Cracked Lens and New lens problems

Looking for assistance with swapping out a cracked lens (I’ve been using lasers for 7 year and have never seen a cracked focal lens).

Installed a replacement lens that came with the laser but now the laser is spread out huge when I cut a shape.

Running Zing CNC 9060 80W Ruida 644XG controller.

That lens is filthy. I’m not surprised it cracked, all that trash must have absorbed a tremendous amount of energy.
Did you focus it after you replaced it?

I had just cleaned it two days prior, but we have been doing a bunch of wood items. As for focusing, we did use our focus jig to set it to the correct height, but the laser beam is still very wide no matter what distance we have tried away from the surface. We also tested the mirrors as well for alignment and everything is fine.

Sure it has the same focal length?

Don’t trust your jig, try a focus test via the ramp method

I had a vendor ship me a 2" lens, turned out it was actually a 1.5"
Thought I was going mad trying to get the thing to cut or engrave, I did refine a whole bunch of other things on the machine as a side benefit :wink:

Take the lens out and position yourself under an overhead light with a ruler. Hold the ruler vertical, resting the end of it on a surface. Then hold the lens perpendicular to the over head light and beside the ruler. Center the focused image as best you can that appears on the surface and then move it up and down, it will be pretty obvious when it is roughly in focus, check where the bottom of the lens is according to the ruler.

As these lenses are normally in 1/2" increments of focus it’s pretty easy to see where it lands. This confirmed for me what I had suspected with the lens I was shipped. My focus area was up inside the nozzle with the 1.5" one installed :slightly_frowning_face:

I had a similar experience, my K40D came with a 1.5" focal length lens and I was completely expecting a 2" focal length. New machine wasn’t cutting nearly as deep as it was supposed to… :slight_smile:

Hi folks. I did the ramp test and also tested the focal length with a light and a ruler. Looks like it could be a 2" lens as opposed to a 1.5 that it was labelled as. I did a 10, 20 and then 30% power ramp test. 80W laser. What could be making the beam be so wide? I double checked that then lens in in correctly already. Mirrors are all aligned with a masking tape test.

Also did a tape test with the cone off at the bottom of the 45 degree mirror above the bed. Almost in the middle. Thought that the wide beam was a result of not hitting the middle of the lens but it’s pretty close. IMG_8384|375x500

I thought so, but here it my ramp test. 10, 20 and 30% power.

I still believe you don’t have the correct lens.
There are some cheap options on Amazon, worth a try?

Also make sure it isn’t turned upside down. (Hope I didn’t miss it if someone already suggested that. I was scanning quickly.)

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Also, be sure to have air assist on to prevent soot from coming into the cone from the bottom side. (I bet you already are using air assist). WHICH brings me to my next comment / opportunity to share an idea I have with you.

I am constantly annoyed with soot / contamination of fumes coming into my lens holder from the top. I’ve been considering designing / pluming my air assist into the upper part of the lens as well to keep positive pressure in the top side to prevent soot from collecting on the upper side of the lens. Maybe an idea.

Upside down lens was my first thought, too.

Ditto, I am considering drilling a hole into the laser head body and splitting off my air hose to pressure it as well.

Cloudray and other manufacturers sell a silicone o ring that goes on top of the lens to help seal it and prevent the air assist from pulling smoke in through the top, if that helps.

I already use a nitrile O ring on both sides of my lens. I have incredibly effective fume extraction as well. However, there is always the possibility that soot or other debris will end up entering into the top of the lens holder cone (where the laser beam enters). So to minimize this, I am going to positively (yet just slightly) pressurize the upper side of the lens holder as well.