K40n Laser lens problems

[maria galligan]

It's Maria here. I have a problem with the back laser lens. It has very bad burn mark on it, it almost looks like the laser is putting a hole in it. Is this normal? How do I stop it from happening again? And can I use the other side of the lens? And are the cheap lenses any good or should we buy better quality lenses? Any help will be appreciated as I'm new to Lasers and am still finding my way around the machine. Thanks:confused:

[Dan Hintz]

You can't use the back of a lens since the beam must pass through it... if one side is toast, the entire thing is toast. Even the inexpensive lenses ($15) are quite adequate for our needs. It could be a fluke that it happened, but make sure the mount area stays clean of debris (this includes smoke during operation)... get into a rigorous cleaning schedule for your entire machine.

[maria galligan]

This sounds stupid I'm sure but I thought that it was like a mirror and the beam was reflected off the lens, but your saying it passes through it. I'm sorry we are new to laser engraving. We had so much trouble getting the drivers to work that we were so happy to finally start the machine but it only lasted one day and the results were not good. We engraved names on mdf 5mm board and it engraved dark to light to the point the last letters were barley visible.So I assumed the beam needed setting. I only noticed the mirror when I tried to set the beam. I know the beam is hitting the middle because that is were the mark or pit is. How long can we expect to get out of the lenses? I'm now thinking the lens must of been like that when we got it. Because it only worked for max 1hr. Thanks Maria

[Dan Hintz]

Do you have a dust collector attached to your bed? Wood is one of the worst materials when it comes to fumes... heavy particulate matter that will gladly stick to lenses and mirrors. If you're not running dust collection, I would say your first attempts at getting the machine running were what killed it.

Mirrors and lenses are two different things. Lenses have a proper orientation (though will often work in a reduced fashion in the improper orientation), and mirrors are one sides (the reflecting surface is right at the surface, not behind the glass, like on your bathroom mirror). Take care in cleaning both as they can be scratched.

[maria galligan]

Can you give me some advice on a reasonably good cheap lens for a cheapo Chinese k40 laser engraver? To be honest I like the sound of $15 lenses who sells them at that price?