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Thread: You get what you pay for. Galvos that fail!

  1. #1
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    Default You get what you pay for. Galvos that fail!

    So it started out innocently enought. Its snowing here in Ohio, and we're socked in.
    I'm in between jobs, I will be starting a new one soon. No more X-rays, I'm back to lab lasers if the paperwork goes through. The choice was clean up the lab, or play with lasers. So I dug out the driveway, using a snowblower that had not ran in a year. It started on the first pull.

    I have a gig coming up in a week, and I'll need to run a abstract generator. Its the client's gear, so nothing is critical, except me getting some practice in. So the order of the day yesterday was to dig out a dead Omni 150 PSU from the pile and fix it. I then got out a 532 head that had not ran in 3 years. I'd never even ran it, since I bought it. It started on the second pulse, no Oudin coil needed. Swapped out a 488 only OC, and Voila, 8 lines of violet through blue green. Why? Abstracts just do not look good in DPSS green.

    So today I look at the 5 choices of scan heads in the storage pile, and pick a "Quality Asian" product out of the pile. I had my choice of Asian, Eye Magic, and Cambridge, and open loop. Well, I want a small system as I'll need to rent a little place between here and the new job. So the the Eye Magics can stay in Prometheus II, the main projector. Prometheus is 38" by 18" by 18", and has a six position beam table. Its designed for dual external ion lasers or a fiber from a KTP.

    The Cambs have never been matched to the amps, they came from different vendors. A quick check of a certain chart showed I would need to change three caps and two resistors on the amps, and I did not have one of the cap values in stock. Ok, Cambs are next week's project.
    Besides, they have red only mirrors on them, hardly fit for a Argon, and I did not feel like dicing mirrors, either.

    So its "Chivo" time. This particular set has less then 20 hours on it.
    The scan head has been setting in a sealed box in a nice cabinet in a basement that stays between 55'F and 70'F year round. First thing to do was to make a nice 36" extension cable.
    So I could put the amps in a nice rackmount case I have laying around, the idea being the PCAOM driver and amps could fit in a SK rack case, which would be aquired from the local surplus place.

    So two hours of delightful cable design and construction. I make Mil-Spec cables when I'm not in a hurry, and the "weather outside was frightful". Besides I need the soldering practice, for the new job. So the dual cable gets made, Gotta love 20 year old rolls of rosin core, has that great old flux smell. And it works.

    Now we're getting down to business. I could practice my abstracts on a vectorscope. I also have a program that lets me view them in near real time using a sound card. But I have a lot of 457 from this old, yet new, tube. Plus, when you scan analog abstracts, the scanners have "Bounce" when you adjust the console. It looks different in laser then on a CRT or LCD.

    OK, Twenty year old analog console, not used in a year, starts right up. (See a pattern here?)

    So the scan head comes out of its wood box. Craft stores sell these nice wood boxes, with latches, cheap. Women like their trinket holders to be of quality, so these are a steal.
    They keep the parts from rusting, too.

    Hum, whats this? I touch a galvo mirror with a swab. Its stiff. Good galvos "flop" when they are not powered up. Ok, this has happened once before, so once again I will gently grasp the shaft with pliers wrapped in cotten and slide the mirror around. Lubricants do get stiff.

    Ok, but that did not work so well. Its rock solid. So is the other one.
    Deep sucking sound, as I contemplate tossing them in the trash.

    So I try a little more torque. Drat, off comes the mirror, the epoxy crazed and failed, the mirror is fine. Now, I am from the school of "Never Say Die". After all, I make my living with 1949 and 1970s technology. New high tech stuff gets made with old Cold War era stuff. Trust me on that. I fix old stuff, in order that others can research new stuff. I'm good at it.

    So I pop off the Sensor covers, two screws. I gently press on the inner sidewall of the ball bearing with a probe. Its flimsey, caves inward. NOT GOOD. Worse yet, its bone dry.

    Dad, Requiescat in Pace, was a diabetic, and hated needles. He went out of his way to get the ultrafine needles, as they are less painful. So when he passed, I kept a few of the needles. Now don't get any ideas, these are too fine and too short to reach a vein. They are, however, tiny enough to reach around a position sensor flag and get the lubricant in the right spot.
    So I'm thinking microlitres, if not nanolitres. Wrong... The bearing just absolutely sucked the oil up. All 4 bearings in the pair sucked the oil up.

