Power lowering during long cut jobs

[Giacomo Cheslaghi]

Hi everybody,

I recently received an order for some plexiglass keychains I designed, (100) and I was so happy since it's one of my first jobs, so I setup my file, and prepare to cut the first 30 of them from the first sheet.
I set the recommended speed and power, and since I have an Epilog Zing with just 30W of power, prepare for a LONG wait (raster+vector cut=more then 20 minutes).
In the raster part everything goes smooth, then it starts to cut, and after some time (30% of the cutting) I can hear the integrated fans in the laser that start to go faster. And even faster around 60%.
The job finishes, I extract the plexiglass and see that only the first 30% was clean cut all the way through, the other 30% had to be pushed to separate and the remaining 30% had almost 1mm of uncut depth so I had to throw them away..
After some minutes the fans return to the normal frequency and the machine has always operated perfectly since then. I have a fume extractor and an air assist pump.
Since then I started to give my machine a break in long vector cut jobs, thinking that's not what it was built for (just 30W), and maybe the overheating affects the laser power or maybe the machine lower the power for NOT overheating.
Is that normal?

[Gary Hair]

I can't say what is normal for that particular machine, but my machine, also a 30 watt, has run for several hours without any problems. I have one vector cutting job that I cut several thousand small holes in 1/4" acrylic and it takes just over 5 hours. I would call Epilog tech support and ask them what may be the problem.

Gary

[Scott Shepherd]

I agree with Gary, I have jobs that vector for 1 to 1 1/2 hours for each sheet, then I load another sheet, hit the start button. Never seen any difference in the first part to the last on a normal basis. I have had that happen, but it was because my lens got dirty during the cutting. But machine wise, we've not seen that issue.

[Dan Hintz]

Your tube is definitely overheating (though the increase in fan speed says the temp gauges are working as designed).

[Joe Kace]

I was told by Epilog that the fans going into high gear is normal. As time goes on, it kicks them up automatically to keep the laser tube cooler during longer jobs. My old Epilog didn't do this, but my new one I got in Sept 10 does. I also have no loss of power when this happens.

[Niklas Bjornestal]

Check so that the ventilation holes isnt blocked by something.

[Scott Weinstein]

Check your lens too. It could be getting dirty half way through your job which will hurt your power output...

[Giacomo Cheslaghi]

thanks everybody for your suggestions, next time I run a long cutting job, I'll follow your advices and let you know how the result will be.

Dan is there anything I can do to prevent the tube from overheating?

[Dan Hintz]

If it's overheating, something is wrong. As Niklas suggested, check the ventilation holes to make sure they're clear. It's a relatively new system, I assume (being a Zing), but if it wasn't I would suggest checking for an accumulation of dust on the tube's heatsink... this always cuts down on cooling capacity. I assume you are running this in an air-conditioned environment, not in a hot garage in Mexico?

The fans increasing in speed says the system recognizes the tube is getting warmer and is trying to cool it down (as designed), but they're obviously not able to handle the job. Epilog should help you with this one...

[Kim Vellore]

As every one suggested the problem points to the tube, but thinking outside the box, it could be your power supply heating up and supplying lower power, Maybe lower power heats up the tube.. I am not sure where the temp sensing is if on the tube or power supply or a combination of both. One more pointer to look into.
Kim

[Bill Cunningham]

If you have a 24" wide table, you may be getting a power drop the further your cut gets from the beam source. This could be normal, or an alignment issue.. Try cutting a piece using your normal settings at the furthest point of beam travel..

[Giacomo Cheslaghi]

Hi guys,
I took some time to do the cleaning plus I recently moved in a new location and it took longer than what I thought.
Going back to the laser issues, after I did the cleaning and I did some experiments on alignment issues moving the pieces to be cut away from the home position, I have seen:
1. after 5 minutes (or less) of cutting the laser loses power and can't cut through. The vents go on as normal and no I'm not operating the machine in a mexican garage (since I have air conditioning, it's winter and I live in Italy, same coloured flag but pizza instead of burritos)

and that would be bad enough but
2. recently the laser has started to leave dints (if that's the proper name) during the cut, which was smooth before. I made some pictures to explain, I hope they're clear enough..
I haven't changed the provider of the material which is a good one and not a cheap one...

any suggestion would be helpful, before I contact Epilog? (they have a great customer support, really!!)
187204187205187206

[Dan Hintz]

Starting to sound like your RF board may be on the way out...

[Rodne Gold]

Dann , dunno what tube he has , but with our coherents and synrads RF board failure normally results in a 1/2ing of power and then none at all when both fail.
Dunno what the dents you refer to are? Are they the small marks around the cut - they look like honeycomb flashback to me? The cut doesnt look good tho and I suspect that maybe an optic or a lens is overheating with time and either you losing power or alignment.

[Giacomo Cheslaghi]

For what concerns the tube, my Epilog has 4 months of life, and hasn't been used much since I'm starting up my business now..
Rodne you're right the small marks around the cut are honeycomb flashback... I have a cutting grid and I'm lifting the piece another quarter of inch but still I'm getting them.. I'll have to figure out how to get rid of them...
I'll write Epilog and see what I can do to check the alignment, they provide a plastic target to verify it, you mount it on the mirror and it shows with the red dot pointer if it's centered, and mine look fine..

how can overheating have something to do with alignment? I'm asking cause I'm new to the laser world...

[Rodne Gold]

Well,if a mirror overheats it can distort and the laser loses alignment and I have heard of lenses that have a hairline crack that reveals itself and interrupts the beam as it strikes the compromised lens and heats it more

[Giacomo Cheslaghi]

thanks for the infos Rodne!
when you talk about distortion of the mirror are you talking about a temporary status or a real deformation?
Cause when I engrave in raster mode (where the temperature is lower, I know) my laser works perfectly..

[Rodne Gold]

Temporary - when it cools it relaxes. The mirrors will have to be damaged or dirty to allow them to overheat tho.
To avoid the flashbacks don't cut on the honeycomb , put a piece of anodised aluminium on the bed/table (it absorbs laser) and elevate the perspex on blocks or pieces or perspex so its off the table.
If you can expose or open the tube chamber the tube on your machine , allow a very strong fan to blow on it after cleaning all the heat fins /fans of dust (with a dry paintbrush or canned dry air) , if it still loses power when being "supercooled" , then its most likely nothing to do with tube temperature