Problem pquest SNF 2009-06-08 12:25:16: Variable air leak--only OK for O2 etching

shott at shott at
Sat Jun 13 08:37:06 PDT 2009

Elmer, Jim Haydon, and Cesar have replaced the ferrofluidic seal with the equivalent model from Rikagu 10C-11099402 (FD-CF-0250-F)
which is a chemically resistant model.  This uses a fomblin base for the ferrofluid rather than the normal hydrocarbon base.
In the process, Elmer and Jim decided to remove the gear drive and modified brackets for a direct drive approach.  This will, hopefully, reduce/remove lateral torque from the feedtrhough and will extend it's life.
The up/down motion now drives very silently.
In the process of repairing this, the motion of the wafer arm also stopped.  This was disassembled and we found that the toothed gear on the threaded drive shaft had loosened to the point that it was only slipping.  Also, the connection on the end of the ferrofluidic rotary feedthrough had been "grooved" by slippage of the shaft coupling to the motor drive.  Repositioning that shaft coupling, retightening all couplings an pulleys, and re-aligning the chain drive have returned the drive to service with nice, quiet performance.

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