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Thread: XY stability questions

  1. #1
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    Default XY stability questions

    Hey guys, I am using flexure mounts for my dichroics. The dichros are affixed with JB weld. The mounts are bolted to a 10mm aluminum plate. My diodes are securely mounted and my collimators are fixed with a weak threadlocker. Now, I don't do commercial shows so, I am not going from gig to gig with them. I use them for a time and then closet them when I have no time for lasers. When I pull them out again (a few weeks to 1 month later) I invariably have to realign the FF. Generally it is slight, but I can definitely see that the alignment has shifted. Is this normal to have this much drift? I am not sure if it is because of the flexure mounts or the JB weld holding the dichros or if this is just the nature of the beast but I always have to realign. Thoughts?
    Last edited by absolom7691; 07-25-2014 at 19:32.
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    do you align when the system is "cold" (i.e. right out of the closet) or when it has reached thermal stability?
    this could be the reason of your drift
    "its called character briggs..."

  3. #3
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    Quote Originally Posted by LaNeK779 View Post
    do you align when the system is "cold" (i.e. right out of the closet) or when it has reached thermal stability?
    this could be the reason of your drift
    All optics mounts drift over time. Even flexures. Baseplates flex with temperature. Some mounts have steel screws and brass bases, which leads to trouble.

    It takes a lot of engineering to find the right alloy for flexure mounts. My company had to run hundreds of temperature cycling tests to find the right alloy and get the stress relief correct after annealing. All that to get one type of optic mount stable for one year. Which is why our internal cost was 150$ for a 25 mm optics mount. With 20-30 of them in the system, drift needed to be minimized. What was done was to pick a few customer adjustable mounts and install them in strategic places to cancel drift. Usually the first few beam folds are on adjustable mounts. After all, it takes two mirrors or a mirror and a dichro to really set the direction and height of a beam.

    Small, highly stressed, "light show grade" flexures are going to drift.

    Drift is normal. Too much is alarming, and makes me wonder how your base plate is constructed.

    Epoxies have a polymer "relaxation time" measured in months, so usually you want the optic in direct contact with the mount with the epoxy holding it around the edges. Pros use a low outgassing, ceramic loaded epoxy such as Hysol C1 White. The problem with C1, is once its on, well, its not coming off....

    This why we used mechanical clamping against reference points, which is an art itself.

    Steve
    Last edited by mixedgas; 07-26-2014 at 10:54.
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    Quote Originally Posted by mixedgas View Post
    Epoxies have a polymer "relaxation time" measured in months, so usually you want the optic in direct contact with the mount with the epoxy holding it around the edges
    yay!! that' s how i do it, just out of pure luck i guess. great info steve, thanks


    too bad we can' t make everything out of invar
    "its called character briggs..."

  5. #5
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    Quote Originally Posted by mixedgas View Post
    Drift is normal. Too much is alarming, and makes me wonder how your base plate is constructed.
    It doesn't drift very much and it doesn't drift over night. I would say after about a month, instead of white lines, I have white lines with red, blue, or green halo.

    I guess it's just the nature of the beast. Thanks for your input, guys!
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