Ikenoue, Simon, S. Saitou, Akutsu (in Mitaka on June 1, 2018)

Background

With the results here, we reworked the suspension wires of the NAB so that the distance from the IF base's bottom to the center of the NAB becomes the nominal value (710 mm) + longer.

Before reworking, the ruler can read the center is 571.5 mm and the top lim of the NAB was 171.0 mm, which are consistent with the desgined NAB diatemeter 800mm. The bottom lim of the NAB was not able to be measured as it was too low. Note that those numbers are just raw number read from the ruler attached to the assembly frame by heading downword.

Eventually the measured value of the distance from the bottom of the IF base to the center of the NAB was 703.5 mm, while the nominal number should be 710 mm; so it is too short, and thus we determined to shorten the wires.

Shortening the wires and balancing

When we decided new wires' lengths, we take into consideration the desgin limitation of the vertical adjuster; it is hard to lower the whole suspension including the NAB rather than raise it. At first, we elongated the wire length +7mm each (actually, at that time, we thought the nominal distance should be 709mm, but now I checked by myself and that should be 710mm!). But using the new wires, the NAB tilted in pitch; and the resultant distance 707 mm was still shorter than our expection. With several measurement, we learned this center hight cannot be explained only by the pitch mislaignment; this would be due to the inbalance of each blade spring from which the wires come.

As a second trial, we tried to further elongate one of the wires more + 4mm! But still the center hight move was less than our expection. Then we tweaked the adjusters for aligning the NAB to compensate the pitch misaligment. At the same time, we found the NAB was about to touch the EQ stop in the longitudinal direction, so we also tweaked the whole suspension to make distance btwn the NAB and the EQ stop properly. After these works, the measure distance became 712mm, which matched the requirement "710mm" + alpha.

Anyway, we need to do the similar works when we bring the NAB to the actual frame in Kamioka.

Other notes

• During the work we found the assembly frame itself was obliqued, which should be resolved in the first stage of the assembly, and this issue was put into the A/I list.
• Probably tuning the wire lengths is too tough to repeat; using ballast masses would be better.