Lens diameters

[SScnc]

I posted in another thread regarding if using a 38.1mm lens makes a noticeable improvement for engraving versus the 50.8mm I have now, but no one replied. If anyone has any experience with this please let me know your thoughts.

However, I'm going to order a 38.1mm and just want to verify the correct diameter(s) I can use. I have the stock head and I have everything aligned and working so great I don't want to take it apart to measure the lens at this time.

So will this 20mm lens work in my head ? http://www.lightobject.com/High-quality ... -P809.aspx

Or this 18mm one ? http://www.lightobject.com/High-quality ... -P799.aspx

[brian257]

The 38.1 mm lens will make a big difference in your engraving, but I would recommend going all the way down to a 25.4mm lens if you are going to engrave small text.

[Techgraphix]

I don't know what a "stock head" looks like but you can measure the diameter of the lens you already have in it.
If your head has a tube like this one: http://www.lightobject.com/Pro-laser-he ... -P586.aspx,
It's quite easy to build in a beam-expander.. With the length and internal width of the tube a 3x expander can fit in perfect. Your engraved results will come out even more crisp than without.
(A beam expander like this will do: http://www.lightobject.com/3X-Beam-Expa ... -P718.aspx
i managed to laser text with such an expander in my 38.1 HQ lens with a height of 0.2mm, i had to use a very strong magnifying glass to read it back....but i could read it
Think of an average postcard has thickness of 0.7 mm, that means that i could write 3 lines of text on the side of a postcard .. Aligning the postcard is almost impossible, however..

To fit the beam-expander in the tube, i took out both lenses and turned a tube that fitted tight in the tube.

Kees

[DonL]

Question regarding small fine engraving...

I am using a 38.1 lense and when I look at the lines closely, the dots just touch each other, If I go to a finer point, how do I increase the resolution so that the dots are not spaced apart? For example, I want a verticle line engraved as a solid verticle line not a dotted verticle line.

Do I increase the stepper driver or replace the steppers to a motor with a finer step? or is this not an issue?

and even with the upgrades, is the small K40 just not capable of .2mm text - too much play in the design? I can get clear text at 1mm so I am good with that - I would not want to go smaller but if I did.... Could I?

Thanks.

[Techgraphix]

To get the scanlines closer just make the value of scangap smaller, like 0.04 or even smaller instead of 0.1
Ok, the engraving will take longer to finish.
A K40 is not build that well to expect superb results.. Even a CO2 lasertube has its limits, for real fine details you need another machine with an RF-laser but you can buy a nice car for that money..

Kees

[DonL]

To get the scanlines closer just make the value of scangap smaller, like 0.04 or even smaller instead of 0.1
Ok, the engraving will take longer to finish.
A K40 is not build that well to expect superb results.. Even a CO2 lasertube has its limits, for real fine details you need another machine with an RF-laser but you can buy a nice car for that money..

Kees

Thanks! I will try that setting. I plan on retiring in a couple years and using the laser as a source of added income so all this training and practice has a purpose. I may invest $20,000.00 if it looks like I can make that back in a year or two.

[SScnc]

I don't know what a "stock head" looks like but you can measure the diameter of the lens you already have in it.
If your head has a tube like this one: http://www.lightobject.com/Pro-laser-he ... -P586.aspx,
It's quite easy to build in a beam-expander.. With the length and internal width of the tube a 3x expander can fit in perfect. Your engraved results will come out even more crisp than without.
(A beam expander like this will do: http://www.lightobject.com/3X-Beam-Expa ... -P718.aspx
i managed to laser text with such an expander in my 38.1 HQ lens with a height of 0.2mm, i had to use a very strong magnifying glass to read it back....but i could read it
Think of an average postcard has thickness of 0.7 mm, that means that i could write 3 lines of text on the side of a postcard .. Aligning the postcard is almost impossible, however..

To fit the beam-expander in the tube, i took out both lenses and turned a tube that fitted tight in the tube.

Kees

Thanks Kees. I did just now remove my lens as I wanted to clean it again anyway and it's 18mm diameter. That is amazing that you can engrave that small !!!. I'm not familiar with a beam expander and how it works, do you have a link to info about how it works please ?

Brian, I haven't found or even heard of a 25.4mm F lens on LO website, I'll do some research on that, thanks.

[Techgraphix]

Try google "laser beam expander".. The type I mentioned above has a small diverging lens and a complementary bigger converging lens.. De distance between those two gives you more or less widening of the laserbeam. So with the lenses of a 4X expander you can make a 3x or 2x expander.
Ofcourse the biggest lens has to be wider than the laserbeam times the magnification..
It's optic science to calculate that a wider beam gives you a smaller focuspoint.. Formulas can also be found on the internet..

