Mechanical Construction

Design Parameters

This microscope is designed to be built by students in a few lab periods. In most places, the trade-off between resolution and cost has been tilted toward the cost side. The priority list, from highest to lowest, is:

Build time of about six hours.
Setup, troubleshooting, and testing in three hours.
Cheap components.
Modest tooling requirements.
Resolution in the nanometer range.

Part List

One ¾ slide repair coupling – Home Depot part number: 032888605046

Two ½” plug MPT - Home Depot part number: 049081143145

One small magnet (8mm x 3mm) - Home Depot part number: 095421070459

One piece of circuit board material (0.037”, FR4, Single, 1oz) – Ebay

One spool of 30 gauge magnet wire or ribbon cable - Ebay

One 27 mm Piezo Transducer Sound Disc (20mm PZT) - Ebay

One phenolic standoff 3/4” long by 1/4” diameter - Ebay

One DIP socket (any size) - Ebay

One 1¼ to 1½ reducer bushing - Home Depot part number: 034481062271

One NEMA 17 stepper motor - Sparkfun part number: ROB-09238

One brass 2mm to 5 mm motor coupler - Ebay

2-56 threaded rod - Ebay

One 7” Hose Clamp - Home Depot part number: 078575179957

Tooling List

Hand drill or drill press.

3/4” drill bit.

Vise or drill press clamp.

2-56 drill and tap set.

Hot glue gun.

Soldering gun and solder.

Scissors, side cutters, etc.

Hacksaw or bandsaw.

Razor blade.

Multimeter.

1. Housing Preparation.

1. Disassemble the ¾ Slide Repair Coupling into its three component pieces (cap, slider and housing).
  1. - Try to leave as much grease on the orings and sliding surface as possible since it will be required for normal operation.
    - Clean the grease off any surface that you will be gluing to.
2. Using the drill or drill press and the 3/4” bit, cut the sample access hole just below the threads of the housing.
  1. - During drilling, use safety glasses, a vise, and observe all safety precautions.
    - In the picture, the hole was drilled a little too close to the flange and cut into it. This configuration still works, but it looks messy.
    - The edges of the hole should be smooth so the orings do not catch on them.

PVC slider with access hole machined into side.

2. Slider.

1. Prepare the plugs.
  1. Cut a rectangle of thin circuit board just smaller than the plug’s outer diameter and hot glue a magnet to the center of the non-copper side.
  2. Solder a six inch length of wire to the circuit board.
  3. Hot glue the circuit board to the plug as shown on the left side of the picture.
  4. Drill and tap a 2-56 hole in the exact center of the other plug as shown on the right side of the picture.
  5. (Optional) Use a saw and cut the hex flange down to ½ its height.
2. Prepare the slider.
  1. Cut the non-o-ring end off the slider so it is 50 mm long and smooth the edges of the cut.
  2. Press the plugs into each end of the slider.
    - The plug with the foil and magnet goes into the end nearest the o-rings.
    - The plugs should fit tightly so they will not need to be glued into position.

Top plug on left and bottom plug on right.

3. Piezo and Cap.

1. Use a ruler and razor blade to cut the silver material on the piezo disk into four equal quadrants. The white layer on the piezo disk does not need to be cut. Verify electrical decoupling using an ohmmeter.
2. Solder on five small wires – one to each quadrant and one to the yellow base.
  1. Use magnet wire with each piece about six inches long.
  2. Try to use as small amount of solder and contact time as possible.
  3. All five wires should be connected to the same side.
3. Use hot glue the phenolic standoff to the center of the yellow side of the disk.
4. Attach a tip holder to the end of the standoff.
  1. The tip holder should be made from one section of a DIP socket.
  2. Solder a six inch section of magnet wire to the end of the DIP socket.
5. Hot glue the piezo to the cap.
  1. A small hollow in the cap may need to be cut to allow the piezo to sit flat on the cap.
  2. The five wires from the piezo should feed up through the hole at the top of the cap.

Top cap with piezo mounted with top view on left and bottom view on right.

4. Prepare the Motor.

Stepper motor with coupling to threaded rod.

1. Use a 2-56 tap to cut threads in the 2mm end of the motor coupler.
2. Cut a 25 mm long length of 2-56 threaded rod and thread it into the motor coupler.
3. Tighten the setscrews in the coupler to attach it to the motor and the threaded rod.

5. Assemble the STM.

1. Push the slider fully into the housing and feed the wire through the hole you drilled in the housing.
2. Screw the end cap unto the housing and feed the tip wire through the hole.
3. Push the gray reducer bushing onto the housing.
4. Manually thread the motor assembly into slider until the housing until the motor touches the bushing.
5. Place the hose clamp around the STM and tighten it to hold the motor to the slider. Except for the green wire and the black connectors on the magnet wire, the assembly should look like the picture below.
  1. - The clamp will need to be positioned so that the access hole and the motor wires are not blocked by the clamp.
    - Rotate the gray reducer bushing so that the bumps on it do not hit the hose clamp.

All STM parts in place and held together with a hose clamp.