Primary Mirror Handling Procedures

Written by D. Blanco (, G. Poczulp (, and D. Sawyer (
Last Revised on 6/30/00 DGS

Document number WODC 03-22

The following is a step by step procedure for removal/installation of the WIYN primary mirror for re-aluminization.

The hardest part of this procedure is logistics. All activity must take place in a very limited space. Care must be taken to be sure the proper equipment is in the right place and that excess equipment is stored out of the way.

This procedure has been divided into six sections. Each section contains an equipment list, the number of people required and duration, and the step by step procedure. The sections are listed in the contents below and can be accessed by scrolling through the document or by clicking on the title in the contents.



In-Advance Procedures

Removal of Primary Mirror from Telescope

  • Written on 2/22/96 by DRD (

  • Revised on 5/28/96 and 6/30/00 by DGS (

    This is Day 1 of the aluminization process. Some portions of this section require as many as six people. This removal process can be completed in approximately six hours.

    Equipment list.

    1. Remove the Cassegrain instrument, if any. Remove the Modified Cass reimaging optics and add counterweights to balance the telescope.

    2. Remove any instrument from the IAS. The IAS itself can be left on the telescope

    3. Position the telescope at an azimuth of 181d (south). Leave the azimuth brakes disengaged so that slight manual positional adjustments can be made during the next step.

    4. Remove the wooden fillers from the ends of the rails and install the bridge inserts. Be sure the contact points are clean and the inserts seat properly.

    5. Engage the azimuth brakes and disable the azimuth drives. Switch off the azimuth breakers at location 'B'.

    6. Remove the tertiary mirror and the tertiary support structure. This is done with the telescope horizon pointing, so it must be completed before any other part of the primary removal. See Tertiary Mirror Handling Procedures WODC 03-21.

    7. While the telescope is horizon pointing remove the two side panels on the mirror cell that are next to the elevation bearings (see step #12). There are holes drilled in the elevation drive bows to allow access to the panel release screws.

    8. After removing the tertiary stow the Thern floor crane back on the mezzanine level.

    9. Slew the telescope to zenith and allow the primary mirror support forces, pressures, and LVDT positions to settle to the nominal zenith pointing values.

    10. Disable the elevation drives. Install the elevation stay bars (release the brakes to allow the zenith position to be manually adjusted). The stay bars are stored in the southwest dome drive cabinet.

    11. Engage the elevation brakes and switch off the elevation breakers at location 'B'.

    12. Remove the upper access panels to the primary mirror cell and set aside. The panels are removed by turning the screws 1/4 turn and pulling the panel out and downward. The panel must then be slid laterally to disengage the hinge pins.

    13. Prep the mirror for disconnecting:

        Turn off power to the PMS power supplies (location 'B').

        Turn off power to the PMS thermal controller (Utility Room).

        Be sure all cables are properly labeled and uncable the primary mirror cell.

        Close four valves on the fluid lines at the cell near the cable panel.

        Disconnect the fluid lines using a 1-1/2" wrench. Note: A cup or so of coolant will be lost when the lines are disconnected. Install the caps on the fluid lines.

      Note: If you plan to remove the secondary mirror for realuminizing at the same time as the primary, you must replace the secondary mirror with the secondary dummy weight to keep the telescope balanced for the move from horizon pointing to zenith pointing for primary removal. See Secondary Handling Procedures WODC 02-20.

    14. Install braces under the telescope skirt and install the building-to-pier brace on the mezzanine level. To install the building-to-pier brace it is necessary to remove sections of the pier scaffold.

    15. Open the main floor hatch:

        Set the safety railings in place around the floor hatch.

        Lift the two sections of the hatch from the dome floor using the 5-ton hoist. Warning:(1) The hatch covers are NOT balanced about their rigging points so they will pick up at an angle. (2) Watch slings to assure they clear the WIYN port instrument boom.

        Stack the hatch covers atop each other between the stair well and the equipment lift hatch. Place the hatches on cribbing do avoid damage to the dome floor.

    16. Place three sections of 7/8" steel tubing in the west track. Arrange the pieces so that the tube section under the SW hydraulic leg can be removed (so it won't be crushed as the leg lowers).

    17. Rig the lift cart to the 5-ton hoist. Watch slings to assure they clear the WIYN port instrument boom. Lift the cart and place it on the track with the hydraulic connectors pointing north (towards the telescope).

