2-foot wide, 2-foot high stump from a cut-down tree. I went out for a second cigarette 4 hours later only to find the entire stump was glowing orange (it was still raining). There were no flames, and the earth around it was scorched, and bone dry (rest was mud). I can only guess that it had plenty of dried sap in there which fueled it, and took the fire to the core of the stump. The next morning it was still smoking, we smashed it open with an axe and it was all coal and ash - like powder, but was sitll pretty tough.

 

[gary350]

Seriously, I think you are going to need a bigger laser.

"Full sun" is about 1,000 watts per square meter. So a 5w laser is about the same as using a 3" diameter magnifying glass in the sunlight.

It's easy enough to make some burn marks, but have you ever gotten a fireplace log to burst into flames with a handheld magnifying glass?

You are right about hard wood that is not rotten. But what you don't understand about this tree is, it is so rotten I can poke my finger through it like poking a hole through styrofoam. Limbs that fall off can be crumbled up into tooth pick size pieces by hand. I have ignited tree limbs that fallen off with nothing but a match. The limbs brake up easier than balsa wood or styrofoam and burn up in only a few minutes in the BBQ grill. Even though it is extremely rotten it still have a lot of weight for its physical size it can still smash a fence, smash roof, smash an storage shed if it falls 50 ft. One of the last limbs fell off this summer it busted into so many pieces I had to use a rake and shovel to clean it up and it burnt up like a pile if dead leaves it was gone in a few minutes. It won't take much to set this tree on fire. If I thought the tree would break in half when it falls and hits the power lines I could cut it and let if fall. After falling 30 ft a 1000 lb tree is about = to 3000 lbs when it hits the wires.

 

[tcmtech]

If its that rotten then my cable saw method would be an easy and safe way to get it down in pieces for very little cost.

 

[DerStrom8]

You are right about hard wood that is not rotten. But what you don't understand about this tree is, it is so rotten I can poke my finger through it like poking a hole through styrofoam. Limbs that fall off can be crumbled up into tooth pick size pieces by hand. I have ignited tree limbs that fallen off with nothing but a match. The limbs brake up easier than balsa wood or styrofoam and burn up in only a few minutes in the BBQ grill. Even though it is extremely rotten it still have a lot of weight for its physical size it can still smash a fence, smash roof, smash an storage shed if it falls 50 ft. One of the last limbs fell off this summer it busted into so many pieces I had to use a rake and shovel to clean it up and it burnt up like a pile if dead leaves it was gone in a few minutes. It won't take much to set this tree on fire. If I thought the tree would break in half when it falls and hits the power lines I could cut it and let if fall. After falling 30 ft a 1000 lb tree is about = to 3000 lbs when it hits the wires.

Another thing, have you considered the legality of burning a tree in your yard? In some places that wouldn't be legal, simply because of the chance that it could spread. You know, I'm sure some forest fires have started because some guy wanted to take the removal of an old tree into his own hands. You should be very careful. I highly recommend you just hire a professional. $200 is a small price to pay for a pro, compared to the $200,000 in destroyed property due to a forest fire. Please consider the cons, as well as the pros, of your ideas.
Regards,
Der Strom

 

[duffy]

A cheap 20x20" fresnel lens can melt metal.

I said a 3" magnifying glass, which has 7 square inches of surface area, 5W at full sun.

You are comparing it to something fifty times bigger - 400 square inches of surface area, collecting some 258W at full sun. Fifty times more powerful than a 5W laser.

 

[Blueteeth]

I wasn't comparing a fresnel lens to a 5W laser. Just highlighting that using solar power for heating *can* be practical. For 'burning things' at a distance, a parabolic reflector, a couple of lenses, and as long as its sunny you can have something which will happily rival a powerful laser. Lasers aren't specifically for 'burning', they are a single wavelength - the wonderful thing about sunlight is, it covers the spectrum nicely (ok, NOW I'm comparing the two..)

 

[Warpspeed]

Why a laser ?

Seriously, why not some gasoline and a match ?

