QUAD 04 BUILD 03

Today the latest Build of QUAD 04 was completed by Jeff B. and Andres R.  This work signifies the transition of "QUAD 04 BUILD 02" to "QUAD 04 BUILD 03".  The following is an excerpt from an email sent by Jeff Bartlett on 11/10/2011 to members of the LHO SUS group explaining the mechanical adjustments made to QUAD 04:    

   "We removed shims from the Reaction chain to correct optical viewed 
roll and fix optical viewed and ruler measured height. There are now 
zero shims on the left blade and 3mm of shims on the right side. The 
test masses for both chains are sitting at 21mm. This agrees with the 
optical level. I did not think the effort was worth the reward for a 
0.5mm height change. The optical lever shows a slight bit of pitch 
differential between the chains. However, as I will discuss later this 
measurement is suspect.

    There is differential yaw between the masses at L2 and L3. The 
measured yaw at L3 is almost zero in relationship to the frame. I trust 
this measurement because the frame gap is set by the 5mm spacing plugs 
and the frame is ridged at this level. The measured yaw for L2 is all 
over the map. To tune this out will result in the yaw at L3 going out of 
spec. Perhaps it was the wrong decision, but I though the gap at L3 was 
more important than at L2.

    There is still side shift between the two chains, which has been 
reduced but is not gone. The side shift, of around 1mm, is the most 
egregious at L2, but is still visible at all levels. We can tune it out, 
but doing so induces out of spec yaw problems at L3 and L2. We have used 
almost the entire swing range of the top stage blades to get it as close 
as it is. I believe this same problem was observed at LLO, although I 
don't know it's final resolution.

    Above I alluded to a lack of trust in the optical lever (laser 
reflection from mirrors attached to the centers of L3 masses) 
measurements of pitch and yaw. This mistrust comes from the surfaces 
machined into the faces of the dummy masses. The manufacturing 
tolerances for these masses are not that tight and misalignment between 
the dummy mass halves are known. Although these are small, they do not 
lend themselves to accurate pointing of the target mirrors. This is not 
as bad on the M0 dummy mass (D060355) because the center is drilled out 
and the mirror sits on a small shelf. However, on the R0 dummy masses 
(D060358 and D1002204), where the centers are solid, there is a bump 
left over from machining, right in the center of the mass. This bump is 
large enough to miss align the mirror by a considerable amount. On the 
Quad-4 R0 dummy mass, we removed as much of this bump as we could and 
used 0.010" shims as standoffs in an attempt to true the mirror. With 
this, we were able to put the bubble within the circle of the level but 
could not center it. As a result, yaw does not reflect true to the face 
of the mass. Pitch looks OK but not is certain. "

                                                 -Jeff Bartlett on 11/10/2011