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  1. #21
    Join Date
    Dec 2005
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    484
    No, not really a link...I mean I guess you could, but then they would have to register here to see pictures..and that pisses some people off.

    Put the pictures up on another site, or post them to a binaries newsgroup, or the metalworking dropbox...that is a good idea...post em to the metalworking dropbox and then post your question on alt.lasers. Google "metalworking dropbox" for the link.

  2. #22
    Join Date
    Jun 2005
    Posts
    1425
    KTP - I've now established a page to view any laser photos(cnc ones later, hopefully)
    at www.fanmaker.co.uk/lasers.html .
    I'm now staring at the tube in an effort to see inside it, and wondering if I'll have the nerve to take it to pieces.
    On the subject of different modes. I pressume that in a bad set-up there will probably be several modes active at any time, so the final output is a mixture. Thus the pattern is more complicated than the 'simple' patterns that are illustrated for the different individual modes. Have I got this right ?
    Otherwise, will the pattern that my burns show indicate some sort diffraction caused by crud on the oc lens ?
    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.

  3. #23
    Join Date
    Jun 2005
    Posts
    1425
    More photos of oc end of tube.
    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.

  4. #24
    Join Date
    Jun 2005
    Posts
    1425
    I've now progressed to taking the output end assembly to pieces, having identified that there is an air gap through the tube inboard of it.
    (see bottom of page)
    Todays pictures show the current state, but I will probably take the assembly out later today, as it appears to be only held in place by two screws.
    www.fanmaker.co.uk/lasers.html

    Assembly now out and inspected - ugh !
    Drawn my idea of the optical path, so I must now decide where exactly the surfaces are, and do I need to remove them in order to clean them.
    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.

  5. #25
    Join Date
    Dec 2005
    Posts
    484
    Yes: Rotary Solinoid

    No: Heater

    The "heater" is actually a (carbon coated?) temperature sensor used to measure the power output of the tube when the solinoid rotates some metal or optic in place to reflect the beam into the sensor. This also acts as a safety solinoid to prevent output when certain interlocks, etc. are not triggered.

    Is the OC optic (the one on the end of the laser tube) really dirty? Can you see any adjustment screws yet?

  6. #26
    Join Date
    Jun 2005
    Posts
    1425
    when you refer to the oc optic I pressume you mean the output lens/mirror of the actual lasing cavity. In my case that would seem to be inboard of this rotating solenoid.
    I assume this, because there is no gas seal outbord of it.
    What is dirty is the last face of the outermost znse optical component which is also the half-silvered reflector for the HeNe beam.
    I'll post the photo and drawing I've made here.
    Both of the surfaces I've drawn are contaminated, and if there are additional faces that I haven't found yet, they too may be in the same state.
    No sign of any adjustments for the main optics (HR +OC) yet.
    Attached Thumbnails Attached Thumbnails assembly2.jpg   output assembly drawing.jpg  
    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.

  7. #27
    Join Date
    Jun 2005
    Posts
    1425
    Here's one of the "solenoid". I hadn't thought of the "heater" actualy being a sensor. That would make more sense(sorry ) than my idea.
    Attached Thumbnails Attached Thumbnails OC view 3.jpg   solenoid coil spring.jpg  
    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.

  8. #28
    Join Date
    Dec 2005
    Posts
    484
    You can safely remove the two optics - the one that reflects the hene at 90 degrees and the one that combines the hene and the CO2 laser beam. Keep the sensor (thing you called the heater) and the rotary solinoid in place. Now measure power output and see if things have improved.

    I still think your output mirror (OC, output coupler) is dirty and misaligned.

  9. #29
    Join Date
    Jun 2005
    Posts
    1425
    Another photo of the inside of the solenoid and heat sensor. This part is beginning to make sense thanks to all the input from various sources.

    The solenoid will have a 45 degree mirror firing the beam down onto the copper mesh. This scatters the beam safely onto the heat sensor to give a meter reading for the beam power. Pressing the beam output switch will rotate this mirror out of the way, unless other safety interlocks prevent it.
    (Itallics = theory)

    I'll try firing it up again tonight once I've got the arm clamped down. With no aiming beam I need to know exactly where to put the target.
    Attached Thumbnails Attached Thumbnails power measuring.jpg  
    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.

  10. #30
    Join Date
    Jun 2005
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    1425
    Having repeated the burn test, with the HeNe alignment assembly removed, I find there is an obvious increase in power hitting the target but the pattern of multiple beams, though slightly different, is still apparent.

    The beam power readings on the meter are still in the same range, being limited to about 7 watts maximum.
    Varying the gas inlet needle valve does have an effect, moving the power reading up and down, but by very little.
    The power control knob will take the reading down to zero, but turning it up, the increase is inconsistent, even dropping slightly during rotation.

    So now I have to look at removing the solenoid assembly ?
    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.

  11. #31
    Join Date
    Jun 2005
    Posts
    1425
    Solenoid removed and new photo shows an end cap apparently with a znse plate(?) inside it.
    Behind this is a single socket cap screw, not three as I was expecting. So still no sign of any adjustments.
    To get a better view of this I think I shall have to remove the large knurled ring I've labled "power assembly ring".
    This appears to hold the power assembly body in place onto the main beam tube, and should slide off, over the end cap.
    Is it possible that there are only adjustments at one end, HR or OC ?
    Or is this unheard of ?
    Attached Thumbnails Attached Thumbnails Beam output cap.jpg  
    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.

