View Full Version : Cracked lens stops work...

Ian Stewart-Koster
08-02-2017, 1:14 AM
Last night, lasering with the big machine went well.
Started a huge job today, and it scarcely melted the acrylic, but smoke was coming out of the top of the tube and around the mirror on the head.
Oh no!
This is a pic of the lens. 4" focus.
It's not much of a mark, but it has rendered the machine temporarily useless.
I do have a spare 20mm lens on hand, but it's only a 2" focal length lens, and won't suffuce in this unless I hacksaw the nozzle shorter- major panic at the moment...
(and the little M300 is playing up- Y axis issues again. Might have to resort to CNC routing all the acrylic again... yuk.)

I'm surprised such a little mark made such a huge impression on the lack of beam, and heated the tube up so much-there must be a lot of back reflection or something.type

P.S. the liquid in the bottom of the tube, in the photo, is IPA that I used to clean it- it just hadn't all evaporated yet when I took the photo

Ian Stewart-Koster
08-02-2017, 3:09 AM
A question for those who've done it before...!
I had a 2" focal length lens @ 20mm diam that I bought 6 months ago 'just in case', but this broken one was a 4" FL lens.
So I put the 2" lens in, and set up a ramp of acrylic to try & figure the sweet spot for focus, without the air assist nozzle.

I got a beam that was nice and fine in places, but it WON'T cut the acrylic at power & speed settings that used to work fine before.
Here's a photo of the test ramp.
What also surprises me is I never noticed the lighting up or illumination inside the tube before.
Is this normal, or is it indicative of worse things to come? (eg the mirror in the head dying or something) or a function of the cheap spare lens I got from China?

The tube got quite warm too, just doing this test cut- when no air assist was present to help with cooling I guess. (Too warm for my comfort)
I was also surprised at the glow you can see reflected off the acrylic in under the lens - with the tiny air assist nozzle, I never noticed such before - I'd have sworn it was nonexistent, actually.

Thanks for your time!

Mike Lysov
08-02-2017, 3:09 AM
Hi Ian,

It is no surprise it's cracked. If there was any dirt sitting on it it would start building up, made the lens heated and cracked.

Where are you in Brisbane? I have 4" lens(at least it is claimed to be 4") 25m in diameter and about 2-3mm thick.
However it is not a tube lens, it is the one used in my laser head. I have bought it for US$110 to increase depth of field. My laser uses 3" lens.

I can lend it to you for a few days if you promise to return it in the same excellent condition. I am located in Kenmore Hills.

Ian Stewart-Koster
08-02-2017, 5:30 AM
Hi Mike - we lived in Kenmore back in the 70s! Thanks very much for the offer - I might take a rain check for the moment though. This Golden and also the Universal take 20mm lenses, not 25mm. We're not in Brissie- but are 72 km NW of Toowoomba.

However, I've just taken a look at the 50mm lens I had in and it's got a big black mark on the edge just like the crook 4" one, and the inside edge of the tube is all white where the beam has been trying to obliterate it.
So the alignment is out of kilter big-time.

Mirror one, the beam is 1/4 above centre, but left & right are good.
Mirror 2 on the gantry - the beam is 2/3 to the right of centre, but horizontally it;'s OK.
Mirror 3 on the head- when the beam hits it, it'c centred but it's too high by 2/3.

Time for a cuppa and some clear thinking & realignment- thanks to Scott A for assistance/advice also.

Ian Stewart-Koster
08-02-2017, 8:06 AM
Apologies if my ramblings are tiresome-at least I have a track of what's happening!
Alignments: beam hit close enough to the centre of mirror #1, but was 1cm offcentre of mirror #2- almost partly off the mirror onto the housing, but barely.
IN order to bring it back, I undid the mount screws and moved mirror & mounts #1 wholly closer to the tube. Then aligned it onto mirror #2, and got it centred at both the front and the back of the bed- same spot.

I went to answer the phone, and the light I'd been using to see clearly had fallen over, blew the little halogen bulb, and independently of that the whole laser had shut down. Only the water chiller was still running. The laser does not want to start up or turn on.
Time to have some dinner, and think about it- maybe there's an overload switch or fuse that's tripped in the laser , and blowing the desklamp bulb somehow surged the system?

These things are sent to test us, someone once said...!

Ian Stewart-Koster
08-02-2017, 9:39 AM
No luck.
It will not switch on or boot up.
Maybe the chiller control circuitry has gone haywire and is preventing the on/start button from working? Something is certainly preventing it from starting up.
The circuit breaker in the machine is fine. 240vAC gets past it.
I'm out of ideas right now- and getting just a fair a bit peeved...

