yes, it’s a kind of fine tuning but also part of the test itself. “Usually” as fast as possible with the least necessary power, it gives, in my experience, the cleanest cuts.
Pine “always” cheats "a little, it’s so nice easy to cut, no glue no pockets only nails once in a while 
I have just the opposite view, the highest power at whatever speed it takes…
Interesting…
… if you reach the same goal then that’s fine 
Tried both ways. Seem to have cleaner cuts with a slower speed and higher power. This is for mdf or plywood…
Everything is relative, it is possible that the curves meet each other, where the best cut can be achieved, at roughly the same settings.
But with thick materials, it does not help to pump lots of energy into the cut, if it does not reach the bottom, then the sides just turn black due to the heat.
Agreed… I use a 4" lens when I cut, but nothing like the thickness that you are dealing with…
I do not think the nominal 10 watts make a huge difference in the cutting options. With my K40 (real) 40Watt machine I could also cut 15mm acrylic, not particularly nice or fast but it is possible. And when we run into bad plywood, power is almost second-rate priority, you get through a little better but the glue in the pockets explodes and everything is sooty.
4 "- what good or bad experiences do you have with this focal length?
I set it up, generally for cutting, so the nozzle is very close to the material. Has a wide kerf but deep penetration. It’s different. In fact, I re-arranged my ‘materials library’ so all the main entries are under the lens type. I’ve found so much of a difference between the same material and different lenses that I do better separating them into ‘lens’ groups.
I tend to use the compound for detail engraving, 2" for general engraving/cutting and the 4" for cutting thick materials. I have configured the 4" and used it on some mirror material I had, as the coating went everywhere and coated my lens on the first attempt.
Really just a nozzle adjustment…
I’m still learning about this stuff also…
My lens are 18mm, don’t know if that will make it harder for me make something work.
Where did you buy the extension lens tube?
I am still experimenting. Notice jack and Bern, you are using 4” mine is 3”.
I am forever grateful for your information.
Will keep you posted with what I determine or find out.
Anytime you change a lense focal length you have to have the correct tube… you cant just put any lense in… for example my Omtech 70 watt is 2 in focal…. I can’t just put a longer or even shorter focal length lense… that’s why if you order from APC they sell them in sets…. If you got from Amazon you need to return them or buy the correct tube that accommodates that focal length… if your trying to change focal distance with your stock 2 in lense it will never work correctly
Thank you Michael
You need to fill me in on APC
I have no idea who you are referencing
American Phototonics makes some of the best mirrors and lenses… customer support is great
My Omtech 60W CO2 uses D18mm lens. I have a D18mm, 76.2mm lens also a FL 63.5mm lens.
I have scoured the companies to see if any of them have D18mm, 76.2mm lens tubes. NONE
I find D20mm, 63.5mm lens tubes, no D18mm for the 63.5mm FL
Hi Marion, Ø18 lens only fits in the original OMT nozzle head, so if you want to use their extension tube you need to buy Ø20 lens. But still I have found an option with soft washers to mount an Ø18 in my extension 
I’ve traded with Cloudray, through Amazon. Because there is some bureaucratic hassle with tax and duty, Amazon is for me the best option, they “fix” all this. The shipping cost and tax is a bit high but I myself can not cut these pieces out of wood
Nb. Cloudray`s customer service is very responsive and friendly (towards me), they regretted that they could not get or make a Ø22x1-22x1 adapter and sent me 2 intermediate ring for free, the one I now use as a “temporary” connection.
I plan on cutting one extension in half and making a connection option with my existing nozzle holder, the solution I am experimenting with now is way too long.
It’s Jack who has a 4 “lens, I only have 2” and a 3 “lenses. But as I said before, my 3” is primarily intended for straight cuts in foam and I could not really see the completely wild differences in connection with cutting in wood and acrylic.
I think the only right way is to buy and install a suitable new nozzle holder - complete. I still want it from Russ, but the need right now is not as great as the desire itself, for me.
If I manage to find a lathe and I can make a usable adapter I will let you know.
That’s absolutely correct, everything changes when playing with lenses and their focus distance. Therefore, I have also done my preparatory work to find out (theoretically) whether the laser beam has free passage through the nozzle and what distance from the nozzle to the processing material I can achieve.
The error in my calculations / experiments of 2.5mm in the focus distance, is due to my slightly lenient assumption of the raw laser beam without lens.
Michael,
I have contacted APC. They show a kit that looks as though it has the extension tube I need. Do you know if the tube in their depiction of the kit, on the left side of box, has a 20mm insertion end to it? I don’t quite get why they glue the lens in the tube. I understand they are actually using a D20mm lens. As long as it works in my Omtech 60W I don’t care.
Bernd,
Have contacted APC. They have am extension tube I think will fit the Omtech. When I get further info I will let you know.
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If I recall, I didn’t order a 1.5" lens, that came with the machine. It will fit into the C series tubes. I still run it and just put an o-ring in there. Narrows the target area from m3, but if you are that far off doubt it will make a lot of difference.
The diameter difference is only a millimeter a side or 1/25th of an inch.
Mine started out and I guess still, is an OMTech 50 watt ‘China Blue’
Contact Russ if you are interested in his head design. I think it’s better than sliced bread…
Bernd and Michael,
I received a nozzle lens combination from APC which I determined from their website was what I needed at this time. I was afraid what I ordered may not fit in my Omtech since I received a message from them before I ordered that they didn’t sell the item I wanted as a single item, only in a kit. That wasn’t true since I have the item in my shop now.
Bernd I think you would be happy with this setup although I have no idea what it would cost shipping wise to get to you from Florida.
Only thing I am confused about? They glue the lens into the lens tube. Hmmm
When I have a photo of the unit I will post.
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