Why is my laser cutting 2 lines at once?

[Michael Stankiewicz]

I'm new to this forum - hoping someone has experience with this problem

We have a Kern 150 watt - a beautiful machine - no problems
And a Hurricane the last one Hurricane Lasers sold before they went belly up - this machine is my problem child

Came in this morning and looked at the reports from last night - no production
Upon examining the .177 red acrylic in the trash - the laser didn't cut through completely and there were etch / cut line bordering the parts on the sheet. The etch marks are approx. 1/8" below the actual cut line running along the X-axis only. The "etch" marks run from .005" - .040" deep and are intermittent.

Checked all mirrors for debris or crack - nothing found.
Checked mirror alignment - all good
Checked lens condition and orientation - good
I also ran a test to be sure the machine wasn't cutting twice - it's not - it's cutting 2 line intermittently at the same time

The only thing I noticed was the focus tube seems to have some play in it - up to 1/8" at the nozzle end.
Currently waiting to get on the Kern to create parts for a "lens tube square / focus tool" to ensure the tube will be perpendicular to the laser bed when it's focused.

Any ideas?
Thanks
Mike

[Matt Turner (physics)]

Does the laser have an air assist? I recently had something happen like this with our Kern. The cutting head came a bit loose from the linear bearing, and the air assist would intermittently lift the nozzle, causing a shadow etch below the cut line.

[George M. Perzel]

Hi Mike;
Check for a loose lens
Check for a cracked lens or has a spot on it which is deflecting the beam
Check for loose head or belt
Insure head is perpendicular to table
Check for loose mirror
If none of these work, send me the Kern unit and I will send you a GCC Mercury1!!
good luck
Best Regards
,George
Laserarts

[Scott Shepherd]

He doesn't have a problem with the Kern, he has a problem with the Chinese hurricane one.

[George M. Perzel]

Scott;
Yea- I know
Best Regards,
George
Laserarts

[Dan Hintz]

If it's physically burning two lines at the same time, it's an optics issue... not necessarily bad optics, but an optics issue, nonetheless. If alignment has been checked, it's a loose lens/mirror (or mount) somewhere along the path. A continues double line (i.e., two parallel lines that cut in/out at the same time) say it's a double beam... the beam is not hitting the final lens in the center. If it's one line on, other line off, then swapping back and forth, it's a loose something or other vibrating back and forth.

[Michael Stankiewicz]

Thanks for everyone's input.

After combing the web for a few hours I applied bits and pieces of advice I found and created a plan that seems to have corrected the issue.
Some links are listed below.

http://hiq.linde-gas.com/internet.lg.hiq.global/en/images/Linde%20Laser%20Cutting%20Advice899_90085.pdf

http://www.repairfaq.org/sam/laserco2.htm#co2pcls

http://www.hasary.com/service/2.html


Built a fixture that ensures that the focus tube is perpendicular to the stock when its locked in place - this check will become part of the SOP
Built an adjustable nozzle that allows the standoff distance between the aperture and stock to be changed as needed and the aperture is also adjustable in diameter.

Thanks
Mike

[Bill George]

If your talking about the Chinese laser? I think the focus tube only has two screws to hold it in place and its a little loose anyway, at least on mine. Just make the opening a little larger on the cone so the beam will exit without bouncing off the tube inside. Suggested by someone on here.