Laser Stops Cutting Mid Cut

[Travis Emmel]

Hi,
I'm looking for a bit of help chasing down a problem with my laser dying out during a cut. I have a "60W" Chinese laser and tried running a job this evening. About 30 seconds in, the laser's cutting ability rapidly fades, the cut depth tapers off and then stops penetrating the material altogether. If I shut things down, wait a couple of minutes and restart the job, it seems to fail consistently at the same point in the toolpath. I'm running at 65% which equates to ~18mA on my meter. Not sure it matters, but for the sake of completeness, I'm using a Ruida controller and Lightburn. I've maybe run 20-30 jobs on the machine since I bought it, so the tube has seen very few hours under my watch.

Things I know:
Alignment is good - I can pulse anywhere on the bed and get a mark on my workpiece.
Coolant temp is at 19deg C, using a chiller. No air bubbles.
If I pause the job, wait 10-15 seconds and resume the job it will cut for a few seconds and then die out again.
The tube is glowing the entire time, pinkish colored beam.

Any help or troubleshooting advice is much appreciated!

[Gene Uselman]

Is your bed parallel to the gantry... IE- the focus is not changing as it moves across the bed? Or possibly the alignment of the 2nd mirror is not centered on the cutting head mirror and is far enough out to clip some of the laser beam as the head moves across the gantry..

[Travis Emmel]

Is your bed parallel to the gantry... IE- the focus is not changing as it moves across the bed? Or possibly the alignment of the 2nd mirror is not centered on the cutting head mirror and is far enough out to clip some of the laser beam as the head moves across the gantry..

Hi, Gene.
Thanks for checking in. I've confirmed that the head and bed are parallel. This phenomenon happens anywhere on the bed, regardless of location. It seems more of a time issue (i.e. after 30secs, it cuts out) which leads me to believe [current theory] that maybe something in the power supply is heating up (loose wire?) and either shorting or breaking contact. I'm going to take a closer look at the wiring today.

[Travis Emmel]

I *think* I found the problem. Looks like my lens has a hotspot on it. I'm guessing this is causing enough heat buildup to change the optics just enough to affect the beam getting to the workpiece. Gonna try swapping in a new lens and see what that does for me.

[Travis Emmel]

Success! Turns out the lens was knackered. New lens has everything back online again and is cutting like a dream. Not surprisingly, it feels like I picked up a bit of power in the process, as well.

Pic of the old lens:

PXL_20201018_172318939~2.jpg

[Gene Uselman]

Good for you- as complicated these machines seem when we first start working with them... they come down to a very few parts that affect the cutting and applying a bit of thought to how the beam does the cutting can really narrow things down.