LBT- Interface Mechanical


  • Beam clearance: 80mm from primary mirror edge
  • Mount points co-planarity: 1-1.3mm (0.040-0.050")
  • Mount points flatness: 380-640um (0.015-0.025")
  • Mount points surface finish: 1.6-3.2um (63-125uinch)
  • Height difference of lower and upper mount: 0.3mm


Shim and plate tolerances as recommended by T. Hair 2010.10.27:
  • coplanarity = 1-1.3mm (0.040-0.050")
  • flatness = 380-640um (0.015-0.025")
  • surface finish = 1.6-3.2um (63-125uinch)
Requirements on Gear as of T. Bluemchen 2010.11.09:
  • Tilt on Harmonic Drive gear: 1.43arcmin (derived from the Permissible dynamic Tilting Moment and the Moment Stiffness).
  • In-plane alignment: 1.0arcmin
  • results in delta hight tolerance: 1.0arcmin
  • results in lateral hight tolerance: 0.6mm (for 2173mm bearing distance)
  • split to all components result into different hight: 0.3mm


Bob Meeks 2010.11.04:

No shims are used.

The co-planarity is guaranteed with a fixture. (TBD: Hinge line is given with upper I/F-Plane, this has to be measured and MPIA need to give a tolerance on it, when is it no more possible to compensate with the SwingArm - focus, tip compensation)

The lower plate would then be attached to the telescope using bolts through the structure with backing plates as previously proposed and a Dynamold castable shim material will be used to ensure solid contact with the c-ring extension arms. The lower plate would be machined with the 1.6 micron finish you desire but the upper plate would be as-is, a 3.2 micron finish.


  1. argos_lbt_interface_upper_mount.jpg
  2. argos_lbt_interface_shimming_position_gauge.jpg
  3. argos_lbt_interface_Mounts_incl_hight_2010_11.jpg


  • Position
  • hole pattern


2010.12.02 Bob Meeks suggested to change the hole pattern of the lower mount because they have been quite close to the stiffening ribs inside the LBT structure.

  1. argos_lbt_interface_lower_mount_distance_stiffening.jpg
  2. argos_lbt_interface_lower_mount_distance_stiffening_topview.jpg

Drawing left before change 2010.11.17 and drawing right after change 2010.12.14.

  1. argos_lower_mount_old_227-01-04-01_V02_drw_101117.jpg
  2. argos_mounts_lower_part1_227-01-04-01_V02_drw_101214.jpg

2. Vignetting of primary mirror

2010.02.18 Joar Brynnel confirmed agreement of 80mm clearance around primary mirror.

Specification: 80mm ~ 0.5 deg radius

Design 2010.11.10 (most right drawing): 74.44mm (Not fully met, but to be verified with LBT CAD model, which is more recent!! )

  1. argos_lbt_interface_primary_vignetting_top_view_details.jpg
  2. argos_lbt_interface_primary_vignetting_top_view.jpg
  3. argos_lbt_interface_227_v01_101102_rest1_02_Dist.jpg

3. Upper interface plane measurement

Bob Meeks 2010.12.02 stated that a measurement will take place 15 December.

Evaluation still to be done (05.05.2011)

4. Fixture, hole template and ground plate

  • MPIA will design an produce a large drilling template with upper an lower mount included
  • This will be also used for shipping of the full assembled swing arm
  • LBTO will provide the fixture for gluing
  • AI: LBTO has to provide some position for threads to screw the fixture and drilling template together

5. Confirm optical axis with LBT model

Telecon 28.04.2011
  • Alignment of telescope optics known to ~1.5mm accuracy.
  • Measured on Hubs and Primary with tracker target.
  • Mount pad measured to pins in primary mirror cell.
  • Agreement on another measurement in early June late May
  • LBTO will compare it with current CAD provided to Thomas Hair by MPIA
Topic revision: r3 - 07 Aug 2018, AndrewColson
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