Introduction: A Working, Old-Timey Stirling Engine - Hand Tools Only!
The text of these instructions are also available on Google Drive at https://docs.google.com/file/d/0B_yXLsNjezyeXzVmSGc0QVZ6LVE/edit?usp=sharing
Below is a very brief introductory video. A more detailed overview of this engine is available here
This model is based on a design by Darryl Boyd (http://boydhouse.com/stirling/) with a few changes inspired by Junkie (http://sites.google.com/site/reukpower/can-stirling/stirling-generator-2) as well as several others.
You'll need the following:
Tools:
Electric drill and metal bit set
Screw drivers
Vise grips
Socket wrench set
Hack saw
Pipe cutter
Sandpaper
Awl (or long nail)
Hammer
Rat-tail file
Scissors
Metal snippers
Carpenter's square
Pliers
Wire cutting pliers
Boxcutter knife
Clamps
Table saw or hand saw
Jig saw
Can opener from Boy Scout or Swiss army knife
Materials:
For the Frame
-3/4 plywood (a 2ft x 2ft piece)
-2 pipe straps (for 1in pipe)
-about a dozen 1-1/2in drywall screws (or similar)
-oak or hard pine strip (1/4in x 3/4in x 2ft)
For the Displacer cylinder
-1 or 2 empty aerosol can 2.5in diameter x 8in tall (hairspray, bug spray, spray paint, etc)
-4 or 5 12oz soda cans
-2 coffee cans
-old bicycle wheel- from at least 26in bike (ask local bike repair shop)
-Steel wool - medium
-Terminal blocks (regular and mini - from Radioshack)
-High temperature RTV silicone gasket maker (from auto parts store)
For the Power cylinder
-3/4in copper pipe (1 or 2ft piece from hardware store or ask plumber)
-Repair pipe for 3/4 pipe - comes in 2ft pieces
-3/4x1/2 Female adapter
-1/2x1/8 Pipe bushing (1/8FIPx 1/2MIP)
-3/8in Threaded lamp repair pipe (plus hex nuts)
-1/4in T-nut (Aluminum binding post w/ screw)
-5in clothesline pulley
-long rubber bands (about 5in dia. to fit pulley)
-JB Weld high temp epoxy (from auto parts store)
-Valve grinding compound- water based (from auto parts store)
Other hardware
for connecting rods:
-3 or 4 clothes hangers (in good shape - not bent up)
for pulley axle:
- #8x 2-1/2in bolt with nut and 4 washers
- 2 nylon T-flanges
- Threaded #8 aluminum spacers - one 1/4in, one 3/4in
for pulley arm:
- #6x 1-1/2in bolt two 2 nuts and 4 washers
- Threaded #6 aluminum spacers - three 1/4in
For beam:
-#8x 2-1/2in bolt with nut and 4 washers
- 2 nylon T-flanges
- 1/2in T-nut (aluminum binding posts)
- 1 washer to fit over T-nut
- Threaded #8 aluminum spacers - one 3/4in
- #8x 1in bolt and nut
- 4 fender washers to fit
For generator:
-small DC electric motor
-small plastic pulley or screen door roller (screen patio door repair parts)
-tubing that tightly fits the motor's axle to act as a bushing
-nylon spacer that will receive the axle bushing AND fit the small pulley
-extra large rubber band (about 4-1/2in diameter)
Step 1: Build the Frame
NOTE: The frame made in STEP 1 was made after I built this engine, so the frame you see here will look different than in later steps. The measurements are all the same, however. I thought I should show a more straightforward way of making the frame than I did before. The main difference is the placement of the 3 x 4.25in power cylinder mount.
Cut out plywood and mark as shown (Photo1). If you don't have a table saw, try to find a 2x2 piece with straight (factory cut) edges at a hardware store or cabinet shop, and then cut out your pieces with a hand saw, being sure to use the factory edges for any edges that will be screwed together. This will help keep your frame rigid.
Screw the pieces together thru the bottom of the 8x12 base (2). It's really not important that the pieces be straight on the line as shown, but the front edges do need to be flush or lined up together.
Center the long edge of the 4x12 back brace on the 2in mark (3). Screw thru the face of the 6x9 main engine mount, then up thru the bottom of the base as well.
Screw the 2x9 beam support to the brace, lining up the beam support's centerline with the 2in line on the engine mount.
Line up the centerline on the 3x4.25 power cylinder mount with the horizontal and vertical lines on the engine mount (5). You may want to put a small block on the backside, too, in case the screws stick out in the back.
Attach two pipe straps to the power cylinder mount so they are centered over the centerline (6).
Drill two holes to fit a #8 T-flange at the distances shown (6):
13-1/2in up from the base and on centerline of the beam support;
6-1/4in over from that same centerline on the main engine mount
TIP: To help get these holes more perpendicular without a drill press, place a 1-1/2in block with a square edge next to your drill bit and use the edge as a guide to keep the drill at 90 degrees from the piece being drilled (7).
Finally, If you wish to mount a motor as a generator later, center a hole for your motor at 3-1/4in from the center of the hole you just drilled on the main engine mount.
Step 2: Add Wheel and Beam to Frame
Adding Wheel and Beam to Frame
Clothesline pulley frame (1) must be removed by placing axle pin with it's head down over a hole in a piece of wood and striking the backside or hammered end of the pin with a nail set (2). This should push the pin through the frame so the wheel falls out.
