Author Topic: UV 2500mw laser focal point size  (Read 2943 times)

alurpal

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UV 2500mw laser focal point size
« on: June 27, 2016, 08:13:19 AM »
Hi everyone,

I am waiting on the delivery of my 2500mw laser from gearbest and was wondering what is an achievable focused beam size. I'd like to engrave small, detailed images on wood and silicone if possible but am trying to understand my hard limitations. I assume the real trick is getting the engraved medium set up at the correct height to intersect the focal point? Does anyone know the beam width at the focal point for a cheap, Chinese UV laser?

BTW, I am planning to flash latest compatible grbl firmware to enable pwm with the jumper mod.

Thanks guys.


Zax

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Re: UV 2500mw laser focal point size
« Reply #1 on: June 27, 2016, 09:16:28 AM »
You should be able to focus down to 100-150um spot size with the optics included, if you really need a smaller spot size a higher quality glass lens may help. The machine resolution is around 25um if belts and gears are optimized.

alurpal

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Re: UV 2500mw laser focal point size
« Reply #2 on: June 27, 2016, 09:42:14 AM »
You should be able to focus down to 100-150um spot size with the optics included, if you really need a smaller spot size a higher quality glass lens may help. The machine resolution is around 25um if belts and gears are optimized.

Thank you sir!

BritVic

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Re: UV 2500mw laser focal point size
« Reply #3 on: June 27, 2016, 11:08:53 AM »
also what is the optimum height above the work piece please?

Zax

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Re: UV 2500mw laser focal point size
« Reply #4 on: June 27, 2016, 11:29:56 AM »
That sounds like a trick question, as it isn't a fixed focal length optic.

The longer your focal length the better your depth of field, but the shorter your focal length the smaller the spot size.

So, if you focus to 1" vs. 2" you'll get a smaller spot size but it will be harder to keep it in focus if the material isn't perfectly flat to the axis.

BritVic

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Re: UV 2500mw laser focal point size
« Reply #5 on: June 28, 2016, 06:37:44 AM »
But ... would I get a deeper (more effective) burn focussed at 1" than I would say focussed at 2" or would the laser power difference be negligible?
Vic

Zax

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Re: UV 2500mw laser focal point size
« Reply #6 on: June 28, 2016, 06:52:56 AM »
The power difference would be negligible.

dindunuffin

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Re: UV 2500mw laser focal point size
« Reply #7 on: June 28, 2016, 07:15:21 PM »
How do you see to focus so small? I can see a dot about 1 mm at best.

BritVic

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Re: UV 2500mw laser focal point size
« Reply #8 on: June 29, 2016, 02:23:25 AM »
Put ya specs on sir! :)

Zax

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Re: UV 2500mw laser focal point size
« Reply #9 on: June 29, 2016, 05:00:50 AM »
Most of what you are seeing is scatter and reflections, not the actual beam. To accurately measure the beam you fire pulses and use a microscope to measure the results.

dindunuffin

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Re: UV 2500mw laser focal point size
« Reply #10 on: July 02, 2016, 08:49:07 AM »
So, we need thousands of dollars worth of scientific equipment to accurately operate a hundred dollar piece of hardware.  That's funny!

Zax

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Re: UV 2500mw laser focal point size
« Reply #11 on: July 02, 2016, 09:02:57 AM »
If you don't have access to a microscope (mine was $60) then just use a camera and zoom in. You won't be able to measure the size as accurately but you can determine the smallest size. If you put a ruler in the shot you can still estimate size pretty well.




dindunuffin

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Re: UV 2500mw laser focal point size
« Reply #12 on: July 02, 2016, 11:04:42 AM »
That's a good idea, I'll try the camera idea.  I had just been turning the focus back and forth, watching when it begins to leave focus each direction and blur, then split the difference. 

Zax

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Re: UV 2500mw laser focal point size
« Reply #13 on: July 02, 2016, 11:18:30 AM »
That usually works surprisingly well. You only need to optimize the power density for cutting thin materials, which also gives the minimum kerf width.

Cutting thicker materials and engraving is usually best focused into the material (cutting aim for about 1/3rd to 1/2th depth).

kn4ud

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Re: UV 2500mw laser focal point size
« Reply #14 on: July 02, 2016, 07:13:20 PM »
You can pick up a digital microscope for under $80 that is reasonable quality, I got one a few years back for $49 to check gem stones with. Works pretty good but the usb cable is way to stiff. I have had good luck by making a line (at low power) and looking at it with a 10x loupe and using calipers as a guide if you take your time you can get that line down to .1 to .15 mm which is a pretty clean sharp line. Now this is .004 to .005 inches , close enough for me. 99% of the time I use the loupe and calipers because the loupe is always in my pocket and calipers are close at hand and I'm too lazy to drag out the digital microscope.
Allen