    18. Position the cart so that it is centered under the hoist hook and mark the position of the dome and the cart on the rails for later reference.

    19. Adjust the cups on the lift cart so that they are all equal height. The orientation of the screws should be N-S-E-W.

    20. Push the cart under the telescope.

    21. Remove the rail guide bar under the SW hydraulic leg.

    22. Connect hydraulic lines to the pump unit.

    23. This step may be TBD with the new hydraulic system installed June 00. Lower the cart until all hydraulic cylinders are fully contracted. This raises the hydraulic legs clear of the floor. When the legs reach the end of travel the pressure equalizes in the four hydraulic circuits.

    24. Place spotters at the NE, NW, SE and SW corners of the mirror cell to watch for any interference problems. Raise the cart on power to within about 1 inch of the mirror cell while checking clearances all round. Use the valves on the mirror cart to close off select cylinders to assure that the cart raises evenly Note: Remove the screws in the four cups on the lift cart while lifting to avoid interference with the hydraulic plumbing.

    25. Continue to raise the cart using the hand hydraulic pumps.

    26. The cart contacts the mirror cell at four cups equipped with centration screws. These are also threaded so that they can be advanced by hand. As the cups start to engage make any adjustments needed.

    27. When the cart cups engage the mirror cell legs, continue pumping the lift until the pressure gauges on the cart read about 500 psi. At this point the weight of the primary mirror cell has been transferred to the lift cart. Adjust the cup set screws until they just touch the mirror cell legs.

    28. Insert safety pins in the cart legs to lock them in place.

    29. Using a crow's foot wrench and a cheater bar, loosen the primary mirror cell mounting bolts at the top of each of the flexion bars. This takes two people - one to locate the wrench and spot, while the other torque's on the cheater bar. Warning: the inner bolts are very close to the glass wall of the primary mirror. Place foam padding between the wrench and glass for protection.

    30. Double check that all mirror cell bolts have been removed.

    31. Remove safety pins from the cart legs.

    32. Locate four spotters at NE, NW, SE, and SW corners of the cell. Use the lift cart pump unit to lower the cell from the telescope carefully checking clearances. Continue lowering until the legs lift clear of the floor and the cart is supported by its wheels.

    33. Replace the section of 7/8 tubing in the W track.

    34. Double check the bracing under the telescope skirt, and the building-to- pier brace. Differential expansion can change the settings. Make any adjustments necessary.

    35. Using a winch pull the cart and mirror cell South and align it to the reference marks made when the hoist was centered over the cart. The pump unit trails along behind the cart as it is moved.

    36. Remove the 7/8" tubing from the under the NW cart leg.

    37. Use the pump unit to raise the cart so it is about 2' clear of the floor.

    38. Insert safety pins in the cart legs to lock them in place.

    Removal of the WIYN primary mirror from the mirror cell.

  • Written on 10/20/95 by GP (

  • Revised on 2/22/96 by DRD (

  • Revised on 8/14/96 and 6/30/00 by DGS (

    This is Day 2 of the aluminization process. Four or five people will be required to install the handling band and disconnect the actuators. An additional four people will be required for mirror handling and transport. This step of the procedure will take approximately four hours.

    Equipment list.

    At the start of the procedure the mirror and cell should be located on the handling cart with the top of the mirror exposed to allow the installation of the handling band. The tertiary mirror and cell have been removed.

    1. Remove the three thermocouple sensors that are attached to the OD of the front faceplate by unplugging at the connectors and removing the insulating tape.

    2. Remove the twelve earthquake clips and the two bolts that hold each in place to the mounting blocks using a 3/8" Allen wrench. Be particularly careful of the thin glass side wall of the mirror when using the wrench. Remove one or two of the short PVC ventilation tubes near the lateral constraint devices to allow better access. It will be difficult or impossible to remove these tubes after the handling band is in place.

    3. Record the values of the mirror position indicators at locations 2, 6, and 10.

      Gauge #2 _____________

      Gauge #6 _____________

      Gauge #10_____________

    4. Gently compress the lateral LVDT unit and remove the connecting rod that is held in place between the two detents. Place the rod in a safe place until reassembly.

    5. Assemble the four handling band sections on the floor of the loading dock area. The orientation and positioning of each section is important. Note the cardinal point marked on each section. Install the eight turnbuckles so that the rotation direction for tightening is consistent with all turnbuckles.

