With Hirata-san, Fujii-kun and Fabian.

Yesterday and today:

• Hirata-san and Fujii-kun assembled the metal mass.
• One Sol-Black-coated socket-head screw lost a bit of coating in the center of the socket, apparently due to the use of a ball-head hex wrench. They replaced the affected screw with a spare and successfully tightened all the screws with a flat-ended wrench.
• We cleaned the mirror box with the airgun and ethanol-soaked wipes and oriented it on the work table as it will be immediately before installation on the trolley system, with the bottom corner of the box to -Y.
• We transfered the metal mirror to it, with the thick side of the wedge towards left = +T = -X.
• The PEEK feet supporting the mirror in the box were at suitable places not to line up with the large holes, and just tall enough to prevent the raised section around the glass mirror from touching the baseplate (there was about 2 mm of clearance). 
• We checked the thickness of the prism at the thickest and thinnest points: 98.9 mm (exactly as per the CAD) and 90.2 mm (cf. 98.9-2*pi*250/180 = 90.17 mm).
• We checked the lengths of the prisms - they were both 20.0 mm.
• We aligned the metal mass in yaw using the lens system and installed the prism jig stages, prism jigs and primary (sapphire) prisms. We used sapphire prism #3 on the left and #4 on the right.
• We did a check of the heights of the prisms. The distances from the highest and lowest points on the "AR" face down to the prisms were 40.9 and 32.0 mm, implying distances from the "AR" side of 38.0 and 38.2 mm. The desired value is half the average thickness less half the prism length, or 37.275 mm.
• We decided to correct for this discrepancy by adding 0.7 mm washers under each of the PEEK feet. This gave "AR"-to-prism distances of 37.1 and 37.2 mm, which is much better.
• We repeated the alignment with the lens system (because we'd had to remove the metal mass temporarily and because Hirata-san realized that earlier one of the lens units had not been pressed in the right direction against the locating pins).
• We put the metal prisms in the jigs and checked that both sapphire and metal prisms were well-aligned with the barrel of the metal mass.
• We added the mirror box lid and the magnet jig holders.
• We installed the magnet standoffs in the magnet jigs, using long standoffs on the thick side of the wedge and short ones on the thin side, with N poles at top left and bottom right, and S in the other corners. We tried a new convention where the notch in the jig will always face the thin side of the wedge on the mass (right = -T = +X), so the slight compensating wedge on the bottom of the standoffs should have the high side nearest the notch.

The metal mass is now ready for application of EP30, but we decided to tackle that tomorrow morning.