ZnSe Lenses needed or not ???

[zoefie]

Hi all,

I'm looking for a couple of ZnSe lenses for my 60watt co2 laser.

My machine (lg1200) is equipped with the standard 20mm, FL= 2 inch lens, and is performing quite well with it.

I hope that with a FL=1 inch lens it will be possible to engrave in more detail.
and with a FL=3 or 4 inch it would cut better in thick materials like acrylic 12mm and mdf 12mm

Is there really a big difference in performance between the different focal length's in the area of engraving and cutting?
Or are the differences minimal?


Also i'm looking for a good shop where i can buy these lenses at a fair price
On ebay for example you find lenses from about 50 USD up to 200USD each.

Does the quality of the engraving/cutting really depend on the quality/price of these lenses, or is it more something of the time the lenses will keep doing there job before they are defective?

Best regards,

Ferry.......

[lrob]

Good questions.

I would be interested in some good advise to your questions also.

[Tweakie]

Hi Guys,

Just a couple of things to consider;

A longer focal distance lens enables a greater depth of cut (longer focal length) but has a larger spot size (width of kerf).

A shorter focal distance lens only allows a smaller depth of cut but has a much smaller spot size.

When cutting 10mm acrylic the short FD lens produces more barreling on the edges than a long FD lens but (from my experience so far) a better quality edge.

Tweakie.

[lrob]

Tweakie

Thanks for the excellant diagram. Most helpful.

Should a longer Focal Lens also yield a faster speed and or less charring when cutting wood?

Larry

[Tweakie]

Larry,

Should a longer Focal Lens also yield a faster speed and or less charring when cutting wood?

Don't know about faster speed. The feedrate and laser power setting are so closely related that it is probably just the material being cut that determines the speed (acrylic likes being cut slow and wood likes being cut quick).
As for charring, I think that using Nitrogen as the assist gas is perhaps the only way to prevent it. (haven't had a chance to try it yet though).

Tweakie.

[zoefie]

Tweakie,

Can you give me an estimate for the difference in spot-size between a 1" and 2" lens ?
does it really make a big difference in engraving quality ?

[Litografa]

I can't provide exact numbers, but can say that engraving quality between 1,5 and 2" lenses are really big. Engraving lines with 1.5" lens much thinner.

[zoefie]

Ok, thats great to hear!

Do you have experience with the different price's they ask for ZnSe lenses.

For example i need a 20mm lens FL=1" i've got price's between 45$ and well over 180$ both of them suitable for CO2 laser.

I'm trying to understand what the reason is for this big price difference. Is it just the amount of profit a shop is making, or is the a real difference in quality or lifespan of the lenses?

[Litografa]

We are selling only original GCC lens. For example our sales price is 190 Euro. But I know customers who use this lens for 4-6 years working at least 3 hours per day/ 6 days per week.
So really price depend from quality. I am personally do not believe "quality optics made in China". Good optics are made in Singapore, USA, Germany.