IRCAL (Dis)Assembly Instructions
or: "How to take it apart and put it back together without having any extra
pieces left over."

   By James Graham, Marshall Perrin, and Jamie Lloyd.
   [1]IRCAL Disassembly
   [2]Optics Changeouts
   [4]IRCAL Re-assembly
   [5]Appendix - Taking apart the filter wheel box
IRCAL Disassembly

   Remove IRCAL from the AO bench. Be sure to use a grounding strap while
   disconnecting the cables, and IMMEDIATELY attach the preamp grounding
   plug to the preamp. Make sure the window cover is closed to prevent
   inadvertent fingerprints.
    1. Crack vacuum
    2. Flip dewar so that it rests on its handles
    3. Remove 16 9/64 screws on base and dismount base.
    4. Withdraw the base vertically so as not to snag the G-10 dog
       clutches It's nice if you leave on the waveplate/flexure metrology
       system bracket, which provides a mechanical reference when
       reinstalling it.
    5. Stow the base and cover with kim wipe. The o-ring should come off
       with the base.
    6. Remove 3/32 first radiation shield screws
    7. Remove 8 G-10 tab screws, being careful not to scratch the o-ring
       mating surface withthe screwdriver
    8. Remove 8 feed through screws. Remove the first radiation shield by
       lifting up on the G-10 tabs.
    9. Remove 3/32 second radiation shield screws and remove the 2nd
       radiation shield, again lifting by the G-10 tabs.
   10. You now have access to the optics
IRCAL Optics Changeouts

  Changing Apertures
   First disconnect the home switch wire by unplugging the small black
   connector partway along the wire. With a long hex driver, unscrew the
   three 7/64 screws which attach the wheel base to the optics table.
   Lift the mask mechanism out, being careful not to snag on the baffle
   tubes. Any mask may be replaced by loosening the beryllium copper
   clips and popping out the mask. Insert the new mask and re-tighten the
   To reinstall the aperture wheel, just slide it back into position and
   re-attach the screws. It helps to have someone hold the mask wheel
   properly aligned as you screw it in. If the aperture wheel is placed
   where is naturally sits, the feedthroughs rub on the shroud. To
   prevent this, hold the aperture wheel with a stiff clockwise rotation
   before screwing it down.
   Specifications: Aperture masks must be 0.995" in diameter, 1/16"
   thick. Plate scale at this focal plane is 34.3 microns/detector pixel
   = 454 microns/arcsec.
  Changing Filters
   Removing the filter wheel is somewhat complicated. In order to lift it
   clear, the light baffle clamp on the front side must be loosened and
   slid away from the filter wheel box. Then loosen (but not remove) the
   box containing the final camera optics, and move it slightly away from
   the filter wheel box. After that is done you should be able to unscrew
   and lift up the filter wheel mechanism. The rear baffle on the filter
   box interlocks with the rear optics baffle box, necessitating that
   filter box it tilted so the baffle tube can be disengaged.
   Individual filters are most easily changed via the access hatches on
   the filter box. By twirling the motor drive shaft with your fingers,
   you can rotate the appropriate filter into the aperture. Filters are
   held in via small beryllium copper clips, which can be removed via a
   small screwdriver. (Just loosen the clips enough to rotate them out of
   the way. This make it far easier to get them back into place after
   inserting the new filter.)
   In order to see the filters in position, you will have to slide the
   cold pupil up out of the way. **Be sure to put it back down into
   position when done** Doing this is a useful way to check the
   orientation of grisms or prisms.
   See Appendix for a discussion of actually taking the whole mechanism
   Specifications: Filters or holders should be circular, 1" in diameter.
   The 2nd filter wheel accomodates thick elements up to 1/2" thick. The
   2st wheel only accomodates filters less than ??? thick.

