My K40 stop cutting

I have 2x K40s, from different vendors, so they are a bit different (both digitals)

Both have the same time (1 month), and the same working hours. Both have been using always at 30% power, and both at the same time.

But one of them has stopped cutting, as it has a very low power. Have tried to cut at 30%, 50% and even 80% power (just a tiny 10mm x 10mm box), and I always get the “same” depth: just like engraving.

What should I check?

Also, I have ordered 2x MiniGerbil, that will be here this monday I guess. Should I install it before making further tests?

PS: due to strange circunstances, I can not contact or get help from vendor: he sent me it by error and I ended paying just 100€ for it.

I am checking my machines and the “broken” one is smaller: instead a 72mm laser, it has a 63mm one. It says nothing about power, but looking at description in his eb, some places says “30-35 w” in others says “40w”.

Notice that both machines where cutting at 30% power, and at the same cutting speed.

Do you mean power or temperature?
Post pictures of the control panel, LPS and controller on the failing one.

Post a picture of a test dot taken burned at the correct focal point on the surface.

Sorry, I mean power (edited).

what test dot can I download to “print”?

Just put something (card board, paper, tape) under the head and do a test fire.

Do you hear any crackling, hissing or arching when you hold the test fire button with the laser enabled?

What kind of coolant are you using?

Ok, I will do it tonite. Any way there is not anything unusual. No strange noises… I will look for archs. Just the deep of the burn is not deep enough to cut.

Since you do not have a ma meter it’s hard to tell how much current the tube is drawing.

Usually this kind of symptom is the result of bad alignment or power supply.

If you have not done an alignment lately I would do that first.

Yes, I did align, and it is fine.

Anyway, I have bought a multimeter… where should I measure? (notice I am very afraid from electricity since 3 y.o.!)

Please show me a picture of your meters face.

The same as the other thread :slight_smile:

Notice we are talking about 2 different machines. This one is the “broken” one. The one in the other thread is working “fine”

This the LPU from the “broken” one:

ps: what is the “test” button for?

The test button down on the LPS fires the laser independent of the state of the other control signals on the LPS interface.

Run the same Laser current vs % power as you did on the working one…

Here is the values of machine B (the one not cutting)

10% 5.4
20% 9.6
25% 11.40
30% 13.11
35% 14.42
40% 15.7

Just to resume:

Machine A: a 40w one, 700mm laser tube.
Machibe B: a 30w one, 600mm laser tube.

I always thought they were the same ones (a 40w), so I used both always at 30% power (cutting speed 6 mm/sec to cut 3mm MDF), and both were able to cut. So, A has been running at 7.3 mA and B at 13.11 mA.

Now, B has stopped cutting: I am now testing at 22% (aroud 10 mA) and needs around 4-5x pases to cut at 5 mm/sec speed.

Is the B tube “burn”?

I was checking tube prices and a 600mm one cost almost the same as a 700mm one. Of course, the 700 does not fit inside the box… can I make a hole in the box to fit it? Will it work?

you would be surprised what size tubes people have put into K40 laser cutters! Scroll down to look at the pictures of this upgrade: Laser Cutter Upgrade... upgrading the K40 (Micromark version) - Modeling tools and Workshop Equipment - Model Ship World™


I had a problem with laser not giving much power after only 1hr of burn time on a new K40.

Tape on the first mirror showed no dots at some power levels and multiple dots at others. Tube was fried - and received a new one under warranty.