Another Instance of RA Preload Bolt Failure

Thursday, December 5, 2019 6:05 AM

Problem(s) Encountered:

One of the bolts on the RA preload plate sheared shortly after opening. And then a second. And then a third. Decided to home the telescope at that point and on the way there the
fourth came out and the plate dropped to the floor. This all happened in the span of 45 minutes with not very much telescope movement.

Found all the sheared bolts and washers at least! Including an extra one from the last time (I assume)!


Not as surprising  as unfortunate.  Uncharted waters on how long to go without changing out the bolts.  The roller still walks out over time.  So I monitor and record how far it moves and occasionally jack up the telescope to reseat the roller by tightening up the 4 hardened 1/4-20 bolts.  Still, there is expected stresses on the bolts as the roller walks out, so I also completely change out the bolts from time to time.  That said, I also am interested in seeing how long a set of bolts can last.  Interestingly, I mentioned to Justin earlier this week that he may experience a sheered bolt this week (ok, didn’t expect FOUR).  Jacked up the telescope and installed the preload plate with four new bolts.  Also replaced all 8 Belleville washers.  Slewed the telescope around and all is functioning.  It’s important to stress that this is a bandaid to get us through until we have ample time to tear apart the system and replace the roller with a newly designed one obtained from DFM (we have it in-house).  This may or may not also require a bearings swap—we won’t know until the roller is out and the bearings can be inspected.