Problem with laser power

[waltfl]

Hi bob,
this sound to me that you have a temperature problem , if you cut with max power ( 18mA) then the temperature will rise 5 degree C and if you already on a start temperature of 68F then you be already on max temperature of 80F and this will lower the cutting power
because 3/8 acrylic is already a bit on the over thickness for a 40/45W laser usually is max 1/4 thick.
I would recommend to watch the thermometer, because I tell you if you don't watch the temperature you can be fast in overheating what can destroy your tube within minutes.
greetings
waltfl

Marco,

I ran the tube onto a 2 x 4 for about 25 minutes at 18mA. It charred a nice hole about 5/16" in diameter and about 3/16" deep. It was bright red the whole time. Nice purple straight line in the tube as well.

[bobkeyes]

Marco,

Here's my water setup. 5 gallons of distilled water in plastic container. Your pump, I just purchased, resting at the bottom. Tank is about 32" below the tube. Chiller coil resting in the water. Chiller is controlled by a digital temp controller hooked to a type "K" thermocouple. Controller set at 66 F. Water temp going in the tube and in tank is 66 F. Water exiting the tube is 68-70 F. Temps were measured with 2 different fluid thermometers. They were about a degree off from each other. Don't know how temp can be a problem, but I'll look at it again.

[bobkeyes]

I am in the process of realigning the tube and all of the mirrors. Since I'm not exactly sure what I'm doing it's taking a while.

[bobkeyes]

Sorry Walt. I thought that was Marco in the last post.

OK. Laser tube hitting mirror #1 dead center. Laser beam hitting mirror #2 dead center. Laser beam hitting head mirror dead center. Laser exiting tube dead center. Focus fine. Water temp fine, around 68-70 F on both ends.

Cutting 1/8" Romark sign plastic. I usually use 2mm and 100 power. Cuts in 1 pass. Now using 1mm and 100% it only cuts about 1/32" (that's a guess).

I don't understand. I needed 3 of these 3/8" disks. The first one cut fine at 2mm and 3 passes. The second one cut about 1/3 of the way around. It's been downhill from here.

If it was the PSU wouldn't the mA drop off? The PSU, the tube, and the alignment are the only things that I know of that could effect the cutting power.

Ideas....I need ideas!!

Thanks for all your help so far.

[bobkeyes]

Well Guys. It's bedtime on the right coast. Maybe you we can figure it out tomorrow.

[waltfl]

Hi bob
OK if you can only cut 1/8 plastic with 100% power and 2mm there is something wrong .
did you use the PPI setting?? don't do it because it mostly reduce the cutting power tremendous.
If you use 100% power and have set the DSP to 98% the mA meter should show over 25mA,
what is way to high and destroys the tube very fast probably in a couple hours.
does the tube anode rings look like red hot?
I have around 1840 hours on my tube ( 40W) and I cut 1/8 acrylic and wood with 48% power and
5 to 6 mm/s.
what kind of lens you got?? did you set the distance between the lens ( laser head ) and the surface of the material
right?
make slope test put a strip of material across and lift one end about 1/2 inch higher then cut a line
with 45% power and 5mm/s speed , then look where the line is the thinnest, measure the distance
from the surface to the laser head , that's your focal length what you need for your lens.
I hope this helps
greetings
waltfl

Sorry Walt. I thought that was Marco in the last post.

OK. Laser tube hitting mirror #1 dead center. Laser beam hitting mirror #2 dead center. Laser beam hitting head mirror dead center. Laser exiting tube dead center. Focus fine. Water temp fine, around 68-70 F on both ends.

Cutting 1/8" Romark sign plastic. I usually use 2mm and 100 power. Cuts in 1 pass. Now using 1mm and 100% it only cuts about 1/32" (that's a guess).

I don't understand. I needed 3 of these 3/8" disks. The first one cut fine at 2mm and 3 passes. The second one cut about 1/3 of the way around. It's been downhill from here.

