Head questions for the experts

After upgrading my mirrors and doing an alignment that included getting the beam in the center of the head lens my K40 is working SO much better than stock. That got me thinking that the final step to optimizing cutting would be a larger focus lens and a height adjustable head like my large format laser has. While the depth of focus might allow decent cutting of thicker material it just seems obvious the best results will come from the best focus. Yet I only see one K40 adjustable height head design being offered and I wonder if it will even work with a standard K40(engraver) bed heights.
So the question: is it worth $30 for an adjustable head and similar for a new 18mm lens? One gains air assist doing that too. Obviously an adjustable bed is an option but rather more expensive even as a DIY and does not address if a 18mm lens is better.

99% of the people in order to get optimum focus will adjust the height of the object they are working on rather than adjust the height the focus lens. The more you futz with the focus lens the more chance there is to mess up the rest of the optics.

Also do a quick search on lens focus and density. There is a lot of information already posted here.

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With a lens height adjustment you will end up with less working height unless you cut out the bottom of the laser. If you are only working with thin materials then it might be worthwhile.

I think there are two 3d printable adjustable height lens designs on thingiverse and a third that someone is printing (the print quality looks, serviceable but not fantastic) and selling on fb.

And then there’s the aluminum telescoping head sold by cloudray and various chinese vendors. It needs to be mounted about 9mm lower so there are 3d printable mounts for it. Or you can mount the tube and mirrors 9mm higher, etc. It’s said to be better if you bore out the air nozzle a little and install an o-ring between the lens and the part that holds the lens in place.

I’ve used the fullspectrum hobby system. Using a precision machined spacer to set the lens at the appropriate height for the material was for sure convenient. I don’t doubt that it’s better if you spend less time fiddling with the laser head.

I ordered the aluminum telescopic head along with a lens that has a 38.1mm focal length for some more flexibility. I do have dreams of a motorized Z table as well.

Thanks guys, I was thinking someone surely had tried the adjustable head and would know exactly how much room there was.
I’m not interest in a printed or otherwise plastic head… And I’ve seen pics that at least some K40 came with an adjustable head which does not seem to be available as a seperate item.

But after doing the suggest search for focus and density, I think I will order the head and see if it will support(not too long of an air assist) a 38mm focal length lens. That will give me the height of a new bed. As the bulk of my cutting is 3mm and under it seems 38mm would yield the smallest kerf and greatest cutting power for difficult materials like fiberglass.
As to the Cloudray, I have the same thing from another supplier on a 1600x1200 frame and its huge, not what I’d consider appropriate for the K40

Life is funny… having made the decision to try the adjustable head, the very next search for a source got me this image which has exactly what I need to know to measure the fitment. I looked at dozens of sellers for this head and none had any hard info, so this is a super find. I hope it helps anyone else who is considering options.https://i.imgur.com/p8w9XBX.jpg
This seems to come out that the head minimum length from mount plate to nozzle tip is about 2" and just under 3" max but the retainer screw position will cut that down by 8-10mm at a guess. With the stock work surface I have 2.75" of room for 3mm material.

Then the only unknown is how high the lens mount position is- in my case if it is too high for a 38mm FL lens I can machine it deeper and use a spacer ring under the retainer.
I will try to remember to report back how it goes.

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Very old design there

but the main things is plastic burn. If you can go for aluminium don’t hesitated.

Pleased shared your experience with 38 mm lens. Some have said here they have deeper cut with it.