  12. #32
    Join Date
    Dec 2005
    Posts
    484
    Hmmm, maybe that knurled ring is actually something you rotate to adjust the OC somehow...or maybe when it is turned, three screws will be revealed in the holes and they are used for adjustment...just guessing here.

    I think that ZnSe "plate" is actually the OC...not much else it could be. Is it really dirty?

    I guess there *could* only be adjustments on the rear mirror (HR), but that would be a bit weird.

  13. #33
    Join Date
    Jun 2005
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    1425
    That ZnSe plate seems absolutely clean. Difficult to get a good view, but with a dental mirror and a magnifier, I couldn't see anything on the surface.

    One other thing now puzzles me. It seems to be a very complicated procedure to set up if you have to take this "power measuring assembly"(henceforward PMA) off before each attempt at adjusting the alignment, then to reassemble it all before checking the result of your adjustment.

    Access to the HR end does seem a lot easier, so perhaps I should switch my attention to that end before disturbing the OC end. Especially if, for the moment, I can't see any surface problem.
    I have got a stereo microscope in the attic which I could set up to look down the into this oc end ZnSe. But I can already see a mirror surface a little way in, so I'm not going to get far inside.

    Interesting idea of the holes revealing the adjustment screws - I'll have a look. I'll also mark the current positions of all the rings before moving anything.
    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.

  14. #34
    Join Date
    Jun 2005
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    1425
    Both rings have now been removed, but no sign of any adjustment screws.

    I have also removed the inner end cap at the HR end, photographed it, and replaced it. What is exposed may be a plain mirror, but I'm not touching it at the moment.

    A better look at the ZnSe "plate" does show some deposits on the inner face - tiny spots with secondary zones around them. One is central, and there are several others scattered around but with no pattern to their positions.
    My first thought was that the central one was a pit caused by the main beam, but all the others look the same, so I think they are all deposits.

    I wil try and draw them over the weekend - photography might be problematic - and compare their distribution with the burn pattern.
    A set of small Fresnel lenses ?


    The single visible socket screw located behind the "plate" has a wire running inwards to what appears to be the end of a 1.5 turn metal tube - earthing electrode ?
    There is an air gap between the end cap and the "plate", but the plate turns with the end cap when I rotate it, so it must be sealed to it in some way.
    It could be just an o-ring which is sticking them together. There is an o-ring at the HR end, inside the end cap, and which presses the mirror(if that's what it is) onto the main tube.

    Is it possible to built a laser tube with no adjustment screws ? Two concave surfaces pressed against perfectly parallel faces of the tube ends ?
    Attached Thumbnails Attached Thumbnails OC end cap.jpg   HR end cap removed.jpg  
    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.

  15. #35
    Join Date
    Jun 2005
    Posts
    1425
    I can now say that the 720 has no adjustment screws.

    I've taken the end caps off, and can see from one end of the tube to the other.

    As soon as I can get a better photo I'll post it, along with a photo of the crud encrusted OC !

    The ZnSe "plate" is just that - no curvature on either face, the inner one with a coating, so I've now got to wait for a supply of non-residue acetone.
    Attached Thumbnails Attached Thumbnails open end cap of laser.jpg  
    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.

  16. #36
    Join Date
    Jun 2005
    Posts
    1425

    Update

    I've just finished polishing off the crud from the OC with a slurry of talc and glycerin.
    To cut a long story short, instead of removing the reflective surface along with the crud, it has now improved the output of the beam to 12 watts.

    However, I'm still getting a series of hot spots instead of a single beam, but if focused with a 200 mm znse lens, it punches a neat hole through wood veneer.
    Headway, but I'm not there yet.

    Current problems - the gas bottle has to go back to the owner next week, so I'm still looking at alternative sources for gas mix.
    Someone on alt.lasers has suggested catalytic converters as a method of controlling the purity of a recycled mix which is an interesting idea.
    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.

  17. #37
    Join Date
    Oct 2005
    Posts
    96
    Hi greybeard,

    Three months has passed, is the problem solved?
    Or the patches of black images still there?

  18. #38
    Join Date
    Jun 2005
    Posts
    1425
    Hi coleong.
    Thanks for the interest.
    Unfortunately a major medical problem put everything on hold for a while. Since then, I'm glad to say, my wife has recovered.
    However, the CO2 laser is still in its original condition, needing a new set of mirrors in the tube.
    I'm also rethinking my whole approach to the idea of using this sort of set-up, rather than investing in a sealed tube.

    Lots of pros and cons to be considered in both systems, but I think the only way forward with the Sharplan is to come up with a recycling gas system. Here in the UK the cost of setting up the gas bottles with a commercial supplier is prohibitive for the diy experimenter. There's a DIYlaser group on yahoo from which I picked up a lot of ideas in this direction, but many other projects and interests have kept the laser cnc at the bottom of the current list I'm afraid.
    Regards
    John
    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.

  19. #39
    Join Date
    Oct 2005
    Posts
    96
    Hi greybeard,
    It's good to hear that your wife has recovered,send my best regards to her.
    Sorry that i do not know so much on the sharplan, but from my judgement the mirrors (OC and rear mirror) are not line up properly.
    Thats way the power is low and there are patches when you burn the paper.
    As per the gas mix,if you get it from BOC the gas used is of high purity.
    If you will to mix your own you'll has problems like low laser power in the short term and damaged mirrors from contamination from the gas in the long term.

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