What happens if...

[Peter Boyford]

...I remove the lens from the laser? Might sound like an odd question, but there is reason behind :)

When laser cutting thick materials the edge seems to be slightly slanted as an effect of the defocusing the further away from the focal point you get. Also for some engravings people seem to recommend to set the machine a bit out of focus to get a larger beam width.

Now - what if i remove the lens completely? The beam would then be straight (it is all the way from the laser source to the head) and have a bigger diameter. Would this do anything in order to cut/engrave stuff where the ultra thin line is not essential?

Best regards
Peter

[Karin Voorhis]

Funny you should ask this cuz by accident just last week I forgot to put my lens in after a cleaning took forever to figure out why I was not firing.... Without the lens there will be no cutting at all...... no laser just the red light......

[Peter Boyford]

Howcome? Some kind of protection device activates without the lens?

[Vicky Orsini]

I could be wrong, but I thought the lens focused the laser beam to a point at a fixed distance (normally 2"). Without the lens, you're firing a beam with no focus, so it's not actually hitting anything.

[Joe Pelonio]

Most likely :confused: it's just so far out of focus that it's diffused, and there's not enough concentrated power left for it to do anything.

[bruce cain]

Sortta like sunlight through a magnifying glass.

[Lee DeRaud]

The only way a 25-50W laser can cut anything is by getting all its power into a really small spot...otherwise you might as well be using a flashlight.

The typical beam diameter coming out of the tube is measured in millimeters, typically in the 4-8mm range. The lens focuses that down to 0.005" or so, bumping the energy density of the beam up by over 1000X.

[Larry Bratton]

The only way a 25-50W laser can cut anything is by getting all its power into a really small spot...otherwise you might as well be using a flashlight.

The typical beam diameter coming out of the tube is measured in millimeters, typically in the 4-8mm range. The lens focuses that down to 0.005" or so, bumping the energy density of the beam up by over 1000X.
Right..ain't nothing magic about it. It's just a highly focused beam of light. Kinda like when you were a kid and took a mirror..caught the sun just right..cast it upon some flammable tender..grass etc..and started a fire. Like you said, without the focus you may as well use a flashlight !

[Alexander James]

You should still have some measure of power in an unfocussed beam. This is demonstrated when doing alignment checks...With a piece of masking tape in the path of the beam (upstream the lens), you are able to burn a hole quite easily in the masking tape with a 30W laser. I would imagine with more power, depending on the substrate you should be able to mark, engrave or even cut without the lens.

Alex

[Lee DeRaud]

I would imagine with more power, depending on the substrate you should be able to mark, engrave or even cut without the lens.Easy enough to test, even with the lens in place. Assuming you have a 2" focal-length lens, just drop the table 2" from the in-focus point. (Dunno how it works on an Epilog or whatever, but I would just tell my ULS that the material thickness is 2" more than it really is.) The width of the beam at that point is pretty close to the same as the beam width upstream of the lens.

Now run a job, any job, with the settings you would normally use for that material. On MDF with 25W, I get a barely visible burn mark, less than you'd expect from stubbing out a cigarette on it.

I was being slightly facetious with my "flashlight" remark, but if I had a 25W flashlight that would focus down to a 5mm spot, I'd get the same result. It's just a question of power per unit area.

[Mike Hood]

Actually... couldn't resist running down to the shop and trying it. With the lens off, I can cut 1/8" ply if I slow Waaayyyy down (2% speed, 100% power)... but it's an ugly thing... :)

One sortof cool thing is you can speed up to 20% and 100% power and draw 1/4" wide lines at a pretty nice clip. I suppose a guy could do some sort of drawing or something. Never tried it before... but there's still some pretty serious energy coming out of the beam without a lens.

[Gary Hair]

When I had some alignment issues last year, the tech person had me remove the first mirror and lean a piece of plywood against the wall. I did a test fire at 10% power and it burned the wood - it was about 8' away and the burn mark was less than 1/8" in diameter. All the lens does is focus the beam to a point where it is the smallest diameter possible. If you defocus to a longer distance than optimal then you are probably going to lose a lot of power fast as the beam gets wider and wider until there's not much left of it. I believe that if you don't run it through a lens then it will travel quite a long distance and remain relatively the same size.

It would be interesting to hear from a laser tech to see what they have to say.

Gary

[Peck Sidara]

Peter,

I think the best word that describes doing this is ugly. This should apply to most if not all C02 lasers out there. Without the lens, the beam is unfocused and will yield a wide, ugly burning of the material. It's not recommended.

Instead, check w/ your manufacturer to see if they offer a longer focal length lens like a 2.5" or 4" if the standard is 2". A longer lens has more depth of field and will provide straighter cuts.

Focusing in the middle of the substrate vs. the top should also help.

[Rodne Gold]

Peck , albeit I run GCC's , I have found longer lenses will reduce power density and can make cutting thick stuff well nigh impossible as you run outa power or the speed is so slow you get major edge heat affected zones. Sometimes changing lenses is a double edged sword.

Peter , try cutting perspex , it acts as a wave guide and wont allow divergence . if for example 8mm pex has visible sloping sides , its most likely a beam alignment issue, the beam HAS to hit the lens dead centre. However I have never seen lower power lasers with std lenses cut thick stuff with absolutely straight sides , the best we can do is minimise slopes.

Apart from that ,as a precaution check your autofocus distance is accurate and that the table itself is leveled up.

[Peck Sidara]

I'm not sold on that Rodne. I've cut 3/4" poplar wood using our 4" cone lens. I couldn't get thru the same thickness using a 2" cone lens due to the beam "going out of focus".

A 4" lens will have a longer focal length, depth of field, wider spot size and should increase cutting depth ability.

Just me $.02