Ghost image while cutting

Discussions on optics for laser cutter/engravers

Ghost image while cutting

Postby hoda0013 » Thu Mar 03, 2011 7:31 pm

It seems like sometimes, depending on the height of my workpiece relative to my focal point, I get a faint ghost image when I am cutting. For instance, if I cut a circle, the toolpath that I want to cut gets cut, but a faint ghost image of the circle will also appear offset from the original circle. The ghost circle is faint and just marks the workpiece (rather than cuts it), but it is a cosmetic blemish nonetheless. I assume this is due to some misalignment in my mirror / lens assembly. Has anyone else had this problem? Does anyone know the cause?
Thanks.
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Re: Ghost image while cutting

Postby trwalters001 » Thu Mar 03, 2011 7:56 pm

Hi Dillon,

I'd look for your beam clipping an edge inside the lens/mirror assembly. It could be that the beam is off-center and reflecting off of something inside the housing. If you put a piece of paper or acrylic at the input hole to the lens assembly and fire a pulse, does a ghost show up there?

Tim
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Re: Ghost image while cutting

Postby hoda0013 » Thu Mar 03, 2011 8:05 pm

Thanks for the tip. I've put paper over the input hole to the lens assembly before to see the location of the unfocused beam. At the far reaches of my table the spot size is close to the input hole size so it is very possible that I'm clipping an edge on the way in. I'll have to look a little closer tonight and see if it needs a little adjustment.
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Re: Ghost image while cutting

Postby trwalters001 » Thu Mar 03, 2011 8:15 pm

"the spot size is close to the input hole size "

Really? How big is your input hole? (On the lens housing... :shock: :lol: )

On my lens assembly, it's about 1/2" diameter. I hope your beam isn't that big...
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Re: Ghost image while cutting

Postby hoda0013 » Thu Mar 03, 2011 8:49 pm

Haha. I'd have to measure the beam, but I'd guess the input hole is 1/2" and the beam size is about 3/8", so not too much room for error.
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Re: Ghost image while cutting

Postby trwalters001 » Thu Mar 03, 2011 9:10 pm

That's a pretty big beam diameter. How big is the mirror inside the lens housing?

That may be where it's happening. The beam is elliptical on the 45-degree mirror, so it's spread out even bigger.

The first laser I bought (ebay - about 4 months ago) had a beam diameter of about 3/16" @ 3' from the laser.

I haven't fired up the one from Full Spectrum yet. I'm going to try to this weekend.
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