With Shoda-san and Fabian.

Today:

• We started to debug the payload mass issue from yesterday but encountered a second mystery: the RM-optic EQ stop screws in the bottom of the RM were so far off-center to +Y in the slots in the bottom section of the security structure that they were touching.
• After some investigation we discovered that Fabian had been much too enthusiastic yesterday afternoon when operating the jack under the -X,-Y corner of the BF. The pushrod had run out of range and had started to lift the BF ring as well as the BF. This tilted the whole security structure and moved the bottom section in -Y.
• We lowered the jacks to a level that was in range for all of them and checked for other problems. Apart from a bent clamp that had been holding down the IM ring, everything was OK.
• We measured the pitch frequency of the payload (with the optic locked to the RM). It was around 0.4 Hz, which is about what we were wanting. Shoda-san suspects that a big fraction of the mass that we took off in the last few days was added in error because we ended up close to her original design, which has most of the ballast mass on the bottom. Indeed Fabian had added extra because Hirata-san's measurement of the IM said it was too light by 400 g relative to the CAD. In any case, we appear to be almost exactly where we want to be.
• We routed the cables through the flying saucer cable clamp, but not yet through the hex cable clamp on the bottom of the BF, because it hadn't been installed.
• We remeasured the position of the rod relative to the edge of the BF ring and found it was now central to within 1 mm.
• We remeasured the position of the IM with relative to the EQ stop brackets around it and found it was central in Y and off by only about 1.5 mm in X.
• Some of the off-centering in X was obviously due to a slight roll of the IM (lower on the -X side), so we moved a 33 g disk from the -X,+Y corner to the +X,+Y corner to compensate.
• We adjusted the height and centering of the yoke.
  • For setting the height (the PEEK coil form should protrude by 6 mm above the baseplate) we found it was convenient to use a 6 mm hex key as a reference. (It's difficult to get a ruler close because of interference from the keystone safety ring above.)
  • For setting the centering, we found it was convenient to insert the short arm of a 3 mm hex wrench between the inner and outer coil formers, at three positions 120° apart (a 3.5 hex wrench would have been better, but there's no such thing in a standard hex wrench set).
• We installed the hex cable clamp on the bottom of the BF.
• We checked that we could move the keystone over the full range of the LVDT (Shoda-san was worried that we might have to remove the BF again for LVDT calibration.)

Tomorrow we hope to route the cables through the hex cable clamp, tweak the total mass if necessary, calibrate the LVDT, and test the picos.