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Frank Corker
12-05-2006, 10:17 AM
Has anyone got or have they used the new 1.5 lens that was introduced. Also for those who have the Legend EXT, what do you use yours for?

Wil Lambert
12-05-2006, 10:29 AM
We use the stock 2" lens on our EXT36. I do do a lot of photo engraving and have never had a problem with the 2" lens. The only other lens I would probably buy is the 4" for cutting thick materials.

Wil

Dave Fifield
12-05-2006, 4:27 PM
Hi Frank, I just received my new 36EXT with both the optional 1.5" and 4" lenses last week. The 2" lens is a good-compromise-all-purpose lens IMO and is what I have put up with until now (in my previously owned 24TT and Mini 24 machines). I have the 1.5" lens fitted right now, and will probably use it for the majority of my work, which is cutting veneers for marquetry ("laser marquetry").

The 1.5" lens has a very small spot size. I don't know exactly what it is, but my kerf-filling tests over the past weekend seem to suggest that is it in the region of 0.0015" diameter, or, about half the spot size using the 2" lens. As they say back there in Blighty (I'm an ex-pat Brit) "you don't get ought for nought", so you pay for the small spot size in that the focussing if much tighter using the 1.5" lens. For 1/32" thick veneer, this is not a problem at all.

The 4" lens with its much longer focal length has a much more vertical kerf that makes it good for cutting thicker stock with a nice straight edge. You pay for the longer useful focussing height by having to put up with a larger spot size.

Hope this helps.

Cheers,
:Dave F.

Rodne Gold
12-05-2006, 6:51 PM
Dont waste money on a 1.5" lens unless you need it , its a specialised lens and its depth of focus is very small , it's smaller spot size wont "double" your power , there are no free lunches in lasering.
Apart from anything else , your head to object clearance is less and the lens assembly is more prone to smoke and dust contamination. Only really useful for real thin stuff thats dead flat. As to "finer" detail engraving , well its not just the spot size that determines how good that will be , if your motion system is not 100% with zero backlash or has the minutest amount of slop , its not that effective anyway. Large areas of fill are also a problem in that you have to use a high dpi which puts a lot of heat into the material to get a smooth surface - engraving time rises a LOT and some materials heat warp.
However there is one advantage , at least for me , in that my 30w laser can mark stainless using vector engraving thru a 1.5" lens (albeit it's extremely slow)
As to the 4" , well that is only really useful for thick stuff IF you have the power to compensate for the greater spot size.
Bear in mind that the spot is sort of circular and doubling the spot size in effect more than doubles the area , for example a 2mm spot has an area of Pi r2 , ie 3.14 mm squared , a 4mm spot size has an area of 12,5 mm2
There has to be a certain power density to promote the thermal shock that starts the vaporisation of the material , and one would have to put a LOT more power into an area 4x another to maintain this power density (watts per sq mm )
For example if your 30w laser can just cut 8mm with a 2" lens , its probably not going to cut 12mm with a 4" as you wont have enough power. A 100 w laser will not have this problem.

Frank Corker
12-05-2006, 9:27 PM
Thanks for the replies to all of you, that's pretty much me decided then, I don't need it. It was going to be hard enough me justifying the scary price of 295 + VAT =346.62 - or - $683.88US

I think I can live without that!

Dave Fifield
12-05-2006, 10:16 PM
Good points Rodne. I do have to add though, that in the short time I have owned my new laser, the kerf-adjusted laser-cut veneer marquetry tests that I have done show a marked improvement in the accuracy and fit of the pieces using the 1.5" lens vs. the 2" lens. For me and my needs (vector cutting wood veneer, not engraving it), the extra cost is worth it apparently.

Rodne - I'd be interested to know what power/speed/frequency settings you use to mark stainless steel. I'd like to give it a go.

BTW Frank, you guys are getting ripped in the UK. The optional lenses are $350 each here (177.39 UKP at the exchange rate you quote above).

Cheers,
:Dave F.

Rodne Gold
12-06-2006, 1:41 AM
Dave , you for your application the 1.5" lens is ideal , especially the fact that you do get a higher power density at the cut and thus your edges should show a lot less charring/dicolouration too.
I think the SS marking settings are something like 100% power and 0.3%-0.5% speed. Our machine wont do raster at that speed , only veector. You can actually feel the "engraving" into the metal.

Frank Corker
12-06-2006, 8:01 AM
BTW Frank, you guys are getting ripped in the UK. The optional lenses are $350 each here (177.39 UKP at the exchange rate you quote above)


Thanks Dave, that's comforting. :( You should see the price of the machines!



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