Tube advice - new tube dead(ish) after a week?

[Graham Facer]

Hi Guys,

OK in my quest to get a decent laser cutter, I decided I had to try a new tube so I took the plunge and got a EFR F6 from an ebay seller. The tube packing was excellent (crate/tight foam/box/tight foam/box/laser with diecut foam) and the tube seemed and still seems perfectly intact. I hooked it up and once I sealed the wiring - it was cutting nicely and the beam looked perfect. So then I aligned it and left it for a few days (max Thursday -Monday). On Tuesday, I turned it on and got beam in (some of) the attached pictures. So basically beam on the ends and very little to no beam visible in the middle. The beam also dips down at the end to the metal as is clear in the photos. Some does leave the tube but not much.

Wanting to rule things out, changed the power supply to a unit from our other working machine and got the remaining pictures (date stamp is in name).

Altering the power level does little. The cutting may be off as I jiggled things in between but when I hit the laser button, I do get action at the table, but a test program basically does not cut.
Last week I basically did not cut - I just set up, aligned, test cut, and checked power levels (analog ma gauge) and never showed above about 24-25ma and even that was only to see how power level effected cutting but it was cutting worse so I dialed it back down. I am using a reci 150w power supply for my original z8 tube with this F6 (replacement was the same).

So I don't think I cooked it as I was careful to increase power slowly. For now I am just focused on the tube. Cutting may be affected by alignment currently - but I know what the beam should look like and its nowhere near that.

Other relevant facts:

I once got a shock (laser off - presumably from power in capacitors) near HV end of tube after this started. No arc's from that connection when running last week or this week (though I did have arc's at the splices that I had to deal with). My finger was basically at the edge of the white on the back end of the tube (epoxy I assume?).

On the first start this week, I forgot that it was warm and did not let the water chiller cool down much so I got an alarm. But the water was flowing - it was about 25c water. I shut off immediately after about 8 seconds maybe.

Tube was stamped May 27th 2015 (and I received about June 3) - so its brand spanking new - but it leads me to wonder if a CO2 leak could have been occurring and just not finished yet. The beam does seem weaker today than Tuesday but I can't be certain all the levels are the same with a new power supply.

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[John Noell]

Sure sounds like a bad tube. However, are you positive your grounded ("earthed") end has a solid connection?

When you look at the mirror end, do you see any sign of a crack? I had a RECI crack almost immediately on install. (They did replace it, but VERY reluctantly).

[Graham Facer]

Not sure which mirror end you mean. The front looks fine (clear and perfect really) and the back is opaque. Both look fine but there are some epoxy runs across the back of the HV side end mirror that sort of look like cracks in the photo.

IMG_20150611_113824.jpg IMG_20150611_113904.jpg

As for the return connections, the tube came with wires on and those little rubber sheaths, which I then taped too but they don't really slide so I can look at the underlying soldered connection (or however it is under the sheath) - same on the HV side.

[Graham Facer]

Also a link to video if this works...

https://goo.gl/photos/P1FjQJcYaxoNbEAq9

[Dave Sheldrake]

A few things brother

The F6 is a 130 watt Tube not a 150, the 150 is 1850mm long and won't fit in the std 1200 x 900 machine without an extension. The peak power of your tube is 150 but unless you are providing enough current the most it will make is about 140 when new dropping to 135 watts or so when it stabilises.

Sheath that HT wire!!

Get some 2mm - 3mm wall thickness silicon tube with a 6 to 8mm bore and fit it over the entire length of the HT side from the white connector at the PSU up to the point it joins the tube, having it taped to the tube isn't a good idea either,(without getting boring it's to do with plasma stability being affected by the field around the wire etc etc) so sheath it and try test cuts again

You should be seeing about 29.5 - 30mA when the tube is running at full power

cheers

dave

[Graham Facer]

A few things brother

The F6 is a 130 watt Tube not a 150, the 150 is 1850mm long and won't fit in the std 1200 x 900 machine without an extension. The peak power of your tube is 150 but unless you are providing enough current the most it will make is about 140 when new dropping to 135 watts or so when it stabilises.

Hi Dave,

Yes I had an extension when I was using the reci V8 tube (sorry said z8 before) so this one fits better but I have to cover up the hole eventually. The top cover doesn't shut anyhow as the mounts/mirror/everything are too high.

Sheath that HT wire!!