    6. On the 5-ton overhead crane, rig the 10K lb. Hydraset with a 1-1/2 shackle on the bottom. Connect four 8' straps to the shackle. Check the straps for any sign of damage. Extend the Hydraset hand controls.

    7. Connect the straps to the spreader bar assembly and raise it through the hatch.

    8. Lift the spreader bars over the handling band and attach the four hangers to the trunions on the handling band. Secure the cover plate by hand tightening the single bolt (do not over tighten). Assure that the orientation of the handling band and rigging is consistent (i.e. all cardinal points correspond). Lift the handling band off the floor and inspect all rigging.

    9. Adjust the Hydraset so that the piston in extended 4-5".

    10. Position the handling band over the primary mirror and rotate it so that the orientation corresponds to the mirror. Assure that the handling band turnbuckles are loose enough to give plenty of clearance for the handling band around the mirror. Slowly lower the band over the mirror with at least four people to guide the handling band into position around the mirror. The orientation of the handling band is determined by the vertical lines on the outer sidewall of the mirror. When the four handling band sections are in place, begin to tighten the eight turnbuckles by hand. Check that the gaps between the handling band sections are uniform (~3 1/4") when the turnbuckles are hand tight. Check that the rubber lining on the handling band engages mirror uniformly and is pulled up so that the rubber engages the top mirror lip. The handling band should extend above and below the mirror by ~0.20".

    11. Check that the crane is centered over the mirror and take up most of the slack in the straps with the crane. Warning: Do not attempt to lift the mirror with the crane at this point. Pump up the Hydraset to 5000 lb. using the hand control only. Allow some time for the straps to stretch.

    12. Remove the single bolt that attaches each of two lateral constraint devices to the Invar brackets at the top and bottom of the mirror using a short 3/16" Allen wrench. If, for some reason, the bolt is very tight, CAREFULLY use a 1" open end wrench on the hexagonal section of the lateral constraint (just to the right of the flexure) to react against while turning the bolt. It is not necessary to remove the entire lateral constraint assembly, but exercise caution when working near them. Place the hardware in a safe place until reassembled.

    13. Disconnect the past zenith mechanism at the bottom of the cell using a 7/16" open end wrench, noting that the preload will be set at reassembly by adjusting the average distance between the washers and the posts that compresses the two springs to 1.64". The connection rods should be left in place hanging loosely on the cell. When the mirror is lifted clear of the ventilation tubes, push in on the rods to drop the mechanism locators to the top of the cell (this happens at a later step).

    14. Under the cell, locate the three hardpoint mechanisms and loosen the 1/8" Allen setscrews that are positioned opposite the index markers. Raise the three hardpoints into contact with the backplate of the mirror by rotating each of the 7/8" hex head screws, using a socket with a long extension, about 1-1/2 turns COUNTERCLOCKWISE. This is opposite the expected sense because the hardpoint mechanism incorporates a differential screw, and one turn corresponds to 0.040". Note the arrow used as an index marker on the flange.

    15. Detach the 66 axial support rods from the backplate of the mirror. This is done by using a 9/16" open end wrench to loosen the locknut (the one on top) while reacting the torque against a 1/2" open end wrench on the support rod bracket. This prevents any twisting on the load cell, which is attached to the support rod bracket. Turn the locknut up to the small diameter on the support rod so that the locknut is completely loose. Loosen the support rod from the puck on the backplate of the mirror by turning the knob (with spanner holes) attached to the support rod. It should turn by hand, but a SHORT handled spanner (7/64" Allen wrench) can be used if necessary. Unscrew the support rod until it drops free from the mirror and rests in the support rod bracket. Mark each actuator with the appropriate numbered tag as it is disconnected. This will allow later inspection to assure all actuators have been disconnected.

      Note that: the lower nut defines the length of the push rod and is a critical adjustment. For that reason it has been lock-tite'd in place. When detaching the push rod, you must use caution to be sure that the nut/knob does not turn on the push rod.

    16. After all 66 axial support rods have been detached it is required that a visual check is performed by looking under the mirror at the support pucks and verifying that all support rods have been disconnected. All 66 numbered tags should be used. It is also possible to perform a check by turning on the active optics system and reading out the values of the load cells.

    17. Install the OD lateral contraining posts at four points around the mirror that don't interfere with the handling band. The posts are attached using earthquake clip mounting holes.

