NOTE - THESE NOTES ARE SOMEWHAT OLD, LEFT HERE FOR REFERENCE. THE NEXT TIME THE MIRROR IS REMOVED, ROCK-CLIMBING STRAPS SHOULD BE USED BOTH TO LOWER THE CELL TO THE FLOOR WITHOUT USING THE CART, AND SHOULD BE USED TO PULL THE MIRROR OUT OF THE CELL WITHOUT USING THE TRIPOD OR THE CENTER PLUG. A STRING HAS BEEN LEFT IN THE CELL TO ALLOW STRAPS TO BE PULLED AROUND THE MIRROR. 3 SETS OF TWO 44" STRAPS TIED TOGETHER ARE USED FOR THIS PURPOSE. THE STRAPS CAN BE REMOVED BY LIFTING UP ON THE JACKPOINTS, WHEN REINSERTING THE MIRROR.
ITEMS NEEDED:
Tripod (in warehouse)
Cart (in warehouse)
Box - built
Box cover
Transport box to 60"
Hoists and buckets (instruction manual)
Shackles, slings and caribiniers, need to buy slings per Meeks spec.
Two pallet jacks to move the box around (Get one from MMT)
Lifting plug
Secondary box (in chart room, remove old secondary)
Check chain + strap lengths - should allow cart to reach floor
Need 18 wood wedges 1/2" by 1" square
PROCEDURE:
(1) remove secondary, put in box. A rope, or blovck and tackle needs
to be used to hold the mirror up while it is being unscrewed, as the
assembly weighs around 50 pounds. The three innermost bolts, with hex
heads are the ones to unscrew. The earthquake stops must be removed.
The mirror is detached from the assembly via the three allen head screws,
once these are out, the mirror may be wedged away from the assembly
(the triped that is RTV'd to the glass stays with the glass). Keep
track of the belvel washers.
(2) remove stovepipe and corrector
(3) remove counterweight on top ring, replace with restraining rod clamp
(4) install restraining rods (kept on upper level). First do dec rod,
the shorter rod, with
telescope at horizontal position, tweak Dec motion until ball at end of
rod seats in the clam (the other end is bolted to a square shaped bracket
on the polar axle near the north pier, use a large open end wrench and
a large screw driver which holds the nut in place).
Bring scope to zenith and install
RA rod, one end goes on main counterweight arm, the other on the eyeloop
on the north pier, about 4 feet off the floor.
(5) loosen worms on both axes.
(6) remove earthquake stops
(7) remove all mirror covers so that the struts will clear the covers when
the cell is lowered. These are unique, so make sure the numbers on the doors
are legible.
(8) remove instruments and back plates of cell
(9) detach finder, tie to telescope at the top, remove electronic boxes
(10) remove spring loaded radial hard point
(11) undo radial counterweights. This requires that the counterweights
be removed, so that the ball joint pins may be unscrewed from the
pads. There is a special wrench for this task, called a crows-foot.
Remove the screw that pins the rotation restraints. This is done
from above the mirror, using a ball driver.
(12) Remove pins from axial coounterweights. This can be done
by lifting the mirror up on the jacking points a bit.
(13) remove all 3 jacking points
(14) undo Lou's spring restraints.
(15) hook up chain hoists and cart, double chain the hoists, use enough
strap length to allow hoist to reach floor. Put hoist handle on
the bottom near cart.
The two short yellow straps are placed around the trunion at the
NE and SE corners, carabiniers connect them to the chain hoists. The long
straps are placed around the trunion on both sides of the dec axis. Two
4x4 and one 2x6 blocks of wood are used on top of the trunion to make the
distance come out right.
(16) Place a several small piece of plywood at the center of the
cart, Attach hoist hooks to cart, and raise it the cell
(17) unbolt cell, tape shims to struts so we don't lose them
These bolts have only 3/4 of thread, so there isn't much screw.
(18) lower to floor, with tripod underneath, mirror sticks out of
cell. Mark mirror location w.r.t. cell.
(19) Place one long yellow strap around SE upper truss, and another
at NW truss, connect with looped pink straps, and attach one of
the hoists at the juncture, which is now in the center of the
telescope.
(20) Put plug in center of mirror. Lift mirror. remove cart and tripod.
(21) move box underneath the mirror, lower mirror. leave plug inside
(22) seal box and ship with secondary and mirror rotation jig.
Reattachment
Watch radial hard points as they might be clipped off when reinstalling
the mirror.
Use straps as above to lower mirror into cell. Don't use the plug any more.
Mirror must be realigned in same orientation roughly. This can be done
by attaching plumb bobs to the axial hard point pucks on the mirror
(or the axial counterweight pucks) and lining them up with the hard
points on the cell. Also may want to use wooden wedges to shove mirror
into place.
Set centering after mirror is fully in.
Must rotate cell on cart back to where it started, or check alignment of
cell with struts by using plumb bobs, perhaps the cart itself can be
moved.
Occasionally have to bend struts to get them to mate to the cell bolt
holes.
Replacing radial actuators is a pain. Must remove at least one bolt on
the bracket attached to the cell to help screw in the ball-joint pins.
It also helps to remove the weights from the rods before attaching the
rods.
The spring retention system is tricky. The spring/bolt assembly must be
totally taken apart to reinstall. First, screw bolt into puck which is
attached to mirror, the short thread side goes in - a nut is threaded here
to stop the bolt. Then place the bracket next to the cell (note that one
bracket is bigger than the others since the holes are different sized).
A large washer comes next, followed by the spring, followed by a small
washer, followed by the nut. The idea is for each spring unit to have
40 pounds of force. The purpose of that is to pull the primary back down
on the hard points, the mirror having been floated by the axial counterweights.
The hard points themselves are spring loaded, so to much force is also
a bad idea.
See the memo by Lou Boyd for explicit instructions.