PINHOLE INVESTIGATIONS 

Making a Round Tabletop Light Source

©1998 Exploratorium

Equipment

  • Table saw, to cut long length Burke tube into 9" lengths
  • Band saw to cut wood disks
  • Small, circular hand-held saw, 3-3/8 (Makita 5090 D or comparable) to cut four windows in the tube
  • Drill, with 7/16" bit (for cord hole), 1/8" bit (for pilot holes) and 1" bit (for vent holes in disk). (Drill press makes preparation of disk much easier.)
  • Screwdrivers - Phillips head and regular in small and medium sizes
  • Wire cutter/stripper

 

Consumable Supplies for one Round Light Source

  • 1 sheet sandpaper (medium grade)
  • 1 Tube - Burke or Sono Tube, used for concrete construction, 10" diameter - preferably unwaxed, cut to 9" lengths. Sometimes sold only in 10-ft. lengths. Approximately $2/ft.
  • 1 sheet of Plywood (12" x 12" x 3/4") for circular disk. Try to get scraps.
  • 1 Electrical cord - 8-ft., heavy-duty cord with switch and plug attached
  • 4 #6 pan head sheetmetal screws (3/4") (disk to tube)
  • 2 #6 pan head sheetmetal screw (1/2") (porcelain, disk bracket)
  • 1 6/32 bolt and hex nut (1/2")(wall bracket)
  • 1 Standard porcelain lamp fixture
  • 1 Plastic cord fastener ("p-straps")

 

Making the Round Light Source

  1. If you are making more than one Round Light Source, tubes can be cut into 9" lengths using a table saw with a 9" jig.
  2. Use a small (5/8") circular, hand-held saw to cut four windows (4" x 2" 1/4") in the tube.
  3. Cut disk from plywood on a band-saw to fit inside of tube, snug, but not too tight. Drill five 1" vent holes in disk.
  4. Drill four 1/8" holes (A) in tube and disk together, at the end of the tube that is opposite from the "windows." Holes should be approximately equally spaced around the circumference of the tube.
  5. Drill one 7/16" hole (B) for cord in the side of the tube.
  6. Drill one 1/8" hole (C) for P-strap to support cord inside of tube.
  7. Drill eight 1/8" holes (D) for brass fasteners to hold masks.
  8. Sand disk and tube.
  9. Attach the tube to the disk with the 3/4" #6 panhead sheetmetal screws.
  10. Push cord through (B) large 7/16" pre-drilled hole in tube. This must be done BEFORE attaching porcelain fixture.
  11. Attach brackets to the wall of the tube (with the 1/2" 6/32 bolt and hexnut) and to the disk (with the 1/2" #6 panhead sheetmetal screw).
  12. Unscrew top of porcelain fixture. Trace outline of fixture, including holes for screws on center of disk, and drill two pilot holes for screws for fixture.
  13. Attach porcelain fixture to the center of the disk, using 1/2" #6 panhead sheetmetal screws.
  14. Attach black and white wires to porcelain fixture. Third wire is not necessary and can be cut since no part of the Round Light Source is metal, so it does not have to be grounded. Prepare the wires by twisting them so that they are tightly bound. Attach the black wire to the brass screw and the white wire to the gray screw. Bend them in a U-shape, and attach to the screws as illustrated: