I guys I’m having a problem with my k40 I can’t make it cut trough a cardboard it’s like 2 mm any ideas?
wrong video 
this is couche paper 130grs
Your mirrors are most likely out of adjustment if you can’t cut paper or cardboard. This is a great article explaining how to adjust them
http://www.floatingwombat.me.uk/wordpress/wp-content/uploads/2015/02/K40-Alignment-Instructions.pdf
Alternatively to @funinthefalls 's suggestion, your lens could be upside down. A lot of us had it ship upside down & it would mark like yours is, but very difficult to cut. When swapped over it cut like hot knife through butter for me.
when you say lens it’s located where it’s the Last miror?
It is in the laser head (the part that moves back and forth with the laser beam exiting it to the work piece. It unscrews, exposing the lens.Carefully clean it with a soft cloth an isopropyl alcohol, the flip it 180 degrees and put it back in the head and screw it back closed.
I wear nitrile gloves to keep the lenses oil free, and clean them with MG 810-15 Chamois Swabs. Amazed at how much gunk those swabs lift off the lenses.
How can you tell if the lense is upside down? I put the curved part down pointing to the workpiece?
@Christoph_E according to most peoples opinions (and i say opinion because it does just seem to be peoples opinions…) curve side suppose to point towards laser source.
i tried several line tests tonight with the lens flipped either way, and achieved exact same focus distance, sharpness of the point, seems like same cut depth too, no matter which way it was flipped… although some people report better results with it flipped one way, and others report better results with it flipped the other way… so go figure
so im personally going with curve side facing up (away from table) because most people seem to reiterate this.
Thanks for your Answer. Maybe i’ll try to switch it too.
Imho that’s stuff that really should be written in a Manual. The missing manual yet is the biggest Problem i got with that machine/software. ^^
What settings do you use for trying to cut that Cardboard Cesar?
A lens with one convex side and one flat side is called a plano-convex lens. You will get focusing in either orientation but it is much sharper with the convex (curved side) up (toward the laser). See the bottom diagram here. http://folk.uio.no/walmann/Publications/Master/node8.html
For a properly made lens having the flat side toward the laser will result in longitudinal spherical aberration (bigger spot).
i cut 2 lines across material on a slope, with lens facing each way.
I can’t tell any difference.
at least, with my eyes anyway, maybe there is the slightest of slight differences but nothing major like everyone says there should be?
It looks to me like the line is sharper and more burn with the curved side up. All this is really dependent on the a lens being properly made and that your mirrors are all properly aligned. If the beam isn’t hitting the center of the lens it’s not going to focus well either way.
@Nedman thanks, good point on the alignment. something I never got 100%, just ‘close enough’ and gave up.
so what you’re saying could make sense as to why there isn’t as much a difference as there should be.
hi guys I already flipped the lens and looks like it have a deeper cut I’m going to made another alignment, thanks for the advice 
Make sure you are the correct distance away for your lens. Stock is approximately 50 mm.