How breaking a lens increased my laser power

Discussions on optics for laser cutter/engravers

How breaking a lens increased my laser power

Postby twehr » Thu Apr 26, 2012 12:33 pm

About once a year, it seems, I manage to destroy a lens. It happened again a few days ago.

Broken Lens.jpg


I ordered a new one from LightObject, but went for a higher quality lens this time. The difference is pretty amazing. It actually boosted by effective cutting power by quite a bit. And the few extra dollars it cost was well worth it.

If you want to read more about it - look here.
tim
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Re: How breaking a lens increased my laser power

Postby TLHarrell » Thu Apr 26, 2012 4:19 pm

Good writeup, Tim. I will have to remember this if I ever mess up my lens, or decide it is no longer serviceable. Also checked out your YouTube video of the unwrapping of the laser tube from Quiangdenzensatisfaction (or however you spell it). Exactly like my big burrito was when it arrived last month. It was my first replacement on my 40w FSE laser. Amazing how much packing material they use. I've got enough to supply my shipping needs until I order my next tube I think.
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Re: How breaking a lens increased my laser power

Postby sports.racer » Thu Apr 26, 2012 7:53 pm

Noob question. What causes the lens to break?
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Re: How breaking a lens increased my laser power

Postby twehr » Thu Apr 26, 2012 8:33 pm

sports.racer wrote:Noob question. What causes the lens to break?


We really don't know for sure. Some say it is letting it get too dirty. Could certainly be the case for me. I hate removing the air nozzle and retaining ring, etc. But maybe I'll try to make myself like it more in the future. :P
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Re: How breaking a lens increased my laser power

Postby Techgraphix » Thu Apr 26, 2012 9:11 pm

Just a thought.. do the nozzle and lens get warm/hot? Is it possible the lens gets crushed because its space in the nozzle gets smaller (too small) with higher temperatures?
In that case it might be solved with a flat rubber ring between lens and retainingring?
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Re: How breaking a lens increased my laser power

Postby awesomenesser » Thu Apr 26, 2012 9:32 pm

twehr wrote:
sports.racer wrote:Noob question. What causes the lens to break?


We really don't know for sure. Some say it is letting it get too dirty. Could certainly be the case for me. I hate removing the air nozzle and retaining ring, etc. But maybe I'll try to make myself like it more in the future. :P


Are you just tightening the lens in the aluminum mount or have you added one of the o-ring mods. My lens hasn't broken yet but I don't use the laser all that often.

I do really like the idea of 15-20% more power though. I was looking at Light object and noticed they have a [ur=http://www.lightobject.com/High-quality-20mm-ZnSe-Focus-lens-F750mm-P671.aspxl]70mm focus high quality[/url] lens. Does anyone know if there is a disadvantage to having a long focal length? The loss of 2cm in table height isn't a big deal to me (I really only cut acrylic). It seems like a big advantage to be able to have a more defined (thinner) beam through thicker materials.
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Re: How breaking a lens increased my laser power

Postby twehr » Thu Apr 26, 2012 9:38 pm

awesomenesser wrote:
twehr wrote:
sports.racer wrote:Noob question. What causes the lens to break?


We really don't know for sure. Some say it is letting it get too dirty. Could certainly be the case for me. I hate removing the air nozzle and retaining ring, etc. But maybe I'll try to make myself like it more in the future. :P


Are you just tightening the lens in the aluminum mount or have you added one of the o-ring mods. My lens hasn't broken yet but I don't use the laser all that often.

I do really like the idea of 15-20% more power though. I was looking at Light object and noticed they have a [ur=http://www.lightobject.com/High-quality-20mm-ZnSe-Focus-lens-F750mm-P671.aspxl]70mm focus high quality[/url] lens. Does anyone know if there is a disadvantage to having a long focal length? The loss of 2cm in table height isn't a big deal to me (I really only cut acrylic). It seems like a big advantage to be able to have a more defined (thinner) beam through thicker materials.


The 70 mm will give you a greater depth of field (longer focus area for deeper cuts), but a wider kerf. If you want a narrower beam (kerf), then you need to go to a shorter focal length lens.
tim
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Re: How breaking a lens increased my laser power

Postby TLHarrell » Thu Apr 26, 2012 9:43 pm

Yeah, that lens in the OP looks REALLY really dirty. I would think that the possibility exists that eventually the beam passing through the clouding would start to heat it, causing a single point high temperature spot in the center of the lens. At some point, the change in temperature causes a thermal shock. Not sure about how your local temperature and humidity play into it, but it's likely part of the cause.

I think I'm going to start cleaning my lens a little more often.
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Re: How breaking a lens increased my laser power

Postby educa » Sun Feb 03, 2013 11:47 pm

But what do you need to clean your lens?

What solvent?

And cotton sticks or cloth ?
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Re: How breaking a lens increased my laser power

Postby TLHarrell » Mon Feb 04, 2013 10:31 pm

I've found by far the best cleaner for laser cutter smoke is a vinegar/water mix. Nothing else seems to budge it, but the vinegar takes it off like magic. Little bit on a nice soft rag, rub between fingers.
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