Bill George
08-02-2017, 10:04 AM
I am just guessing here, your work lamp fell over and shorted the bulb to the machine. The current fed back to your machine ground but maybe not 100%, the stray current ended up in your electronics and who knows? Check your PC boards for damage a visual insp.

Kev Williams
08-02-2017, 11:51 AM
Emergency stop switch inadvertently get pushed? Circuit breaker?

As for the picture of the lens- the incident beam is clearly hitting the lens WAYYY off center, much of it has been hitting the lens tube, which is why it's hot. How the beam has been centering adequately thru a nose cone is anyone's guess, or maybe it's not and is another reason for the hot lens...

IF you get the machine back up and running, do what it takes to get the beam to hit the center of the lens as close as possible. Even cracked, the lens will still work adequately until you can get a replacement.

This lens in the pic, you can see the 'target' in the middle, this was some guck that melted onto the lens, and that's what cracked it. I cleaned the guck off, and even cracked as badly as it is, the engraving it produces it is no different than from my good lenses. You just need to get your beam towards the center and away from the edge...


Gary Hair
08-02-2017, 12:47 PM
We're not in Brissie- but are 72 km NW of Toowoomba.

I want to live in a place nicknamed Brissie or any place that I can use Toowoomba as a reference for distance/location. Eugene, Oregon just doesn't have the same cool factor to me...

Ian Stewart-Koster
08-02-2017, 8:22 PM
Thank you Kev and Bill.

You'll laugh at this, but yes, when the lamp fell over, and the thing wouldn't turn on, I went right over the machine, looking for circuit breakers that might have tripped due to weird possible stray currents etc - nothing- all in order and not tripped.
So I figured it must be the control circuitry somewhow. I was going to dig out the old CW3000 chiller and plug that in, in case it was a fault in the 5200 chiller control- just to eliminate options.

Somehow I eventually got to the E-stop button, at 1 am this morning and noticed it was looking a bit 'depressed' (almost mirroring my own feelings at the time!). The darned lamp must have clipped it as it fell, and that was the cause. Everything ran fine after that. Whew!

I finished aligning the beam so it lands in the middle of the mirrors at all corners of the bed. That involved actually shifting the mirror mounts M1 & M2 themselves, 10mm & 6 mm, to get the beam parallel to the gantrys/axes, before tweaking the direction a bit. Interesting exercise, but worthwhile. I also had to lift one of the feet up 3mm at the floor - that helped.
The head wasn't perpendicular to the bed either. It is now.

I reran the test ramp, with the 2" FL lens, and found that if I packed 3mm acrylic by 35mm underneath, it was good. But I had to ziptie the airassist hose beside the lens tube, as the nozzle is for the 4" one. The acrylic sweated a lot underneath.

Three things I'm wondering about now:

1. putting the 4" cracked lens back in to retry it now the beam is centred- Kev, you've convinced me to try. Thanks very much!
2. with the lens OUT, the burned test dots on the bed when I was doing the alignments weren't perfectly round, but had a minor flat spot at the left like a balloon sitting on a table. This is unfocused, but I'm not sure where the flat part grew from. (The focused dot is great!)
3. Power... The manual says 28mA is max working current for the original 130w RECI tube, but when I set the software for P=100%, the tube was drawing 21 to 21.5mA, or about 80% of max on my cuts last week and back for 2 months. This is good for the tube's longevity - that's OK.
Last night with my 1.5" test circles, putting P.max=100% & minimum P = 95% in the software, the meter was showing 15 to 16mA draw. not the 21 or so I expected. The cut was finished in about 4 seconds.

Should I be worried?
Does the power rise with time and warming up, eg in a path that might take a minute to cut, as opposed to this which was ending almost as soon as it starts?

I'm most grateful I have a 5 day reprieve on the job - fabricated 3D LED halo-lit letters- I have till next Tues to finish them, instead of having to install tomorrow like originally planned! Thanks, Dear Lord! :)

Ian Stewart-Koster
08-02-2017, 8:26 PM
Gary... some Aussie names are beauties: Woollongong, Woolloomooloo, Indooroopilly, Wagga Wagga, Walla Walla (but I know there's one of them in USA), Gin Gin, Kin Kin, Grong Grong, Mutdapilly... the list is humongous.

But I'd better get back to the laser-it owes me some income, or I'll be in strife!

Kev Williams
08-02-2017, 8:56 PM
I want to live in a place nicknamed Brissie or any place that I can use Toowoomba as a reference for distance/location. Eugene, Oregon just doesn't have the same cool factor to me...

