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Thread: creating custom shaped mirrors?

  1. #11
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    That's impressive shape. I think vapor aluminum is the only way to make that unless you make it from glass and silver. Silver will stick to nickel so maybe plate plastic with nickel and then silver. Pure guess. I don't see the aluminum stating on the Mylar as it's stretched into tha kind osevere shape. I was thinking more of a one axis parabolic type thing. For focusingnot diverging.

    Again shapeways in aluminum or stainless and polish it yourself.


    Quote Originally Posted by mxandy View Post
    How does plastic mirror change the weight of a mirror if theres still glass in the front protecting the mirror film?

    check this image for mirror shape
    https://i.imgur.com/Iktw4oK.png

    Only info I could find about thermoforming mirror plastic was this where it says thermoforming mirror acrylic/plexiglass specifically is not posssible, but not sure about mylar or other plastics. I don't see the aluminum on a shiny mylar suddenly turning into dust and falling off no matter how hard a pull and bend it unlike a more rigid plexiglass with metalized aluminum film on it so it might work. Never thought how that worked, probably transparent film covering both sides of the reflective film?
    https://www.theplasticshop.co.uk/pla...hop_manual.pdf

  2. #12
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    People use heatgun on mylar for making it shrink and become flatter. https://youtu.be/YpdqJDtjwLo?t=1m41s
    Sadly theres very little info on this. Maybe, just maybe if I glue mylar to a rigid ring but have it somewhat loose, then put itover an existing shape I can remove the excess mylar bulge/wrinkles via a heatgun like this? If this works I'll need to keep the existing shape in place permanently but it can be made from thermoformed ABS easily.

    The polished aluminum approach noted, but again since Ill probably need to make a dozen of these during prototyping I'm hoping of finding some more info on the other possible options first.
    Theres also one company I found which thermoforms mylar on bulk order so it must be possible, and since heating it up to shrink it doesnt damage the reflectivity since people make flat mirrors that way maybe thermoforming reflective mylar will also work unlike reflective coated Acrylic which is much less flexible.
    That said on one hand I see people heat up mylar to cause it to shrink then I see a company which heats (for thermoforming) mylar to stretch/reshape it so this is a bit confusing.
    Hope to get a response from them soon.
    Last edited by mxandy; 09-25-2017 at 01:54.

  3. #13
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    While I'm waiting for the test results from one company on how successful vacuum forming a reflective coated mylar is I found like 5 other companies which state they can do vacuum forming of mirror coated acrylic/plexiglass, mirror HIPS (high-impact polystyrene) or reflective mylar.
    1) https://www.youtube.com/watch?v=BPnJaeBXC4k&app=desktop , http://www.protechmodel.co.za/
    2) http://www.acrylic-online.co.uk/mirrored_acrylic.php "The mirrored acrylic can easily be vacuum formed,"
    3) http://www.delviesplastics.com/p/Cle...lic_Sheet.html
    4) http://www.visionsinplastics.co.uk/P...on%20Info..pdf "It can also be vacuum formed to a limited extent."
    5) http://www.plasticstockist.com/High-...ene-Sheet.aspx , http://"https://www.amazon.co.uk/Sil.../dp/B00GMGX3PA Can be easily vacuum formed, making it the ideal material for a whole range of point of sale and point of purchase applications, signage, sports equipment, make-up trays and craft application."

    So I emailed all of them and will post when I get a response.
    Worst case scenario all are full of shit or forming causes the plastic to stretch too much and become semi-opaque and so less reflective (my goal is at least 80% reflectivity).

  4. #14
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    I have one last thought. Can you coat the acrylic with silica and the deposit silver on it like a regular mirror?

    http://www.sciencedirect.com/science...4060900101046X Liquid phase deposition of silica gel on plastic.

    Now your surface should take a silvering. I'd try silver get the plastic direct. It should work. You might also be able to do it to the thermoformed Mylar as a second coating to fill in the gaps.

  5. #15
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    Correct me if I am wrong but from what I have read silver on plastic even if possible has few downsides or maybe even show stoppers. I'll list what I've been told below, correct me if I'm wrong:

    1) silver has non-uniform reflectance across the visible color spectrum
    2) Unlike applying silver to glass and using the opposite side of the glass as a mirror in which case the glass acts as a protective layer using the other side exposes silver to humidity and other factors which make it dull.
    3) Unlike the glass side the other side will still require polishing to get a mirror finish so why even bother with plastic plus silver rather than pressure formed aluminum sheet and polishing that?

    On a side note I can't find how good chrome is as a reflector. Anyone has any data on this?

  6. #16
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    Got an email reply from the first company in the list, protechmodel.co.za/
    They hadn't mentioned what material they use and I had only seen a video.

    It's "chrome vynil film" and I don't know how good that will be as a mirror.
    Googling it shows its widely used on cars and the thinner sheets can be formed by hand pressure and a hair dryer/ heatgun.




    Will post responses from others using other materials when I get them.

  7. #17
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    Might work. Have to stop thinking and try at some point. I'm taped for ideas.

  8. #18
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    Can you break your material selection into prototyping phase and production?
    For prototyping it shouldn't matter as much if the surface is perfect or durable, you need to see if the shape is correct yes?
    The mylar emergency blankets and other thin films soften under heat -- they were originally stretched at the factory and held taut while cooling so when you re-heat them they do shrink a bit, but you can also stretch them yourself over a form or with air as you suggested. That might get you through shape testing.
    Then once the shape is chosen you can look at materials for production.

  9. #19
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    Thank you, I did not know that. If I can pull it over a shape to get a form I need I could attach it to something to keep it over that shape even when its cooled. Do you think that will work? I'm currently building a heating box covered in aluminum foil and an ordinary heater placed on the bottom and also just had a vacuum former machine parts CNC cut. I could use the heater box to heat mylar and test it out. Do you have any idea what temperatures I should be aiming for? I bought few polycarbonate, HIPS, PETG and acrylic mirrors to see if they can be thermoformed. I also bought a chrome vinyl film used on cars and some reflective mylar. Waiting for these to be shipped. I'm hoping the plastics will vacuum form without cracking the mirror films. They definitely can be thermoformed but I have contradicting info on the thermoformability of these plastics after they are metallised. But I can always thermoform clear polycarbonate, HIPS, PETG, acrylic or just ABS and pull a heated mylar sheet over it if none of the above works.

  10. #20
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    .005'' Duralar mylar film seems to work. I didnt vacuum form myself but got someone to send me a sample and it seems very reflective after being formed as well, although the stretched parts are translucent and you can clearly see lights through it. This makes sense as the aluminum particles are farther from each other now. Haven't done a reflectivity/power loss test but for my specific project mylar for prototyping seems fine. I've also gotten few 1mm first surface mirror HIPS and PETG sheets. Those are easy to vacuum form. Not sure if it will be any good and worth the time spent, maybe the aluminum coating on the plastic first surface mirrors is denser than with mylar, or maybe not and it will too become translucent. What do you guys think, worth a try? Alright, now that I have a way to get me a custom shaped mirror the actual fun part starts. My goal is to make a short throw video projector from a normal pico projector with two mirrors. Any hints what shape the two mirrors should have? With lenses its easy to visualize in my head, mirrors are a bit confusing, maybe because I've never done this before.

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