Get some 2mm - 3mm wall thickness silicon tube with a 6 to 8mm bore and fit it over the entire length of the HT side from the white connector at the PSU up to the point it joins the tube, having it taped to the tube isn't a good idea either,(without getting boring it's to do with plasma stability being affected by the field around the wire etc etc) so sheath it and try test cuts again

You should be seeing about 29.5 - 30mA when the tube is running at full power

cheers

dave

The wire has never been sheathed (other than the internal silicon sheathing under the red sheathing) and I will need to splice it as the new tube only had stubs- I also spliced at the power supply as my brother had cut off the ceramic connector.

Getting the sheathing should be fine as I am down the street from 2 large electrical supply houses but there is a splice about 24" away from the HV connection on the tube as the new tube only had a tail. Also another splice instead of the ceramic connector - my brother I guess had arcs from his so he cut it off and spliced it.

So any suggestions on a reasonable practical way to seal that splices? I assumed if the arc'ing was gone it was OK, though I did notice some charge on the tube (static feeling) so certainly willing to have another go at this.

The vendor had it taped to the tube - I thought for stress relief on the joint but I can undo that.

As far as 30ma - I'd be fine with the 24ma I had its just that right now I've got basically 2-3ma.

I'll look at the connections and take pics of the factory connections. Not sure how I would seal them better - not really happy with just the sleeves they had.

[Graham Facer]

So this is how the factory/vendor had the HV wire and low voltage wire connected. Both need splicing to the old lines and then another splice for each near the power supply (HV to bypass the now removed ceramic connection and return to go to ma gauge).

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I guess the main question is - do you think this is a connection issue even though it had worked fine day before with the same connections (as sealed not as shown here without splicing tape).

[Dave Sheldrake]

Silicon tube is your best friend

Get some big diameter stuff and cover the joints although to be honest for the few bucks they cost I'd give Ray a call at Rabbit and ask him about a new HT line (they don't cost much and are the root of all evils)

Sticking the wire to the tube is a big nono in any DC laser system, there are a whole host of problems it can cause, one of the biggest is leakage, the wire can lose current when in contact with any of the machines metal parts and the Rf field it generates will destabilise the plasma arc. Given that the EFR F series are VERY reliable I'd suggest you are losing that 20+ mA into the machine chassis from either the joints or bare HT line.

[Dave Sheldrake]

Rotate the tube to get both end inlets and outlets at about 45 degrees above horizontal, as it is you run the risk of bubbles in the mirror chamber (cracking the full reflector mirror/ dead tube time)

The factory connections are usually very good, they use a small push on clip that holds to the tungsten electrode very nicely.

Looking at that wiring I'd suggest 99% of your problem is current leaks

[Dave Sheldrake]

graham.jpg

You will end up with a trapped bubble here, that will kill the tube in under a minute

[Graham Facer]

Well I'll try the silicon first but is it not odd that I'd leak current on a Tuesday but not the prior week? Seems like a lot of leakage without an arc?

If I get a new line, I'll still have to splice to the tube wire (as I don't plan on giving it a go soldering if I can help it).

But yes I do like the EFR F6 and I bought it because you spoke highly of them - nice beam profile when I had it (though on lower power it seemed to have an outer ring to the marks that went away when I increased the power).

[Graham Facer]

graham.jpg



You will end up with a trapped bubble here, that will kill the tube in under a minute

So take it out of the mounts and raise it 45deg up front and then back? or rotate in the mounts (which I have done)?

[Dave Sheldrake]

Rotate Graham, make sure that any bubble that forms has a way to move upwards without getting trapped

Well I'll try the silicon first but is it not odd that I'd leak current on a Tuesday but not the prior week?

HT wire breakdown tends to be gradual and incremental, if the line fails it weakens the insulation so leading to more leakage over time.

But yes I do like the EFR F6 and I bought it because you spoke highly of them

A bit of tinkering and you will see the benefits when it's running at the sweet spot the profile really is unmatched by anything under a GSI

[Graham Facer]

Well I'm encouraged we the consensus so far isn't that the tube toast...

Until tomorrow when the stores open.

Oh and no bubble visible in any way shape or form and rotated both ways (though I was sure already never hurts to check).

[Dave Sheldrake]

Oh and no bubble visible in any way shape or form and rotated both ways (though I was sure already never hurts to check).

Keep in mind that bubbles can be formed by cavitation even in a closed system. I leave all my chillers on 24 / 7 to avoid the bubble issue as far as possible.