If it was the PSU wouldn't the mA drop off? The PSU, the tube, and the alignment are the only things that I know of that could effect the cutting power.

Ideas....I need ideas!!

Thanks for all your help so far.

[bobkeyes]

My Power set up.
Max power set in Lasercut is 62%. That means that max mA is 18-19. That's what I use. When I say I ran at 100% it is using these setting.

Nothing has glowed red that I know about. My laser tube is hidden when in operation. When I did the 2 x 4 test burn I climbed behind the machine and watched it. Saw nothing unusual.

I have run the focus test twice now. It is at about 52mm. Lens came from LO about 6 months ago. It is clean.

This laser is a part of my business. I am about to get into a crunch here. I have jobs promised and my time is running short.

I appreciate any help I can get. Thank you.

[bobkeyes]

One other observation. When the machine starts it's cut it seems to be a full power for about 1/8". Then it drops off and seems to get less and less the longer it runs.

Bob Keyes

[bobkeyes]

OK. It's about time for you folks on the left coast to get up.

Any thoughts?
Bob keyes

[Tech_Marco]

I think there is 'voltage leaking' somewhere if the tube is running fine. When you did the 15 min test, did you test the fire power right before turning it off (at 15min). Was it still able to burn good? What I mean is that whether the laser output stable or not from min 1 to min 15? I know that you got a nice burn hole but you don't know when did happen. Could be the 1st min and nothing after the 2nd min or it burn well continuoulsy. Light up on the laser tube (internal) doesn't mean there is output.

So, I need you do do one more time. Power up the tube and test the firing power right before turning it off by move the wood block 1" away. That way, you can tell if the beam is full or "power" and be able to cut.

If it is good, that means something wrong with the power supply or the cable


Marco

[bobkeyes]

3 burns at 18 mA. 15 min each.

I don't see it being the power supply because it never wavers on the 18 mA it's supplying. Anyway here's the pic.

Pulled out HV cable. I see NO problem there.

[Tech_Marco]

So, there is no problem on the laser tube and the laser power supply. I'm curious how come power get less and less when doing cutting job. When the problem happen (less power), was it doing on the same spot or in different location? Did it make difference when doing cutting closer to the corner (home) and further away from the home? Try doing cutting in different location.

Marco

[Tech_Marco]

By the way, are you using the same wire to connect the power supply to the negative side of the laser tube? Or, did you use other cable instead?
Double check the negative cable may be it is bad.

If not, do more cutting on the location where you could get a good cut of the 1st pass. Then, do the second cut, 3rd cut... on the same spot. see if problem occurred.

Marco

[waltfl]

hi bob
the only point where the cutting power looses power over time is the water temperature.
put your temperature sensor about 3 inches away from the tube inlet directly on the water tube and watch
the temperature.
if you have not additional cooling power like peltier or chiller or like me with a A/C unit and radiator the water cooling will not be enough.
during cutting with 18mA the water temperature will rise about 8 degree F within 3 to 5 minute and with every degree rise the cutting power goes down about 10% .
believe me I have learned my lesson and paid for 3 tubes befor I got this now my tube has 1,640hours on it and I still can cut 1/8 with 5mm and 48% and 1/4 with 3mm/s with 51% power,
here is a picture from my window A/C setup
greetings
waltfl


quote="bobkeyes"]3 burns at 18 mA. 15 min each.

I don't see it being the power supply because it never wavers on the 18 mA it's supplying. Anyway here's the pic.

Pulled out HV cable. I see NO problem there.[/quote]

[bobkeyes]

waltfl,

I understand, but I have a chiller running at 66 F. After long cutting, 3 hrs. continuous, session the temp only rose about 2 degrees F. Checked exit water temp yesterday with fluid filled thermometers. Exit temp of water is about 68-69 Degrees F. Tube is filled with water and it has GOOD flow.