Azimuth Drive Box Replacement

May 31, 2006

The following procedure outlines how to swap out the azimuth drive boxes. This requires about 12 hrs and 3 persons. It also requires approximately 1/2 night on the sky to tune the drive servo parameters and a pointing model. This assumes the new drive boxes are fully assembled and tested.

Safety precautions such as lock out tag out of the enclosure and telescope motor amplifiers are required. Bump caps are desired when working on top of the azimuth drive ring. Large wrenches required for this work are kept on the Observing level cabinets and tool box. Ensure a complete tool cleanup is accomplished prior to rotating after the new boxes are installed.

A. Start with drive box with soft spring preload Drive #2 .

1. Remove skirting for and aft on telescope
2. Remove enclosure switch collision flags
3. Rotate telescope/enclosure in Az to align opening from skirt removal over the 2 drive boxes. Approximately 115 deg in az. Note: this will cover a small section of 1 floor hatch so if they are required to be used during the shutdown you can reverse the hatches so the left one sits on top of the right and allow hoisting through the left one.
4. Lower 5 ton crane through opening
5. Power off Az amplifiers
6. Install shields over moat
7. Disconnect motor cables
8. Remove Motors
9. Install nylon shims between az disc and earthquake bumpers
10. Loosen encoder preload
11. Place PVC spacer under drive box to hold box once loosened
12. Loosen horizontal foot
13. Loosen tangential link - middle nut 1st , then fwd nut at box, then unscrew from box
14. Install 2- 1/2” eyebolts in box, short eyebolt on link side
15. Connect box to hoist using straps and eyebolts
16. Remove bottom cam followers
17. Loosen, remove bolts from preload caps – do not allow caps to fall out
18. Loosen horizontal foot the remaining amount , push preload foot in to ring and work drive box away from disc. Once clear of disc raise hoist and remove drive box
19. Prep new drive box for installation
20. Transfer lower foot . Note: new boxes use fine thread bolts on lower cam followers. transfer eye bolts. Place short one on proper side
21. Wipe down drive disc and drive capstans
22. Lift new box in place - do not contact drive disc with box
23. Extend preload foot and tighten, slightly keeping alignment with disc and foot
24. Connect tangential link and set alignment using drive box to disc clearance and foot centering as metrics
25. Extend bottom foot to support weight of box, remove PVC spacer
26. Install bottom cam-followers
27. Tighten horizontal foot and tangential link nuts
28. Adjust bottom cam followers so they "just" do not touch the drive disc

B. Repeat previous instructions for second drive box

C. Setting the preload/level

1. Tighten horizontal foot with hard spring until shims between disc and earthquake bumpers are the same tightness as before starting
2. Set preload at soft spring by extending the horizontal foot until the soft spring compresses all the way (wrench will get very tight)
3. Back off 1/4 turn
4. Check shims again for proper tightness (same as above) , If no change – remove shims
5. Check level , use precision level. Check drive axis first then idler axis, adjust by extending/retracting horizontal foot at the hard spring boxes. Take readings by rotating level and averaging to compensate for level error. Always approach desired position on horizontal foot from same direction- compressing preload
6. Reset encoder preload, tighten until springs compress (wrench will get tight) then clean drive disc upon completion
7. Using hand crank in place of motor check, rotate telescope in each direction, check and adjust box preloads as necessary for smooth operation, no slippage, and easy movement. Repeat for each box.
8. Install motors , recheck cam followers to ensure no top bottom pair are tight, remove moat covers
9. Power on amplifiers
10. Reinstall collision switch flags and skirting, test skirting does not touch floor, stow 5 ton hoist
11. Test at 50 mc.go then 100, 200, 400, 500 in both directions, watch dataq, listen and watch for slipping
12. Remap az (manually trip end of limit switch)
13. Run TCC slews