Beam shape when it hits the surface slightly oval?

Discussions on optics for laser cutter/engravers

Beam shape when it hits the surface slightly oval?

Postby bloq » Wed Dec 02, 2015 9:13 am

Hey,

i am not sure about the following: My laser works well with minor adjustments to be done. What i am a little bit uncertain about is the shape of the laser beam when it hits the surface. When i test the laser with the fire button the shape looks oval. I thought this should be perfectly round? I could not detect that the beam hits something in its way but maybe the more experienced people around here know what this could be?

thanks a lot

tm
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Re: Beam shape when it hits the surface slightly oval?

Postby sshwarts » Wed Dec 02, 2015 6:48 pm

Is this with the nozzle installed or removed?
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Re: Beam shape when it hits the surface slightly oval?

Postby bloq » Wed Dec 02, 2015 7:50 pm

with nozzle installed ...
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Re: Beam shape when it hits the surface slightly oval?

Postby sshwarts » Wed Dec 02, 2015 9:29 pm

Try it with the nozzle removed. I'm betting the beam is hitting the nozzle. With my particular set-up I had to make and extension to move the nozzle down, closer to the work.

laser-focalEn.jpg
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Re: Beam shape when it hits the surface slightly oval?

Postby bloq » Thu Dec 03, 2015 2:20 pm

you are absolutely right!! So my nozzle is not aligned correctly? If the last mirror is hit exactly in the middle it should also go straight trough the lens, shouldn't it? or do i miss something?
My nozzle did not really fit from so i made a delrin adapter. This is of course not really accurate ...
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Re: Beam shape when it hits the surface slightly oval?

Postby sshwarts » Fri Dec 04, 2015 2:48 pm

It could be alignment of the nozzle but more likely your nozzle is too close (or I suppose too far away) from the lens. If you have say a 50mm lens, then the focal point (the point we want to be doing the cutting with) is 50mm from the lens. If the nozzle is too close to the lens, then beam before it converges to the point might be striking to opening of the nozzle or the body of it.

Scott
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Re: Beam shape when it hits the surface slightly oval?

Postby Techgraphix » Fri Dec 04, 2015 4:36 pm

Why not try it with the nozzle removed.. then you know if the ray hits the nozzle..
Kees
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