RA Drive Preload Plate Bolt Sheered

Saturday, June 22, 2019 11:04 AM

Problem(s) Encountered:

At around 1:15 we slewed the telescope to near zenith to rotate the instrument.  Once there, one of the screws of the RA drive preload snapped in half and flew out of its hole along with the washers. We've since recovered the half screw and all three washers. Decided to close up rather than risk further damage. Couldn't hear anything in the small movement to the telescope stow position...


Jacked up the telescope and brought the roller back into place using the 3 remaining bolts.  Then replaced all 4 bolts with new ones, iterating bolt-by-bolt, turning each by first 1/4 turn, then 1/8 turns until all 4 bolts were tight (and evenly torqued as well as I can do by hand).  Brought the weight back down on the roller and checked the dial indicator.  Slewed around in both directions a number of times then brought back to zenith and checked the indicator again.  Roller has walked (settled) into position with a displacement of 0.017”.  That is on par with what I was expecting.  Clearly, this is a bandaid on a much bigger issue.  One that will be looked into this summer, possibly (hopefully) including on-site support from DFM.