   While it's open, you might as well change the getter. Unscrew the box
   containing the getter, dump out the old stuff, and put in new pellets
   from the huge jar which is on the shelf in the instrument room. There
   are two different kinds of getter, so replace each with the
   appropriate same type.
   The charcoal getter doesn't wear out unless it becomes contaminated.
   The zeolite permanently adsorbs water unless it is baked at extremely
   high temperatures. Given the small size of the getter charge, it
   pretty easy to just replace it. The charcoal is really messy, so best
   to leave it alone.
IRCAL Re-assembly

    1. Reverse 9-4. If any screws fall down between the dewar and first
       radiation shield, the easiest fix is to flip the dewar and gently
       shake it until the screw falls back out.
    2. Clean edge of dewar wall where o-ring seals with isopropyl
       alcohol. Clean o-ring and groove. Apply a thin coating of vacuum
       grease. Reseat o-ring
    3. Align G-10 cubes in the dog clutches and lower the base. This step
       is made much easier by first aligning all the dog clutches and
       cubes in the same orientation, e.g. with their sides parallel to
       the sides of the dewar.
    4. Tighten the screws 1/4 of a turn at a time, rotating one side at a
       time so that you uniformly apply pressure on the O-ring. If the
       outer dewar wall were to become tilted with respect to the dewar,
       the o-ring can pinch.
    5. Check for positive engagement of the motor feedthroughs by
       confirming motor motion. You can see the aperture mask moving by
       looking in the window, and you should be able to feel/hear the
       home position engage.
    6. Put back on the final outer dewar walls.
    7. Connect the pumping manifold to the pump using stainless flexible
       hose. Include the convectron vacuum guage using a T-piece. Make
       sure that the o-rings are free of dust and debris. Do not
       over-tighten the clamps. With the dewar valve closed pump down the
       fore line to a few mTorr (should take no more than a minute). If
       the line does not pump down promptly check the seals. When the
       fore line is fine open the dewar valve slowly (10-20 seconds to
       open). Leave the dewar pumping with the valve fully open for at
       least two hours at < 10 mTorr. Valve off, disconnect the fore line
       and begin cool down.
    8. To cool, use the white plastic funnel connected to the long narrow
       metal tube. Insert this *carefully* into the opening on top of the
       dewar, being careful to insert it vertically so as not to puncture
       the sides of the heat exchanger which are apparently quite thin. A
       cardboard box of the appropriate size may be used to prop the
       funnel up so its bottom is only about 1" inside the reservoir,
       which will make the fill *much* faster.
       Get LN2 from down in the basement near the CAT room. Pour the LN2
       into the funnel and wait for it to drain out and boil off. Repeat
       this procedure until it stops boiling off inside of IRCAL; the
       pattern of escaping gases will change noticably at this point so
       it's not hard to tell when this is. You can also monitor the
       cooldown by connecting the temperature controller and reading out
       the internal thermocouples.
Appendix - Taking apart the filter wheel box

   This is a potentially disasterous step because the filter wheels are
   spring-loaded and held in place by several hundred very small sapphire
   ball bearings which could easily be spring launched all over the room.
   Doing this is not necessary during normal operation or filter changout
   but may be required to repair broken home switches or make other
   repairs inside of the filter box. **Do this only after carefully
   understanding the assembly drawing.**
   In order to open it safely requires two people. Place the filter wheel
   box horizontally on a table, with the removable side facing up. It's
   irregularly shaped so you will want to support it using some small
   flat objects like kimwipe boxes etc. One person should, by hand, hold
   the two pieces of the filter box together, while the other person
   unscrews them. Only once all of the screws are removed should the
   first person *slowly* release pressure on the top piece, allowing the
   springs to lift it up and away from the rest of the filter mechanism
   slowly and without everything flying apart. The top side can then be
   lifted off carefully by hand, exposing the wheels and other mechanisms
   inside. *DO NOT* unscrew the filter wheel shaft (which is the central
   machine screw on one side, and looks very tempting). The removable
   side is the other one.
   Putting it back together requires a reversal of this process. In order
   to put the removable piece back in place, the wheels and springs have
   to be compressed. One trick that works well is to hold everything
   together by applying downward pressure through the open aperture hole
   onto the wheels, compressing the springs that way and allowing
   everything to be fit back together and screwed into place.
    [6]Elinor Gates
   Last modified: Tue Feb 4 11:11:30 PST 2003


   1. http://mthamilton.ucolick.org/techdocs/techref/ircal/ircal_assembly.html#dis
   2. http://mthamilton.ucolick.org/techdocs/techref/ircal/ircal_assembly.html#optics
   3. http://mthamilton.ucolick.org/techdocs/techref/ircal/ircal_assembly.html#getter
   4. http://mthamilton.ucolick.org/techdocs/techref/ircal/ircal_assembly.html#assem
   5. http://mthamilton.ucolick.org/techdocs/techref/ircal/ircal_assembly.html#append
   6. mailto:egates@ucolick.org