Hi , don’t if anyone has had this before or could point me in the right direction.
The issue is this , I have a k40 and I replaced the tube about a year ago and everything was fine , I was cutting 3mm ply at 30% with 2 passes
Now it cuts in one pass but burns the edges, i can set power anywhere between 10% and 80% and it still the same, if i go below 10% it does not fire the laser .
Any know why this would happen or how I can test to find the fault
thanks
30% set how, digital front panel or some other way?
Also, do you have an analog Ampere meter on it and keeping it below the rating listed on the new tube?
I have both digital and analog
The readings are the same as before the issue
30% on digital front panel and about 12 on the analog amp meter
If you don’t know there’s an FAQ to the top-right of this page with lots of information about K40 laser cutter/engravers. I can’t stress enough reading through it even on things you think you don’t need to read about.
The reason asking about the display is explained in the FAQ. Most people with K40s without the analog meter or without understanding what overdriving the tube does will burn out their laser tube in a year or so. If you don’t run your tube over 12mA( I hope that’s what “12” meant ) then you likely didn’t over power it and wear it out. But another way to test is to look at the TEM patturn coming out of the tube before the 1st mirror.
You want TEM 00
You didn’t mention anything about what you’re doing or skills so I have to mention things like checking your focus, checking mirror alignment and cleaning, lens cleaning and what about air assist, is it still functioning and at the same velocity as it used to be at?
And those digital displays are all but worthless unless you have done the work to map out the display numbers with the current applied. I’ve seen people mention they never went over 40% but when they measured what that was it was 24mA and way over the max tube rating.
Thank for the useful info , I use the cutter for making wooden puzzles
I have check all the alignment and focus on the mirrors and all are fine
I have air assist and that’s fine
I have checked the tem and it’s a single dot , tem00
Nothing has changed on the setup since last use 6 months ago which is why I am confused as to why it has started burning on any setting
Something HAS changed and that is why we’re checking things, ie to find out what has changed. You wouldn’t believe how many times people have spent hours helping people out with things which “nothing changed” only to then hear things like ‘oh ya, I didn’t think that was important’.
Things which do change over time can be the cooling water, the coatings on the optics, the gases in the tube the capacitance/operation of the LPS. Just to name a few.
What control board do you have? M2 Nano?
What software are you using?
Sounds like it’s just running at 100% power. Could be something wrong with the digital panel or the control board. My k40 doesn’t have the digital panel anymore so I’m struggling to remember the setup. Maybe @donkjr has some thoughts.
Yes it’s M2 nano and I’m using whisperer
OP said only 12mA of current though and I would expect 100% to be up around 24mA with a new tube. But does seem like some kind of control issue with it blasting through in 1 pass vs 3 passes if the speed hasn’t changed. The OP could put a volt meter on the output of the front panel and see if the voltage( to LPS-IN ) is changing with the power changes on the control panel.
Jack was right, it’s LPS-IN which is the center of the POT/front panel voltage divider. The LPS-IN voltage should go from 0V(0%) to 5V(100%) if I remember correctly.
Image from Don’s K40 pages:
Front panel control on these is simply a pot across 5V and ground and fed to the IN input on the laser power supplies (lps) I work with. If L is the same as IN then you can do this to test it, but it’s likely if it works at all, this is OK.
Where did you check the resonance mode? Some tubes will resonate in TEM01 mode if not driven hard enough. It’s very hard to determine if it’s an lps issue or the tube is failing. A new lps is likely the cause, as the current is very low, and is lower cost than a new tube.
It could be either. There is no reasonable way to test the combination of lps and tube other than check the lps inputs.
I have a 50W machine, not a K40, so @dougl is likely your best reference.
Good luck.
Thanks for the feedback , I have not had a chance to try testing yet , will give it a go at weekend and see how it goes
Ignore digital, go with the analog current measurement! Stay under 18ma is my recommendation. My K40 is 6 years old and still running the original tube because I am religious about keeping the current in hand.
If you are burning the edges, air assist flow, spread beam (focus issues), dirty optics and alignment come to mind.
Fully agree with ignoring digital but if they don’t have a POT for adjusting power and the software only controls on/off then he’d need a way to adjust the power.
Also, the 18mA limit is only for the stock tubs which were really 30-35W tubes so a new tube, if good quality, can be run at full power(listed on the tube) to get a full 40W of output and it will not degrade the tube. They test at 45-50W and sell it as a 40W for that reason.
I had to read his post a 2nd time to notice he is seeing it cut in one pass what used to cut in 3 passes so something is changing the output power or locking it at full power.
This might sound really dumb, but aside from the many excellent ideas and suggestions you’ve already had.
Have you started using a new or different batch of 3mm ply? I’ve had variances like yours, at times, and I kind of came to the conclusion that it is the different ply. Maybe they have more glue or something, maybe a different glue, that causes the problem. I can leave all my settings the same and still get a variance, like you have, just by using a different sheet of ply.
Just a thought.
Ok so here is where I am upto
Tested LPS IN it does change when front panel is changed , 0v to 6v from 0 to 100%
Lens and mirrors all clean and focused/ aligned correctly
Air assist is working fine
Tried 4mm mdf and that cuts in 2 passes but also burns on edges
Could this be a software issue , I may try removing and reinstalling anyway just to be sure
I’m curious where you are setting the focal point to?
Also wondering how the machine used to cut your 4mm MDF which I’d thought was not a good idea without taking great care to remove the toxis fumes.
And if you want less charring then lower the power and increase the speed and air assist.
And does the laser power output change with the change in voltage at LPS-IN?
Just need to keep in mind how these work. All of these seems to show RMS values, normal for an analog meter, but a digital meter must sample the input, it’s the sample time you have little knowledge about.
The K40 turns the tube on/off as @dougl states, unlike my co2 which sets the current limit at the laser power supply (lps).
I’ve used this chart for a while and find it pretty accurate.
Measure the tubes length to get a better idea of it’s current limit. I’ve seen K40s from 720mm down to about 650mm in length.
My last tube came from Light Object and is rated for 50W and is 1000mm in length. It will produce 50W at 13mA and 65W at maximum, I think is 24mA. My lps is set to maximum current draw at 100% power in Lightburn. I run it at 100% when needed and don’t worry about the tube. It’s a 50W tube.
I have to disagree for things like the K40 which has a shorter tube, more like 30W. They sell these as 40W machines and they aren’t.
Most of these seem to put in a 40W tube and say it’s 45 or 50W, not the other way around. A good replacement tube with documentation will advise you of the current and watts out.
@dougl what length is your tube?
@dougl made me think about your lens. Did you take it out and clean it recently? Do you have it in the correct orientation?
Ya, I was talking about the fact that the OP has a replacement tube so it’s no longer the cheap stock tube. For all we know the OP has the classic tube cover extension on his machine because the replacement 40W tube is too long to fit in the stock box.
