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View Full Version : laser not cutting cleanly in plastic/pvc anymore



Todd Mueller
07-28-2017, 11:40 AM
I have a chinese 60 watt machine that is just over a year old. until about 3 weeks ago, it has cut perfectly. I use it on average no more than 10 hours a week, never going over about 17ma of power, in which my machine has that meter built in.
the lenses are clean and the alignment of the lasers is good, they hit the same spot no matter what part of the cutting field i am on, it is a 600x400mm size machine. the laser hits the center of each mirror.

I do cut pvc with my machine and clean it after every use and I am well aware of the safety issues with pvc. I have a filtration system specifically for pvc cutting.

the material i cut is less than 2mm thick.

my first ideas are possibly the power supply acting up, the cuts are now just not clean, they leave little bits of material in the cut area that make it harder to remove the cut out pieces, and it didnt use to do this. kind of raspy looking, i guess is how i could explain it. the power supply is rusty somewhat on the outside from the pvc gases and such, but i have no idea what it would look like internally. it does seem like maybe the laser is a little weaker than when i first got it, but it may just be because of the "not clean" cut

2nd idea is the tube, but knowing that they typically would last much longer, im not sure on this. my cutting does do a lot of intricate designs, so lots and lots of laser on/off during my cuts, but other than that, the tube doesnt seem to have tons of hours on it compared to what i think it probably should last

3rd idea is the focusing lens, although i clean it regularly and have good air assist, i can visually see the coating on it as being kind of splotchy, not scratched or dirty, just discolored kind of like looking at water colors.

all rails are clean and sliding nicely

I am trying to think of some things to test to rule some things out, like maybe cutting some paper or cardboard

Robert Bonenfant
07-28-2017, 11:55 AM
Try to switch out the focusing lens first - We switch our lens and mirrors out about every three months, we use our machines over 50 hours a week. Any imperfection with your focus lens or mirrors will give you issues.

Have you tried to increase the power and see if it helps ?? When one of our tubes was on its way out we had to increase the power 20% above our other machines to get the same result - Needless to say we knew something was wrong.

Bill George
07-28-2017, 12:16 PM
PVC fumes cause corrosion on connections and wiring you can not clean. Also very possible your mirror surfaces and optics have been compromised.

Todd Mueller
07-28-2017, 3:32 PM
Try to switch out the focusing lens first - We switch our lens and mirrors out about every three months, we use our machines over 50 hours a week. Any imperfection with your focus lens or mirrors will give you issues.

Have you tried to increase the power and see if it helps ?? When one of our tubes was on its way out we had to increase the power 20% above our other machines to get the same result - Needless to say we knew something was wrong.

Thank you, for the advice, I will try the focusing lens. Can you tell me what your procedure is for cleaning them, I use regular qtips, with rubbing alcohol, one side wet to swirl around and clean it, then the dry side to dry it off and get smudge/swirl marks off.

Kev Williams
07-28-2017, 5:35 PM
I've engraved several thousand pvc trays in my LS900, I can attest that IF you're sucking up the fumes well, the detrimental effects are minimal. The worst that's happened to my machine is the lens housing darkened due to it passing thru the smoke. Another issue Bill brought up, mirrors, especially over the lens, the reflective surface can be corroded.

That said-- if your power supply is rusting, you're not getting all the smoke out, that needs to be addressed...

Bill George
07-28-2017, 5:46 PM
Once again the rust on your power supply is a good indication of no matter how good your exhaust system is working or you think it is anyway, its not. The number one rule for lasers is no PVC unless you consider your machine and lungs throw away items.

Dave Sheldrake
07-29-2017, 6:19 AM
One of my machines was designed and built for PVC cutting, the extraction system alone is the size of a medium sized car. the entire thing bears no resemblance to a normal laser in any way.

The laser head is totally different and uses a pressurised lens chamber to avoid damage to the AR coatings on the optics other than the final window that excludes the gas. It's inspected and tested every 3 months by the HSE who monitor fume levels and write out test results that I have to abide by.

Everything in it is either sealed or plastic coated to prevent corrosion.

If ANY part of the machine is being damaged by the gasses then your extraction system is suspect at best.

Wilbur Harris
07-29-2017, 10:34 PM
Replace the lenses and mirrors if they won't clean up pretty good. Increase the power to see if that helps. If increasing the power makes it do what it used to do start working toward a new tube.

Sam Gardner
07-31-2017, 2:23 AM
How about some pics Dave?

Dave Sheldrake
07-31-2017, 9:42 AM
I'll get some done soon as I get 30 seconds Sam, it's chaos here at the momennt (I'm working 18 hour days ,7 days a week) :(