Large Binocular Telescope Project

Questions & Answers

concerning the RFP for the

M1 Cells, Bell Jar and Dummy Cell

October 27, 1997

Question 1. (received 2 Oct 97)
Weights of the M1 Cells, Bell Jar and Dummy Cell are missing, can you provide them?

Answer 1. You are correct. These weights are not listed in the RFP documents. The weight of the steel structure of the Aluminizing Bell Jar is 14.1 metric tons. (Our final installed weight on the mountain is 21.2 metric tons.) The weight of steel structure of the mirror cells is 27.1 metric tons.

Question 2. (received 2 Oct 97)
Which bearings and gears for the instrument rotators are being provided by LBT?

Answer 2. Refer to section 1.2 of the Mirror Cells Statement of Work.

LBT is providing the (Gregorian) Instrument Rotator Bearings, but not the instrument Rotator Gears. LBT is providing both the Bearings and Gears for the Instrument Cable Chains. These are to be mounted on the Mirror Cells.

The Mirror Cells RFP mentions the Gregorian Instrument Rotators only. There is a later RFP that will handle the smaller Instrument Rotators in the center section of the telescope.

(Yes, this is a bit confusing to me too, but it is how the history has worked out.)

Question 3. (received 3 Oct 97)
Which is the material for the Mirror Cell structure, Fe 420 B or Fe 420 C ?

Answer 3. (corrected 9 Oct 97)
There is an error in the Technical Specifications for the Mirror Cells and Dummy Cells and the Aluminizing Bell Jar. The material should not be Fe 420 structural steel. The correct material is Fe 430 C --- better in our case according to the welding requirements in the manufacturing phase.

Question 4. (received 17 Oct 97)
What are the dimensional and machining tolerances of the cell and bell jar?

Answer 4. These tolerances are indicated on the individual drawings such as 721a004, 721a006, 721a008, etc.

Question 5. (received 17 Oct 97)
Are the bolts, nuts and adjustment shims for the erection of the cell included in the supply?

Answer 5. The fasteners and shims required for the pre-assembly and vacuum testing of the cells are included in the supply of the cell. This would include the bolts for the various vacuum covers and for the Gregorian Rotator bearings.

The fasteners and shims for the connection of the cells to the Elevation Structure of the telescope are not included in the supply of the cells. Those are included in the Pre-Erection of the telescope.

Question 6. (received 23 Oct 97)
What are the dimensional tolerances for Drawing n. 821a003 (e.g. on the angle of 23.228 degrees, on the positioning of vacuum flanges and so on)?

What are the dimensional tolerances for O-Ring seat and flange (Drawing n. 821a004 and 821a005 detail "C")?

Answer 6. General tolerances according to ISO 2768 / 1-m and ISO 2768 / 2-k (as indicated in the telescope structure drawings).

The seal seats have to be in agreement with the dimension and tolerances given by the seal manufacturer (e.g. see the commercial catalog of Angst+Pfister) A critical surface could be the interface flange between Bell Jar and M1 Cell (internal diameter 8620 mm - external diameter 8910 mm) where is missing a planarity tolerance. Considering that we have the O-ring seal and the locking device to lock each against the other could we suggest 0.05/1000 mm? That means about 0.75 mm on half circumference.

The particular angle "23.228 degrees" of the axis of the flanges on the top of the bell jar is not critical. This could be 23.2 +-0.5 degrees.