    18. Lift the mirror slowly, USING ONLY THE HYDRASET HAND PUMP CONTROL, to assure that the mirror is not hung up in any way. The load on the Hydraset must not exceed the mirror and handling band dead weight of 5400 lb. by more than 100 lb. It will be necessary to pay particularly close attention to the lateral supports until they are clear of the backplate of the mirror. The three axial LVDTs are spring loaded and do not need to be removed. When lifting the mirror check that the lip on the ID of the central hole in the primary does not catch the lip on the center tertiary mirror support. Drop the past zenith mechanisms out once the mirror is clear of the ventilation tubes. When it is CERTAIN that the mirror is free of the cell, the slow speed on the crane may be used.

      Note: If necessary the mirror cart can be lowered to gain more clearance between the mirror and cell.

    19. When the mirror is clear of the cell, rotate the dome to position the mirror over the main hatch. Lower the mirror into its box on the flat bed truck.

    20. Disconnect the spreader bar vertical hangers from the trunions on the handling band and lift away from the mirror with at least four people stationed at the hangers to guide them clear of the mirror. Secure the mirror in its box by connecting 1/4" eyes to the trunions on the handling band and attaching 1/4" turnbuckles.

    21. Pull the flatbed truck forward into the parking area and install the mirror box cover using the Galieon crane.

    22. Transport the mirror and all rigging equipment to the Mayall Telescope.

    Aluminizing Preparations at the Mayall

  • Written on 8/14/96 and modified on 6/30/00 by DGS (

    This is Day 3 of the aluminizing process. Four or five people will be required to strip and clean the mirror. An additional four people will be required for mirror handling. This step of the procedure will take two hours to unload the mirror and then two to four hours to strip and clean.

    Equipment list.

    At the start of the procedure the mirror should be located in its crate on the back of the flatbed truck. The mirror handling rigging should have been transported to aluminizing area of the Mayall.

    1. Intall the Hydraset and mirror rigging on the 3-ton overhead hoist in the aluminizing area.

    2. Just outside the door of the aluminizing area of the Mayall use the Galieon crane to lift the mirror crate cover off. Note, leave the cover suspended with the crane as it will be reinstalled on the crate after the mirror has been removed.

    3. Back the truck into the aluminizing area and position the mirror crate under the 3-ton hoist with the mirror rigging attached.

    4. Disconnect the turnbuckles and eyes securing the mirror in the crate.

    5. Position the spreader bar assembly over the primary mirror and rotate it so that the orientation corresponds to the mirror and handling band. Lower the spreader bar and connect to the four trunions around the handling band.

    6. Slowly lift the mirror out of the crate using the 3-ton hoist. Once the mirror is clear of the crate, pull the truck out of the aluminizing area. Install the cover back on the crate for outside storage.

    7. Position the mirror so that it is about 80" off the floor. Install safety jack stands at three positions around OD of mirror. Warning: Do not transfer the weight of the mirror onto the safety stands.

    8. Install (9) aluminum whiffletree pucks onto the invar pucks on the bottom of the mirror that have red markings. Install the three whiffletree frames.

    9. Blow off the underside of the mirror and each honeycomb cell using CO2.

    10. Lower the mirror onto the whiffletree stands. Use the Hydraset for the last inch or two of motion to assure a gentle landing. Once on the stands, continue to lower until the Hydraset indicates ???? lb.

    11. Loosen the turnbuckles on the handling band while maintaining ???? lb of pressure on the Hydraset. Carefully lift the handling band away from the mirror with at least four people guiding the band past the mirror.

    12. Strip and clean mirror.

    13. Install handling band, lift off stands. Wipe down wiffletree frames with Ethanol alcohol.

    14. Drive chamber under mirror and lower the mirror onto the chamber deck with the wiffletree frames left in place as mirror stands.

    15. Assemble the chamber, pumpdown, aluminize.

    Installation of the Primary Mirror and Cell

  • Revised on 4/20/98 by DGS (

    This is Day 4 of the aluminization process where the newly coated mirror will be transported to WIYN, assembled on its cell, and installed in the telescope. In general, the procedure is the reverse of the removal process. This step of the procedure will take approximately seven hours.

    Equipment list.

    At the start of this process the mirror will be located in the aluminizing chamber.

    1. Drive the aluminizing chamber deck out from under the chamber into the handling area. Inspect the coating.

    2. Install the handling band and lift the mirror off the chamber deck.

    3. Remove the lid from the transport box using the Galieon and back the truck under the mirror and lower the mirror into the box. Disconnect the spreader bar and raise clear of the box. Note: Be sure Hydraset controls are looped around spreader bars before lifting the band so that they are secured from swinging over the mirror.

