Has anyone seen this before, or has any idea why it’s happening?
I noticed some of my cuts were not cutting through the 3mm MDF at certain points. For example I cut a circle it always cuts fine for 3/4 of the circle but the last 1/4 is a little less powerful.
So as a test I upped the power (from 40) to 80 and the effect was exaggerated to the point where only the 1st 1/3 of the circle cut though and the remaining amount didn’t cut through at all. It’s as if the power gradually lowered to the point of no output.
I’ve attached an example - Left is 40 power, the middle is 80 power and the right is 20 power.
Although you can’t tell from the photo neither of these 3 have totally uniform cuts. But the 80 power one really tells the whole story.
Any help or advice would be appreciated.
Edit - Another strange observation…If I fire the laser at say 10 output and look at the tube I can see its firing, and its faint as you’d expect. If I fire it again at 80 (again making a circle) the tube is firing consistently and brightly - even though the laser isn’t making it to the lens.
Test the beam for the proper resonance mode, known as TEM00. A previous discussion goes over the details (start here and read the next few posts):
If the tube isn’t operating correctly, it won’t focus correctly, the energy density drops, and it no longer cuts well. It seems tubes can vary between between “working OK” and “yuch” without anything else changing, although now as a gradual change during a single cut.
However, a high-power diode laser may be fading out due to overheating. The heatsink / fan may be, shall we say, underspecified for the job or the cooling channels may be clogged with condensed fumes / soot / dust / crud.
In any event, that situation should become a separate thread, rather than confusing this one.
Have you done the TEM00 test to check the beam shape? If not, now is a good time.
It’s not clear what you mean, though. The gas discharge through the tube axis (which is what makes the laser a laser) tends to narrow and bend where it meets the cathode electrode inside the tube. Some fluttering seems normal, but anything more exciting is probably a Bad Sign™.
I did another test though - i have a new/unused Ammeter. I wired it up and it showed zero loss of power.
When cutting a circle at 80% power it read 35-40ma for the whole duration of the cut. But sadly the tube seemingly stopped cutting (or marking the MDF) by around 1/3 of the job.
I did other cuts at various powers (15/20/30/40/60) and the Ammeter showed constant power on all of them.
Do you think the assumption then is the tube is the problem and not the PSU?
Those spots don’t look obviously bad, which rules out a permanent problem.
Unless the machine has a very high power tube, that level of current is high enough to damage the tube, particularly if that’s the normal setting.
What is the tube’s power rating?
Given a constant current from the power supply, what’s left is the tube failing to lase, which means it’s time for a new tube.
Opinions differ, but IMO power supplies are relatively cheap, so I’d replace both at the same time.
Now that you have a way to measure the tube current, I’d adjust the power supply’s trimpot so it delivers no more than the tube’s maximum current, whatever that may be, and recalibrate all the cut settings (power & speed as needed) to match the new hotness.
I’m working my way through the advice already given (by @ednisley et al), but it looks more like a tube problem than a PSU problem to me (with respect). How old is the tube? Are the tube and the PSU appropriately rated for each other? How long is your tube and what wattage is your PSU supposed to be for?
its an 80w tube, but I never actually ruin it at 80power, its usually run at 20-30. I’ve only been using it at this power for these tests, and only for very short times,
thanks for the help - I think to save myself the agro. I’ll do as you surgest and upgrade both!
ahh, that’s the unknown. The tube is rated as 80w, but I have no idea what the PSU is rated for. Its Chinese and I dont think there’s any marking on it at all.
Its had a good 3 years worth of use, so might be time for a upgrade!
Upgrade? Replace like for like IMO… What is the tube? Length, diameter, make? People often DO replace PSU and tube at the same time, but I’ve found it not really to be necessary.
When PSUs go they usually either go completely or lose half their power as one or other of the transformers fails (depending on its quality). Would love to see some photos of both, as I’ve seen a great many PSUs and tubes in my time.
PSUs are relatively cheap as @ednisley says and replacing it first will at least work as a diagnostic, if you’ve a spare $200USD to mess around with!
80 power = percentage of power supply’s maximum output current (roughly proportional to tube power output)
If 80% of the maximum power is 35 to 40 mA, then the power supply will deliver about 50 mA at 100%. That is grossly too much for an 80 W tube.
When you run it at 20% to 30%, the power supply produces a current between 10 and 15 mA. @jkwilborn has a table of tube sizes & currents suggesting that’s over half the normal current for an 80 W tube, so any power settings higher than than 50% would constitute tube abuse.
The rule of thumb is to set 50% for a manual pulse, then adjust the power supply’s internal trimpot to deliver half the tube’s maximum current rating. Then 100% (or 99%, whatever) cannot drive the tube over its maximum current, but you must adjust all your speed & power cut settings for the new reality.
bonjour, je pense que c’est peut être un problème d’alignement des miroirs, le 40 et 20 me paraisse corrects , par contre vous devez avoir du jeu quelque part car la fin de découpe ne correspond pas au début…
Pour Le 80, on dirait qu’il n’a pas aimé la puissance maxi…
Moin. Ich bin nicht sicher, ob es auch für eure Laser zutrifft und ich weiß auch nicht, ob es schon jemand geschrieben hat (ich habe nichts darüber hier gefunden) Der Laserstrahl ist nicht rund sondern Rechteckig. Kann das die Ursache sein. Ein Rechteck wandert im Kreis.
