So it seems I will need to replace my tube, I can barely engrave let alone cut anything now. Mirrors are clean and aligned, lens is brand new, so I am pretty sure it is the tube. Any body have any ideas where best to buy either a 40w or maybe a 50w (with a case extension). I would like it to ship from North America if possible unless the overseas price + shipping is too good to pass up.
I got one from http://automationtechnologiesinc.com and it was much nicer than the tube in my k40. Seemed like it had more power too.
I tried the lens upside down and downside up…no real change.
Was it working fine before you changed the lens/head? Have you tried it with the original hardware?
Also did you actually find the focal length? Try the ‘ramp test’. a piece of material on a slanted angle, lowest point and the floor, highest point just below the head (so you don’t hit anything), burn a single line horizontally across it, starting about midway to the highest point and measure the thinnest point to your head.
Might be a dud tube, apparently if it works for more than a few weeks it usually lasts a while. 
I am pretty sure I have the focal length correct, from bottom of nozzle to underside of lens was 28 mm leaving 22.8mm from tip of nozzle to work piece. I’ll run a ramp test just to be sure.
At a guess you’re 8mm out. Anyway a ramp test will tell you what it should be. Hope it saves you the cost of a new tube!
Laser depot is where I bought mine…275.00. But it comes with a year warranty…it’s I puri which is I good brand.
Actually just installed one of mine and did a ramp test and you’re pretty close, mine came in at 24.5mm, so probably is your tube if everything else is clean/aligned.