    4. Drive the truck out of the aluminizing area and position the transport box under the cover (which should still be hanging from the Galieon). Install the cover and transport to WIYN.

    5. Transport rigging equipment to WIYN ahead of the primary mirror. Assemble the rigging on the 5-ton hoist at WIYN.

    6. Once at WIYN, use the Galieon to remove the box cover in the parking lot. Back truck into loading dock area.

    7. Assemble the spreader bar and lift mirror from transport box. Pull the truck out of the loading area.

    8. Check the adjustment of the dome floor support post on the pier at the mezzanine level.

    9. Adjust the spreader bar assembly so that the mirror hangs level. Raise mirror into dome.

    10. Position the mirror over the cell and slowly lower into position 10" above the cell. Someone should be positioned in the center hole to direct the mirror. With the mirror 10" above the cell, install the past zenith mechanisms.

    11. Continue to lower the mirror while pushing it toward the top of the cell to allow the lateral supports to engage the holes. Stop with the mirror about 1/4" above the hard points.

    12. Connect the lateral flexures and tighten nuts handtight. Apply Permatex 133K anti-sieze compound to the threads.

    13. Check the lateral supports and level with a long pole (i.e. a broom handle) as needed.

    14. Assemble the past zenith mechanisms and tighten the spring to the proper dimension (average distance between washers and compression posts should be 1.64"). Use a 7/16" open-end wrench to adjust.

    15. Set the mirror on the hard points with 300 lbs supported (the Hydraset should read 5000 lbs). Connect all actuators. Many people can be recruited to engage the actuators, but one person should be identified to seat all actuators to eliminate the possibility of missing one and to assure that a consistent torque is applied when seating the actuator. The ID tags should be removed as the lock nuts are seated.

      Note: verify that all numbered tags are accounted for before proceeding. This will assure that all actuators have been connected.

    16. Back off the hardpoints 1.5 turns clockwise. Tighten set screws using a 1/8" allen wrench.

    17. Tighten the screws on the lateral constraining rods.

    18. Remove the OD lateral constraining posts installed at four positions around the mirror.

    19. Using the Hydraset, lower the mirror until ???? lbs is supported by the Hydraset (i.e. pressure gauge reads ????). This is the weight of the handling band and rigging. Remove the handling band and lift away from the mirror. Note: At this point the rigging equipment and transport box can be returned to storage.

    20. Install the earthquake clips and thermocouples.

    21. Install the air nozzles near the lateral support rods and install the LVDT rod.

    22. Use the PMS extension cables (3) to power up the system to measure forces and assure that all actuators operate properly.

    23. Using a winch pull the mirror cart into position under the telescope. Raise the mirror cell into position. Raise the cell to within 2" of the center section. Adjust the bolts on the mirror cart cup pads to align the flexion pins. There should be a spotter stationed at each flexion to measure the progress and assure that the guide pins are engaging properly. The cell should be raised until the flexions are seated against the center section with a positive force (few hundred lbs). Install the four bolts at each flexion and torque to 410 ft-lbs. Use protective padding to assure that the wrench cannot contact the glass while torquing the flexion bolts.The crows foot must be oriented 90 degrees to the torque wrench to obtain a correct torque reading.

    24. Remove any bolts from the mirror cart cups and lower the mirror cart away from the mirror cell and push out from under the telescope. At this point, the mirror cart can be stored below the hatch the the hatch covers installed.

    25. Connect the coolant lines and thermocouple wires.

    26. Install the panels around the mirror cell. Install panel #2 before panel #1. Install 3 and 9 with the screws removed.

    27. Remove the staybars, bridge inserts, skirt jacks and floor post.

    28. Tip telescope to horizon.

    29. Install screws for panels 3 and 9.

    30. Push outer plenum seal around the primary mirror down so that the seal engages the bottom lip of the mirror top plate rather than the top surface of the mirror.

    31. Install the tertiary mirror per WODC 03-21.

    Telescope Collimation and Alignment

    Now that the primary and tertiary mirrors have been installed, it may be necessary to re-collimate the optics. Refer to the document WODC 03-19 Collimating the WIYN Telescope for procedures on how to do this.

    Following verification and/or adjustment of the collimation it will be necessary to re-build the active optics lookup tables. Refer to the "Telescope Operations" documentation available from the WIYN Home page for instructions on building the tables.

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