With a fresh set of expert eyes on site in the form of Brett Shapiro, we embarked on evaluating ETMx in search of the pesky rubbing EQ stop. Having theoretically narrowed the possibilites down to the PUM stage of the main chain, I started by evaluating the bottom barrel stops of the PUM on the right side (SUS convention, looking from reaction chain down the arm). While the stops looked closer than the recently adjusted test mass stops (as was expected), I did not see anything glaring. I then moved to the left side of the suspension and very quickly identified the possible culprit. The bottom barrel stop on the left side nearest the reaction chain was very close to the mass, although not touching in the in-air state (as has been verified multiple times via in-air TFs), it was ~0.1-0.2mm from the mass. I also noted that the lock nuts on neither of the left side lower barrel stops were tight, in fact they were several millimeters from the EQ stop mount bar. We continued to evaluate the remaining bottom-side stops at all stages looking for other possible sources of rubbing but did not find any. As per guidance from SYS/SUS representatives, we readjusted ALL bottom-side EQ stops at the PUM, UIM, and Top Mass stages to the erring-on-the-larger-side of the 1mm spec. We also re-verified that the Test Mass and ERM stops were set to the 1.5mm spec set by Betsy earlier this week. Fingers crossed!
The above narrative focuses on the main goal of the incursion, finding the rubbing source. The step by step checklist summary is as follows:
- Particle counts prior to door removal: 60@0.3um, 20@0.5um.
- Evalutate HR surface of TM pre-work. Nothing egregious.
- Adjusted EQ stops as described above.
- Evaluated HR surface of TM post-work. No noticeable change vs. pre-work. Cursory N2 blow.
- Particle counts in-chamber post-work: 750@0.3um, 410@0.5um.
- Removed tools and stool.
- Particle counts in-chamber post-exit: 140@0.3um, 70@0.5um.
- Took quick TFs of V and P for both M0 and R0 (since both had been touched). TFs look good.
- Handover to door crew.
Betsy plans to run remote TFs on this SUS over the weekend to evaluate it's health on an ongoing basis. Hopefully she will NOT call Kyle's cell!
ETMX