Loading ...
Sorry, an error occurred while loading the content.
 

24" vacuum chamber is getting closer :)

Expand Messages
  • James Lerch
    Greetings All, Just thought I d share the initial results on my latest project, a 24 mirror coater :) Today I fabricated the Square O-Rings from stock 10mm
    Message 1 of 3 , Jan 1, 2004
      Greetings All,

      Just thought I'd share the initial results on my latest project, a 24" mirror
      coater :) Today I fabricated the Square O-Rings from stock 10mm O-Ring cord,
      and ran the first leak test (which it failed, but not to terribly bad, I still
      made it down to the 18 torr range on the rough pump..)

      The first interesting part of today was cutting and gluing the o-rings for the
      square openings for the door and base-plate. Cutting the o-rings was simpler
      than I had imagined, I used a wood jig, razor blade, and the trusty hammer to
      make all the 45 degree cuts.

      Next I threw a jig together to hold the two pieces together while I super-glued
      the joints. BTW, super glue and N-Buna o-ring material is simply amazing! The
      glued joint is just a flexible as the stock material and when destructively
      tested, the glue doesn't fail, but instead the o-ring material eventually tears
      away in "chunks".

      Once the O-rings were installed, I hoisted the 400lb beast up and rolled my
      portable vacuum station underneath the chamber, and gently lowered the chamber
      down.

      After running the rough pump for a few minutes I heard that distinct "whistling"
      sound of air leaks, and "Maybe" found an interesting way to pin-point the
      failure. I sprayed white spray paint near the suspect areas. This did two
      things, first the paint was sucked thru the leak leaving a tell tail white paint
      mark inside the chamber for easy repairs, and secondly it actually sealed some
      of the smaller leaks :)

      Tomorrow I hope to weld shut the few leaks that were found and try again! :)
      I'm also thinking that another method for finding the smallest of the leaks
      might be to use some HVAC pump oil that includes fluorescent dye. The hope is
      the smaller leaks will eventually pull the oil thru, and inspecting the inside
      of the chamber with a UV light might reveal their location. Any thoughts on
      this?

      I also shot several pictures of the 'as-is' chamber and moved them over to my
      web-server if anyone is interested. I put together three different file size
      versions of each image, and organized them into their own web-page. Here's the
      links:

      http://lerch.no-ip.com/atm/Projects/Chamber/Small_File_sizes/page_01.htm (200Kb
      Images)

      http://lerch.no-ip.com/atm/Projects/Chamber/Med_File_sizes/page_01.htm (1Meg
      Images)

      http://lerch.no-ip.com/atm/Projects/Chamber/page_01.htm (~2Meg Images)

      Take Care,
      James Lerch
      http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)

      "Anything that can happen, will happen" -Stephen Pollock from:
      "Particle Physics for Non-Physicists: A Tour of the Microcosmos"
    • Dominic-Luc Webb
      ... I note for ultrahigh vacuum copper seals are used. Just a thought. Also, you cannot mean 18 Torr. I presume you mean something like 10e-3 Torr, which is
      Message 2 of 3 , Jan 2, 2004
        On Fri, 2 Jan 2004, James Lerch wrote:

        > Greetings All,
        >
        > Just thought I'd share the initial results on my latest project, a 24" mirror
        > coater :) Today I fabricated the Square O-Rings from stock 10mm O-Ring cord,
        > and ran the first leak test (which it failed, but not to terribly bad, I still
        > made it down to the 18 torr range on the rough pump..)


        I note for ultrahigh vacuum copper seals are used. Just a thought. Also,
        you cannot mean 18 Torr. I presume you mean something like 10e-3 Torr,
        which is characteristic for a common roughing pump.

        I would be interested in your solution for firing up the tungsten
        filaments, presumably you used (green) TIG welding electrodes. I am
        testing this now. I note on your web page you mention wanting to improve
        your heating control. I have built a high power (light) dimmer
        circuit that works pretty well that uses minimal components and is
        dirt cheap (a couple $USD). The thinnest TIG electrodes around here are
        1 mm diameter and about 150 mm long so there is not much resistance. On the
        other hand they are so cheap that one can use 10 or 15 of them in series
        at which point the circuit cold resistance actually increases to sanity
        levels, comparable to a light bulb. My current plan is to get the whole
        series working exactly right and then replace the linear dimmer potentiometer
        (there is also a threshold pot so the dimmer pot changes TIG temperature
        thoughout its entire range) with a switch between two resistance values that
        give either low heat (melts aluminum and wets the electrode) or high
        heat (vaporizes molten aluminum). In other words, the final control unit
        will not have a range of temperatures. It will only have two; melt and
        vaporize. Although, I will keep the dimmer pot as a third setting in case
        I try other adventures (anyone that know me at all knows this is likely).

        If you or some else want the circuit I can arrange this. Basically,
        it uses a BT139 triac (600 V @ 16 Amp) and a diac tuned by a couple
        of resistors and potentiometers that regulate the rate of charge/discharge
        of a capacitor (600 V @ 33 nF) that triggers the triac. Circuit includes a
        filter for radio interference, but this can be skipped because high power chokes
        add signicantly to the price and might not even be needed. I think if you
        get noise you can just as well try turning the potentiometer a tad. I have
        now made a PCB layout and will post the final result on my website when I
        get more time. It is built for 230 VAC mains, but can be adapted for 120
        VAC. I of course welcome any criticism of such a circuit for this application.


        Dominic-Luc Webb
      • Darald Bantel
        Greetings I have been a some time lurker for the simple fact of having not to much to add but today hopefully that could be different. As an employed welder I
        Message 3 of 3 , Jan 2, 2004
          Greetings

          I have been a some time lurker for the simple fact of having not to much
          to add but today hopefully that could be different.

          As an employed welder I would suggest doing something in the opposite
          direction. Apply about 10 pounds air pressure to the inside of the
          system and then spray the weld areas with a soapy water solution and all
          (they are very visible and its cheap too) the pinholes will produce neat
          bubbles whereupon you mark the spots and haul out your trusty welder
          (most likely grinder too) and have another go at making that puppy leak
          free!

          I thank you all for allowing the lurkers to absorb your processes - I
          hope to one day travel the same path!!

          Darald
          >
          > Tomorrow I hope to weld shut the few leaks that were found and try again! :)
          > I'm also thinking that another method for finding the smallest of the leaks
          > might be to use some HVAC pump oil that includes fluorescent dye. The hope is
          > the smaller leaks will eventually pull the oil thru, and inspecting the inside
          > of the chamber with a UV light might reveal their location. Any thoughts on
          > this?
          >
        Your message has been successfully submitted and would be delivered to recipients shortly.