 

[tcmtech]

If you are really set on using light to burn things the magnifying glass trick works even better if you use a 100w Halogen car headlight bulb encased in a tube that has a shiny aluminum foil liner as the light source!

With the right sets of lenses you can focus that spot at considerably further distances than the few inch distances a normal magnifying glass lens works at. I don't think 50+ feet is doable but still its a light based burning system just the same.

 

[Reloadron]

If its that rotten then my cable saw method would be an easy and safe way to get it down in pieces for very little cost.

I vote with tcmtech, that or a skilled friend with a saw who knows what he is doing. My neighbor takes out my unwanted trees and I keep his computer running and have done his house replacement wiring.

This is not going to happen with a LASER.

Ron

 

[duffy]

use a 100w Halogen car headlight bulb encased in a tube that has a shiny aluminum foil liner as the light source!

If the aluminum foil is the light source, what do you need the halogen bulb for?

Or do you mean use the foil as a reflector? If so, why not just use a headlamp reflector?

Sounds like you're saying you can start fires by putting a magnifying glass in front of a headlamp.

 

[DerStrom8]

If you are really set on using light to burn things the magnifying glass trick works even better if you use a 100w Halogen car headlight bulb encased in a tube that has a shiny aluminum foil liner as the light source!

With the right sets of lenses you can focus that spot at considerably further distances than the few inch distances a normal magnifying glass lens works at. I don't think 50+ feet is doable but still its a light based burning system just the same.

I'm not sure about that, tcmtech. The reason you can use a magnifying glass with the sun is because of the huge distance you are from the sun. If you hold a magnifying glass up to a regular light, you won't be able to focus the light on a single point like you can with the sun. On the other hand, you're talking about an extra reflector, which might make the difference. That's worth experimenting with....

 

[tcmtech]

I take it not too many people ever tried putting magnifying glasses in front of different types of lights to see what does what.

Didn't you guys ever watch Macgyver?

 

[DerStrom8]

Didn't you guys ever watch Macgyver?

Didn't you ever watch the Mythbusters Macgyver specials?

 

[Blueteeth]

MacGuyver > MythBusters. MB is about entertainment, bigger fires, bigger sparks, shoddy guesswork science. MacGuyver was a religion.... (sitll have my lock of Richard Dean Andersons hair somewhere...)

 

[DerStrom8]

MacGuyver > MythBusters. MB is about entertainment, bigger fires, bigger sparks, shoddy guesswork science. MacGuyver was a religion.... (sitll have my lock of Richard Dean Andersons hair somewhere...)

Hahaha, I get your point, but MB is still more scientific than MacGyver

Lately I have been seeing what you said about the mythbusters more and more, but in some cases I think they hit it right on. I hate to say it, but some of those ones are the MacGyver myths

 

[tcmtech]

Well if you guys are so sure you cant burn something with a magnifying glass lens and a car headlight bulb I suggest you go out in your driveway and try it on your hand first!

If you have a good light and a good lens its not hard to focus that light and its heat down small enough to burn things.

 

[DerStrom8]

Well if you guys are so sure you cant burn something with a magnifying glass lens and a car headlight bulb I suggest you go out in your driveway and try it on your hand first!

If you have a good light and a good lens its not hard to focus that light and its heat down small enough to burn things.

As I said, putting it in front of a reflector might change how it works, so I'm not really doubting right now. I haven't tried it, so I can't say that it doesn't work. I'll just take your word for it

 

[shortbus=]

How about termites and a helium balloon or kite? Put the termites in a little basket and let the balloon or kite fly them to the top of the tree and they'll eat there way down. Saw it work in a cartoon one time, so I know it works.

 

[duffy]

Ok, I was [LATEX]\not\textsf{\tiny{d}}}\not\textsf{\tiny{u}}}\not\textsf{\tiny{m}}}\not\textsf{\tiny{b}}}[/LATEX] curious enough to try this. It gets warm, but is no way hot enough to start a fire -





Yes, that's the high beams, and, granted - the fresnel's not as large as it could be, and that parabolic reflector isn't giving a round spot (need a hemispheric reflector for that) but even so, this just ain't gonna do it.