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SinglePoint Diamond Turned Technique

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Use a single-crystal diamond cutting tool to accurately turn the ... Grooves scatter and diffract light. Limits the application of SPDT technique in infrared ... – PowerPoint PPT presentation

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Title: SinglePoint Diamond Turned Technique


1
Single-Point Diamond Turned Technique
  • Ping Zhou

2
Outline
  • Introduction
  • Materials
  • SPDT Machines
  • Surface Figure
  • Surface Finish
  • Post Finish
  • Advantages Disadvantages of SPDT Technique

3
Single-point diamond turning
  • Use a single-crystal diamond cutting tool to
    accurately turn the surfaces to finished
    tolerances
  • SPDT technique (1960s)
  • Linear axes position feedback resolution 8.6nm
  • Rotary axis encoder angular resolution 0.25 arc
    sec
  • Mostly in IR application due to the surface finish

Computer controlled cutting tool, monitored by
interferometer
Vacuum chuck
Spindle with air bearing
4
Materials
  • Materials that are not diamond-machinable
  • Silicon based glass and ceramics, steel,
    beryllium, titanium, molybdenum...
  • Diamond-machinable materials
  • Metals
  • Alluminum 6061, copper, brass, gold, nickel,
    silver, tin, zinc
  • Polymers (molecular length and elasticity)
  • Acrylic, acetal, nylon, polycarbonate,
    polystyrene
  • Crystals
  • ZnS, ZnSe, Ge, CaF2, Si

5
Two basic types of SPDT machines
  • Lathe type
  • Work piece rotates diamond tool translates
  • Axisymmetric surface
  • Off-axis optics
  • Flycutter type
  • Diamond tool rotates work piece translates
  • Flats
  • Multi-faceted prisms

6
Surface figureradius of curvature irregularity
  • Radius of curvature
  • Typical tolerance for radius of curvature 0.05
  • Relatively short radii limits of spherometer
  • accuracy
    about 0.005
  • Long radii (gt 2 m) lower accuracy, error in the
    order of
  • 0.1 1.0
  • Irregulairty
  • The height departure from the ideal surface
    figure
  • ¼ power specification (Rule of thumb)

7
Surface figureaspheric figure
  • Rotationally symmetric surface or off-axis
    section of the surface that has rotational
    symmetry
  • General asphere with spherical, even and odd
    polynomial terms
  • Toroid
  • Concave or convex cylinders and axicons (almost
    impossible with conventional process)
  • Fresnel lens, or grating type surface
  • Surface defined by splines or differential
    equation
  • Surface slope
  • 2 arc sec or 10 microinches/ inch

8
Surface figure test
  • Talysurf contacting profilometer
  • Scan the part
  • Measure the departure of the surface from
    theoretical shape
  • Interferometer
  • Overall performance
  • Null test

9
Surface finish
  • A periodic residual grooves from the tool
  • Groove height depends on the feed rate the
    radius of the cutting tool
  • Groove height 10nm
  • Grooves scatter and diffract light
  • Limits the application of SPDT technique in
    infrared
  • Dont use scratch/dig specification

Surface roughness 40 Å rms
10
Post finish
  • SPDT usually provide adequate surface figure
    accuracy
  • Post finish can smooth out the residual grooves
    and minimize the scatter for the application of
    shorter wavelength
  • Avoid post finish it may change the surface
    figure

11
Advantages of SPDT
  • Easy to program
  • Setup can be changed quickly for short runs of
    optics
  • High degree of precisions in mechanics
  • Permits variations on surface shape, aspheric,
    toroidal, diffractive optics
  • Fast directly turn the surface to its finished
    tolerances
  • Cost effective

12
Limitation of SPDT
  • Produce only one optic at a time
  • The size of the work piece is limited by the size
    of the SPDT machine
  • Mostly applied to infrared optics

13
Example
14
Reference
  • 1. The Handbook of Optical Engineering
  • 2. Robert A. Clark, Design and Specification of
    Diamond Turned Optics
  • 3. Hillary G. Sillitto, Analysis, tolerancing and
    diagnosis of diamond maching errors
  • 4. Mark Craig Gerchman, Specifications and
    manufacturing considerations of diamond machined
    optical components
  • 5. E.R. Freniere and J. Zimmerman, Specifications
    for diamond-turned surfaces
  • 6. Paul R. Yoder, Opto-Mechanical System Design
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