Kees

[DonL]

To get the scanlines closer just make the value of scangap smaller, like 0.04 or even smaller instead of 0.1
Ok, the engraving will take longer to finish.
A K40 is not build that well to expect superb results.. Even a CO2 lasertube has its limits, for real fine details you need another machine with an RF-laser but you can buy a nice car for that money..

Kees

Thanks! I will try that setting. I plan on retiring in a couple years and using the laser as a source of added income so all this training and practice has a purpose. I may invest $20,000.00 if it looks like I can make that back in a year or two.

I looked every where and I don't see that setting... I see Pen Space X and Y which is set to 0.00 and I see Curve Dispurse that is set to 0.10
no 'SCANGAP" Please illaborate....

[SScnc]

Don, you're looking in the wrong place. It's not in LaserCAD system options, it's in the settings on the right hand side of the graphics page under control panel in "Layer options" where you set speed and power for your job. Double click that and you'll see scangap at the bottom of the popup under "Engrave Parameters".

[Tech_Marco]

Just a reminder to you folks that not every machine can take 2.0x or bigger beam expander!

For example: 60W laser, 20mm mirror, 18mm focus lens.
The beam diameter roughly 6mm.
Mirror usable area: 12.14mm or 12.0mm is the limit. To be more realistic by taking divergence into account, 10mm is more practical.
So, 6.0mm x 2 = 12mm the beam will be over the workable area. In this case, you can only use 1.5X beam combiner.

If your machine comes with 25mm reflection mirror, then you can use 2.0x beam expander for the 60W tube. The usable area from a 25mm mirror is 15mm. By the way, you do need to check the laser head intake hole diameter because most of those laser head comes with 14mm in diameter.

If the tube is a 100W with 8mm beam diameter. After 2.0X, the beam size will be 16mm. It will exceed the limitation. Again, you can use 1.5X beam expander only. To be safe to say, only 80W or smaller power with low divergence can use 2.0x beam expander. Only a 40W laser tube with 4mm or less can use 3.0x beam combiner.


Marco

[Techgraphix]

That's why I modelled the beamexpander in my laserhead.. my beam is ~5mm and my lens is 20mm (~18mm effective). I had set my expander to ~3x
For high power lasers a beamexpander can be necessary to reduce the power/mm^2 on the mirrors but with my humble 60Watts that's no issue..
Aligning is much easier too: there is nothing to align..

Do you know if such build-in expanders do exist?? I've never seen them or heard from something similar..

Kees

[DonL]

SScnc .... Got it! Cheers....

[Tech_Marco]

That's why I modelled the beamexpander in my laserhead.. my beam is ~5mm and my lens is 20mm (~18mm effective). I had set my expander to ~3x
For high power lasers a beamexpander can be necessary to reduce the power/mm^2 on the mirrors but with my humble 60Watts that's no issue..
Aligning is much easier too: there is nothing to align..

Do you know if such build-in expanders do exist?? I've never seen them or heard from something similar..

Kees

Kees

How could you get 18mm effective area with a 20mm mirror??
To me, it souns impossible.. When mirror angle 45defelree, its effective size was times by 0.707 time
Plus 1mm on thr mount, I believe you can get about 12mm effective size. Correct me if I am wrong.

Marco

[Techgraphix]

My beam expander is after the last mirror, so the beam enters the first expanderlens as 5mm. At some distance (I can't remember exactly but it was about 30mm?) the beam hits the second expanderlens and right after that it enters the focal lens.
I had to turn out the tube to place some thin rubber O-rings in which the lenses rest. The diameter of the hole is now 19.2 mm.
Lenses can have some spherical aberration, may be my lens does have plenty (although it is a HQ lens) but the results count.
Somewhere there is a middle between that aberration and the usable diameter of the lens.
A beam twice the diameter should give half the focused spotsize (theoretically) and about 4.5 times more energy-density (Watt/mm^2)
By placing two lenses more (the beamexpander) you will also loose some power... Although I expected to have some advantage of the increased energy-density (less power needed, I hoped) I didn't notice anything ..
Maybe I have to bring it back to 2-2.5X
Anyway, here a few photo's of how i made it.. (apologies for my humble photographic skills)
The lensholder of the small lens, that fits tight in the tube and can be pressed at position

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7.JPG (74.15 KiB) Viewed 4274 times

Lensholder in tube:

1.JPG (68.41 KiB) Viewed 4274 times

With second Expanderlens and rubber O-ring:

8.JPG (66.5 KiB) Viewed 4274 times

With Focal-lens and nut

9.JPG (60.26 KiB) Viewed 4274 times

Looking through the expander:

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