    OK, the mirror is off, so its hardball time. I apply massive torque, and the shaft breaks free.
    With some "exercise" I can feel the lubricant start to travel and the bearings slowly start to work.

    So I improvise a mirror mounting kit, and I epoxy the mirror back on.

    I managed to lube and loosen the other shaft.

    So I go and check the other galvos. EMs are just fine. The Cambridges, have not been used in years, and they just flop with gravity. All the GSI stuff, well, no issues, and no need to check.

    My Point? A two year old unused pair of Galvos, from what is perhaps the best Asian maker of clones, should not have dry bearings, nor a lubricant that evaporates.

    I have 20 year old GSI G120s, that are ready to go, right now.

    Something is wrong with this picture.

    Ask me how they scan tomorrow. I know they will need some retuning. After all there is no chance that I grabbed the correct viscosity of oil. They now have Toy status.

    Moral of the story.... You get what you pay for.

    Next week the Cambridge amps get converted, I cannot depend on these clones. Ceramic, sealed, aviation grade, bearings are clearly worth the extra Dollars.

    Steve
    Last edited by mixedgas; 02-11-2012 at 22:02.

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    Wow, that's not cool. At least you had a couple back up sets. Out of curiosity, who manufactured the set? From what you said, it seems like you are refering to the DT's, but I haven't heard of a problem like that from the DT's. I've seen a couple unique failures of the DT's though, a snapped rotor was the worst of them.

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    Quote Originally Posted by DZ View Post
    Wow, that's not cool. At least you had a couple back up sets. Out of curiosity, who manufactured the set? From what you said, it seems like you are refering to the DT's, but I haven't heard of a problem like that from the DT's. I've seen a couple unique failures of the DT's though, a snapped rotor was the worst of them.
    Yep, Delta Tangos.

    Steve

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    Post edited for a while

    Steve[/QUOTE]

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    These things happen. When I bought my Jeep brand new the water pump failed after a few weeks due to a bad bearing. On the other hand, my LaserPic scanners that I paid $225 for many years ago still work like a champ despite the abuse of sitting around un used, being fed random terribly out of range when experiments go bad with my software, and having my kids use my scanner window for a My Little Pony house (a mirror broke off but the galvos are fine). So, yea, it's easy to say you get what you pay for but an isolated occurance doesn't mean they are all that way. Interesting story, though. And I know how much it sucks to drag out a bunch of stuff when you want to tinker and then something that SHOULD work doesn't. At least you are resourceful and can plow ahead.

  6. #6
    mixedgas's Avatar
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    Scanner 1, OK.

    Scanner 2, oscillates on 1 out of every 4 power up cycles from stop to stop.
    There is no stop per se, its the position sensor flag hitting the case.

    Further analysis indicates the applied oil from the upper bearing made it into scanner 2's rotor area. It has just enough drag to force the amp to max peak current when it causes friction.

    The limiter circuit is not engaging on the board that oscillates. The LM3886 heats up quickly.

    I thus cannot ever advise oiling a scanner, as expected.

    Steve

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    I have some old (maybe) 20k galvos. one has a shaft sticking problem.
    I thought about using http://www.amazon.com/Hoppes-Precisi...=pd_sim_auto_3
    To it and see if i cant fix the problem.
    Every time before i use them i have to tap them.
    Its not a huge deal but i wanted to use it for my laser harp and i dont want to have to poke the galvos every time.

  8. #8
    mixedgas's Avatar
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    If all your doing is harp, would you like to try a G124 open loop? Will never stick, in fact it will never die.
    I have 25 year old ones that act new. Speed limit is 12K, but the angle is great.

    Steve

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    sounds interesting i only need 1 amp and galvo.
    whats the cost of one of those things?
    Im not sure i need a large scan angle but might be nice.
    Also if i wanted to try would that lube i posted be okay for galvos?

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    Quote Originally Posted by mixedgas View Post
    Yep, Delta Tangos.

    Steve
    I wonder if these were the older dt-40's or the newer dt-40pro's? The older dt's had an epoxy issue, I had a set that failed as well, very similar symptom the rotor was bound up pretty good. The pro's use a better epoxy and shouldn't have that problem.

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