3. Cut the aluminum hot
and cold plates.
File or sand down the edge of the wire rod to make
sure it’s not causing any binding. If it still doesn’t fit,
try wiggling the plate around a bit to widen the hole.
Draw two 5" circles on your aluminum stock.
These are the top and bottom plates (cold and hot,
respectively) that power your engine. Use a hacksaw
or band saw, take it slow, and cut out the circles
(Figures D and E). They don’t have to be perfect; just
make sure they cover the displacer ring completely.
5. Build the top plate standoff.
Once the rod runs smoothly, cut a 1" piece of pipe,
C-stock, or angle stock (I’ve used both angle stock
and pipe for this), and cut a small square (or circle,
if you’re using pipe) of metal from the scraps you
cut while making your plates. Drill a hole in the exact
center of the small square (or circle). This will act as
a standoff to keep the displacer rod perpendicular
Here’s where problems can arise — not critical ones, to the plates.
but extremely annoying ones. Using your small drill Center the piece of angle stock (or pipe) over the
bit (the one that matches the diameter rod you’re hole and glue it down to the top plate with epoxy
using, in my case 5"), drill through the exact center (Figure G). Poke the wire rod through the holes in the
of 1 plate (Figure F). This will be your top/cold plate. plate and the standoff, making sure it slides smoothly,
Test-fit the rod in the hole and make sure it’s a and glue the standoff to the angle piece. As the epoxy
smooth fit. In order to maintain thermal efficiency, cures, check periodically that the rod still moves freely
we need this passage to be as airtight as possible, in the hole, and adjust if necessary. If the rod “freezes,”
but still allow the rod to run smoothly in and out of redrill the top hole with the next-larger bit.
the plate. If you wiggle the wire around, you may Finally, near the edge of the top plate drill a
notice that it tends to stick at any angle. Keep it ½"–¾" hole (Figure H). Bigger is better, but just
perpendicular to the plates. make sure the pipe you’re using for the piston
If the rod isn’t running smoothly, try this: Run the cylinder is slightly bigger than this hole (the pipe
bit through the hole again to make sure it’s clear. should not fit inside this hole).
Photography by Jim Shealy (A–C, G, H) and Ed Troxell (D–F)
4. Drill the top plate
to fit the rod.
70 Make: Volume 17