Eugene was cool once :D


Ian Stewart-Koster
08-02-2017, 9:15 PM
I'll report back after I retest the old 4" lens...

Ian Stewart-Koster
08-03-2017, 12:43 AM
Update- the 4" lens wasn;t workling quite right- putting a banana shaped burn on the media, but after rotating the tube it sits in ab out90 degrees, I was able to get it to convert to a fine dot in the middle of the air-assist nozzle, and that nozzle isn't getting hot (so far.)
Spare lens ordered on Fleabay.
3 hours lasering later it's still cool (the air nozzle). I'm stumped as to how the whole thing got out of alignment to damage the lenn in the first place though...

Question: someone told me most cheapish and not so cheapish lenses are actually all the same poorish ones with different price markups, but the 2-6 ones (iivi) are the only true decent quality ones to get.
That sounded plausible.
Opinions appreciated! Thanks.

Jerome Stanek
08-03-2017, 8:56 AM
could the beam have been hitting the side of the tube and heating the lens up that caused the lens to break

Ian Stewart-Koster
08-03-2017, 10:08 AM
very likely

Kev Williams
08-03-2017, 2:35 PM
as for lenses- I don't know the source of the lenses in my Synrad lasers, the Gravograph and the GCC, but the machines are 13 and 12 years old and neither of their lenses have even a hairline scratch or scuff on them. The cheap $20 ebay lenses scratch quite easily. But, I've never noticed the scratches to affect the engraving I do. Might affect cutting, but I don't cut enough of anything to make a judgement... I did recently pick up a couple of GaAs lenses off ebay for about $35, and the one I've been using, and cleaning often, still looks like new. Seems to work okay too. It DOES have a slightly different focal distance, I assume this is because the 'flat' side of the lens is very much concaved, putting the lens surface a snick farther up the lens barrel. But I've been happy with it! The tradeoff is, visible light won't pass thru a GaAs lens, so if your red pointer goes thru the lens, this lens will block it.

Ian Stewart-Koster
08-04-2017, 5:26 AM
That's interesting, Kev.

I had to rotate the lens holder a tad more, to get a better dot rather than a tiny banana-shaped test burn from the cracked lens, and tweak the mirrors in the head a little more also, so it was dead centre below the air nozzle, but I've been cutting 10mm acrylic for about 6 or 7 hours, and the air nozzle is cool to touch, and the beam is clean and fine right through.

I bought a couple of Ebay spares also. This Goldenlaser does not have the red dot, but our little ULS does.
The Goldenlaser software has a 'test rectangle' command, and you press that and it'll trace out the perimeter of the job.
Since the nozzle is only 3mm above the media, its' easy enough to see where it travels and how close it gets to the edges in the test.
(I'm assuming RDWorks also has something similar, for when I strip & convert the machine later on.)

Thanks for your advice on reusing the old 4" lens-it's been a lifesaver!

Bert Kemp
08-06-2017, 11:53 AM
Thanks for the song Kev, been a while since I heard that one, Lov PF. Gary I thought Toowoomba was a cool name too so I did a google earth flybye, looks like a beautiful city to live in. We have some weird city or town names, How bout HELL Michigan, Kickapoo KS,Oatmeal TX how you like to live in NOTHING, AZ LOL Nothing
Town in Arizona

Nothing is an uninhabited ghost town in eastern Mohave County, Arizona, United States. Wikipedia (https://en.wikipedia.org/wiki/Nothing,_Arizona)

Elevation (https://www.google.com/search?q=nothing+arizona+elevation&stick=H4sIAAAAAAAAAOPgE-LUz9U3ME3KKUzXks9OttLPyU9OLMnMz4MzrFJzUsvALADc8sgb LgAAAA&sa=X&ved=0ahUKEwjdvYXZ7sLVAhVB9WMKHU_qCZ8Q6BMIqwEoADAY) : 3,268′

Population (https://www.google.com/search?q=nothing+arizona+population&stick=H4sIAAAAAAAAAOPgE-LUz9U3ME3KKUzX0spOttLPyU9OLMnMz9MvLgHSxSWZyYk58UWp 6UAhq4L8gtIcsCwAxuNdgDkAAAA&sa=X&ved=0ahUKEwjdvYXZ7sLVAhVB9WMKHU_qCZ8Q6BMIrgEoADAZ) : 0 (2008)

Eugene was cool once :D


Jerome Stanek
08-06-2017, 3:44 PM
Another city is Ashtabula Ohio Bob Dylan even used it in a song as he thought it was a neat name.