Chinese laser axis movement problem... Any thoughts??

[Shane Kretsinger]

So... I have a 2 month old 50w Chinese Laser and have been doing the usual "getting to know you" projects and figuring out the way it works.
The machine seems to do a decent job and I dont have expectations that it will know how to sing AND dance... I just need it to sing.

Yesterday I hooked up the rotary engraver for the first time and did some engraving on a painted stainless steel cup.
The engraving was working fine and about 80% of the way thru project I heard a "snap" sound from the machine... Almost like the sound of an electrical arc or a breaker tripping.
Then the laser continued firing but the print head stopped moving.
The program kept progressing but the laser just kept hitting the same spot.
I tried to move the carriage with the bump keys and it would not move.
So after determining that the machine was not going to recover I paused the print and hit reset and then restarted the machine.
This cleared the problem but the project was ruined since I could not start where it left off due to the program progressing while the print head would not move.
Also restarting the machine moves the axis to zero and a restart simply wont hit the same points.
So...Project ruined...oh well.
As I said... rebooting the machine put everything right again.
SO I ran another job on the ruined cup to see if the problem repeated... The same issue happened at an earlier stage in the print this time so I dont think its an issue with the print file.
Then I loaded another engraving file and tried it again... Same problem after a few minutes of engraving.
So, Thinking that it might be an issue with the rotary device since this never happened before, I removed the rotary device and tried engraving a flat job since I had never had an issue like this before on flat jobs.
The same thing happened again after about a minute of print time this time on a flat job... So this seems to eliminate the problem being caused by the Y axis stepper motor or the rotary jig stepper motor.
I thought ( I may have fantasized) that I saw a flash of white light from in the vicinity of the Y axis limit switch so I put a metal object in front of it and it turns red and then goes out again when I remove the screw driver.
So... I have no idea what is causing the fail... I ordered new limit switches since I have seen on YouTube that they do fail eventually but haven't seen any failures described to be like mine. (The switches were 4 bucks each so why not have them on hand)
So... X axis problem? stepper driver problem?? limit switch issue?
If anyone has any ideas I would be thrilled. Otherwise, after I sort this out I will post what I determined the cause to be when I figure it out.
In the mean time the laser is not reliable and I will obviously not run projects that cost money when they get fouled up.

-=Shanek

[Doug Fisher]

A wire in the harness of wires going to the moving head that is no longer connected well or broken within the harness and this intermittently losing connection? Stepper controller going bad?

[Rich Harman]

Did both axes stop responding or only one? If both, do the axes each have their own separate driver or are they driven from one board?

Hearing an audible arc coincident with the axes ceasing to move makes me think that you should check your laser tube and make sure there is no arcing happening. The arcing could be causing the control board to glitch.

[Joseph Shawa]

An arc anywhere within the case might reflect and be seen from the top. My older supply cord wasn't an exact fit with my new one and it arced. I also had a situation where my x axis controller wire became grounded to the case because it had been misrouted an was chaffing on the leveling pad screws. Also, make sure the machine is grounded WELL.

[Shane Kretsinger]

Both Axis stopped.. it just sat in one lace and kept firing the laser and the program window on the control board showed progress... but no movement of laser head.
Good idea... I will try running it again and maybe put my gopro on the laser tube connections... That way I cant miss it if it arcs...

[Shane Kretsinger]

I have a ground rod with good connection and I did double check that... I was thinking static buildup too... That appears to be in order.
I will check the controller wires for pinches. Thats a good idea too. I think I will run my gopro video camera and see if I can isolate the arc... if that is actually happening. SO hard to be looking in the right place when the blip only happens after several minutes. Thanks for the suggestion

[Shane Kretsinger]

Two control boards... good suggestions both... I think I will set up a video camera and try to capture the real/imagined flash that I think I saw. That will likely help isolate the issue too.

[Shane Kretsinger]

OK.... So here is the deal... If it looks like a duck, walks like a duck, and talks like a duck... It might just be a duck.
Found that where I had spliced the high voltage lines between power supply and tube and then wrapped them in electrical tape there was an arc.
The high voltage was going right through the tape due to inductance I suspect.
I wrapped the connections in duct seal and then taped them up again and problem solved.
So... lesson? Very high voltage laughs at electrical tape for insulation... do better.
Thanks for all the suggestions, problem solution turned out to be about 5 cents worth of repair.
Hope this helps someone else too.

[Matt McCoy]

It might be a good idea to slide silicone tubing filled with RTV over the splice.

[Bill George]

You have to remember we a looking at 20,000 volts more or less. Electrical tape is not going to do it. For a couple bucks you can go to a good auto parts store and purchase.... what 2 feet or whatever of HV spark plug wire with copper core, for less than $5.

[Rich Harman]

You have to remember we a looking at 20,000 volts more or less. Electrical tape is not going to do it. For a couple bucks you can go to a good auto parts store and purchase.... what 2 feet or whatever of HV spark plug wire with copper core, for less than $5.

How does that solve the problem of where the splice needs to be made?

I had to make a splice in the HV line. I used electrical tape. Then I used more electrical tape, and some more and then more etc., until the insulation was about 1/4" thick. So far it has worked well.

[Bill George]

Simple, no splice needed. One long wire.

[Rich Harman]

Simple, no splice needed. One long wire.

Not so simple on my power supply. The power supply end of the HV line was terminated in a non user-serviceable way. I don't actually remember how, but it was not something that I could replace - and I do electronic stuff all the time.

[Rich Harman]

I had to make a splice in the HV line. I used electrical tape. Then I used more electrical tape, and some more and then more etc., until the insulation was about 1/4" thick. So far it has worked well.

Funny that not long after writing about my electrical tape splice my HV line started shorting. At the start of each cut I was hearing a "snap" from inside the cabinet. My first thought was that I was going to have to admit that maybe electrical tape isn't up to the task after all. I hate having to admit mistakes. Well maybe "hate" isn't the right word, it is humbling to do so, so I don't mind all that much.

Anyway, I am not faced with that just yet. The arcing was occurring further up the line where it was resting against the metal. It had developed a pinhole in the insulation. I'm thinking that the HV line is not quite high quality, and originally intended for an 80W tube and power supply. The higher voltage of my new power supply must be too much for it. I'll look into getting some better wire - is spark plug wire a good alternative?

For now I put four wraps of electrical tape extending a couple inches past the pinhole - which makes 8 layers of tape. Then I wrapped the entire length of wire (what was accessible), so that makes two more layers of tape, or ten layers over the pinhole.

Here's a couple pics;

IMG_2494.JPG

IMG_2498.JPG

[Matt McCoy]

Outside of replacing, which is what I think I would do, you could shield the length of the HV with silicone tubing and RTV.