Hello,
I have rebuilt my k40, new tube, LPS, mirrors, and lens.
After replacing the tube first cut was amazing 10 speed, 25% cutting through easily. The next day it started cutting, worse, and at the end of the day it stopped cutting through.
Also there is small bubbles in tube, after a bit of running its turn into bigger bubbles.
I clean mirrors and everything works fine. Need to upgrade exhaust system
Sorry for creating this post for now 
please close or delete
No apologies needed!
Next person who comes along searching for reasons for reduced cutting performance can find this post. 
No problem, we have all been there at some point.
The topline advice we always give anyone we see a loss in power is to check the alignment and make sure their optics are clean. That usually solves 90% of the problems.
You probably should get rid of the bubbles.
Did you install the tube with the exit tube upward???
water exit tubes are at ~60 degrees, but also I lowered standard water pump ~1.5m bellow laser, so maybe its not enough water pressure?
Is the end of the water return hose under the surface of the water in your bucket or reservoir?
Same problem here…
First cut test where 40% at 10mm/s and it was nice. I have been cutting all day with this settings. Water is perfect (max 24ºC)
Now I have to make 2 passes to cut, and getting worse.
I did clean the mirror and the lens under the head: I use a cotton stick and isopropyl alcohol
Also, did a lens aligment test and it was fine.
I dont know what else do/check
Tomorrow will be another day, no I am really tired.
Answer to myselft (and other idiots like me):
To clean the lenses is to disasemble it and clean it on BOTH sides.
Idiot of me was cleaning only the outside.
Note 2: after disasembling it, make a alignment test, just for “if…”
Thanks for following up with the answer! It’s kind to the next person who finds the same symptom and ends up looking here!
(No idiots here, we’re all learning together!)
