Prism alignment
Last Revision:  Oct. 11, 2006
JB

General Comments:

This describes modifications to prism alignment proceedure, since  now we are mounting without the CMM. 
Since the prism sees a parallel beam, optical tolerance is loose, compared to other optics.  We're going to
try to mount the prism without the CMM, but if we find that we can't hit the required tolerances, we can
always go to the CMM and finish there.

Requirements: 

• The prism support pads must be positioned along the midline of the prism sides. 
• The prism must be centered with respect to the cell rotationally around the z axis.
• The tolerance for locating the pads on the prism in terms of  mechanical  requirement of the cell holding the prism by the center of mass is 1 mm.
• The tolerances for locating the pads on the prism in terms of optical requirements are
• +/ 0.075 mm in each of x and y
• 0.05 degrees for x tilt, y tilt and rotation around z axis.
• .075 mm = 3 thou inches;  .05 degree rotation amounts to 5 thou or 0.12mm at edge of prism
  

Supplies:

• 2216 epoxy
• EC-1945 primer
• 3901 primer
• supplies to mix primer, epoxy
• gloves
• acetone
• chem wipes
• RH meter
• grid
• thin lead pencil w/ compass
• ground wire bracelet
• respirator
• file to roughen invar
• jigging to hold prism and cell while curing
• guide to hold pads out when placing cell on prism
• .005 inch tape for epoxy layer
  
• calipers, scales, dial indicator, rulers

Preparations:

• Clean sides of prism with high grade acetone.
• Roughen invar pads where they will attach to prism.  Be careful not to bend them.  Clean thoroughly with acetone.
• Rough align cell on jig.
• handling of prism:  use gloves, two sets of hands when lifting.
• Before applying primer, test align prism on grid, check tolerances.
• Level and test turntable
• Clean all items
  

1.  Primer: 

•      Must be done no longer than 24 hours before application of epoxy. 
•      Must have > 30% RH, get RH meter from 5th floor.

2.  Primer prism:

•        use 3901
•        one part, so no mixing
•        use any disposable brush to apply
•        30 minute cure time
•        primer witness glass
  

 
3.  Primer invar pads:

•        use EC-1945
•        this is explosive -- use respirator, ground wire, hood
•        2 parts, mix each part first
•        mix both together --> green
•        use camel hair brush to apply
•        overnight cure time
•        primer witness metal
  

4.  Alignment of prism
    a.  on turntable, place prism on grid
    b.  align prism rotationally on grid. 
         determine thickest and thinist points (rotation and/or caliper)
    c.  mark 3,6,9 o'clock on side of prism, near face that is down.
    d.  flip prism over
    e.  align prism rotationally on grid
         determine thickest and thinist points
    f.  mark 3,6,9 o'clock on side of prism, near face that is down
    g.  draw line between marks on each side of face (in pencil)
    h.  bisect line, using compass technique
    i.   remove marks except cross which aligns with holes in pads
    j.  Put prism on jig and align cell with it (line up 3 crosses with 3 holes)
    k.  When lowering cell onto prism, use plastic sheet guide, since pads
         are a little undersized.
    l.  review tolerances

5.  Epoxy prism
    a.  use 2216
    b.  2 part exoxy, mix by weight (5 pts base, 7 pts accelerator), or volumne (2 parts base, 3 parts accelerator)
    c.  use syringe and squirt into holes.
    d.  thickness is .005 inches: use tape or shims to maintain proper thickness
    e.  apply pressure with rubber band ring
    f.  2216 working time:  90 minutes from mix
         cure to handling time:  8-12 hours
         full cure: 7 days

6.  Witness samples
     a.  make thin (like real layer) and thick blobs on tin foil thingie
     b.  glue a piece of glass on a piece of metal with primer?

 7.  Cell and Earthquake mount assembly
    a.  assemble rest of cell
    b.  measure earthquake mounts, bend ends
    c.  clean and paint earthquake mounts
    d.  epoxy to use:  Q3-6093.  find on bookcase in 3rd floor lab. 
         This is a sample from Randy Lutz, who has lots more.
          Mix 10:1 by weight, not volume
          Need to borrow vacuum pump from Mirror Lab to pump down
          Has very fast working time:  30 minutes
   e.  Check with Brian Cuerden about thickness, extent of epoxy