Then add the 3/4in #8 aluminum spacer as shown (3). If the spacer doesn't protrude just a little (1/32in or so) you can file or sand the hub down a bit. With washers on either side of the spacer, tighten the washers with a 1/2in spacer and check that the wheel spins freely.
Remove the hub bolt and drill a hole for the #6 1-1/2in bolt that serves as the pulley arm (5&6). On the front side of the pulley, add #6 1/4in spacer, a nut, washer, 1/4in spacer as shown (7&9). Make sure these are tight.
Place a T-flange on either side of the hole in the frame for the pulley assembly, replace the axle bolt thru the hub then add washer, 1/2in spacer and another washer on bolt then push it thru the flanges (8) and fasten with a washer and nut on other side.
Cut the oak strip for the beam at about 14-1/2in, find the center and drill for the bolt. Then at 6.25in from the center, drill a hole for the aluminum binding post to connect with the pulley arm later.
Drill a hole in the upright strip on the frame to receive the T-flanges for the beam axle at 6.25in over from the pulley hub, and 13-1/2in up from the base.
Using a #8x 2-1/2in bolt for the beam axle, put a washer on the bolt and push thru the center hole on the beam. On the back side, add a washer, 3/4in spacer and washer (10) then add the T-flanges to the upright on the frame, push the bolt thru the flanges and fasten tight with washer and nut (11).
Beam should swing freely - if not make sure the 3/4in spacer isn't too tight against the beam. You can loosen it up just a little against the beam, and then when you tighten the nut on the other side, that will lock the spacer against the T-flange. Use a driver to hold the bolt while you tighten the nut.
Step 3: The Displacer Cylinder
The Displacer cylinder is made from an aerosol can that is 2.5in in diameter and 8in tall. First make sure the can is emptied of all pressure by turning the can upside down and pressing spray button (2) until no hiss can be heard.
Place an awl or nail in the groove along the can rim and - covering the top around the awl with a rag just in case - punch the tip of the awl through the can with a hammer (3&4).
Use a can opener to remove the top (5 - 7), and carefully clean out the can. Hair or bug spray cans are easier to clean with soap and water, but paint cans are probably more common. Mineral spirits will do the job for paint.
A rat-tail file or curved rasp will smooth the inside of the can rim (8). Mark the midpoint of the can's seam to drill the port for the power cylinder (9). The seam of the can is the stiffest part of its wall and will best hold the nut for the cylinder fitting.
Clamp a piece of wood to the worktable so that about 10-12in extends out from the table's edge (9). A 3/4in piece clamped on its narrow edge, a large dowel or other piece shaved round will work.
Place the can on the wood as shown (9 - this will keep the can from denting when you drill) and drill a small pilot hole at the seam midpoint. Then drill a 3/8in hole while pressing the can onto the wood.
Screw the threaded lamp pipe into the bushing and add a hex nut (10), then tighten with pliers or a flat driver jammed into the center.
Clamp the bushing down and use a hacksaw to cut the threaded pipe flush with the outer face of the nut (11). Carefully roll the nut back and forth over the cut edge of the pipe and file off any small burr before completely removing the nut (12). This will clear out the pipe threads and ensure that you can put the nut back on later.
With the nut removed, screw the pipe thru the port on the spray can's seam (13).
Place a small piece of rolled up tape with sticky side out into a 9/16in socket wrench and stick in a large nut that will leave enough room at the end for the small nut from the threaded lamp pipe to fit (14) . Use another piece of tape to secure this small nut.
Using the socket wrench to hold the nut, screw the bushing/pipe from outside the spray can and tighten. Hard. Set your unfinished displacer cylinder aside for the moment.
Step 4: Power Cylinder and Piston
The Power Cylinder is made from copper repair pipe for 3/4in pipe. The Power Piston is cut from 3/4in copper pipe. When picking out a piece of repair pipe, try to find one that is undented and slides easily over a section of 3/4in pipe. Both types of pipe may come in 2ft sections - if not try to find a nice plumber to give/sell you some scraps.
The female adapter (2) fits 3/4in pipe to a certain depth limited by the ridge on the inside of the non-threaded end of the adapter. You can see it in photo 4. This end needs to be cut down a bit (3) to maximize the distance available for the piston to move thru the power cylinder. Cut the adapter so that the depth from the unthreaded end to this inner ridge is 3/8in.
Use a penknife (6) or rat-tail file (8) to remove the burr on the inside of the cut edge of the adapter.
Cut a 3/4in long section of the 3/4in copper pipe and fit it inside the adapter (4). This will allow the repair pipe to be coupled with the adapter later.
Cut a 3.5in section of repair pipe for your power cylinder (5). You will need to cut the burr from the inside of both ends of this piece (6). One end needs to slip onto the adapter coupling, and the other must be VERY smooth to receive the power piston.
To smooth the inside of this piece dip the end of a longer piece of 3/4in pipe into valve grinding compound (7) and spend several minutes grinding these two pieces together back and forth and round and round, until they slide easily. This can be pretty messy, so wear rubber gloves if you can get a rag or paper towels and do this step outside. Wash everything with plenty of soap and water, using a toothbrush to scrub the insides of the pieces of pipe.
From the now smooth end of the 3/4 pipe you used to grind out the 3.5in cylinder cut another section of 3/4in pipe to serve as the piston. It should be 3/8 to 1/2in long. You dont need to cut the burrs off the inside.
Use fine sandpaper on a dowel to smooth the cylinder and piston some more. IF you can't use the grinding compound, use coarse, medium and fine sandpaper like crazy (8) on both pieces until everything slides well.
Now you have the main pieces of your power cylinder (9). Stick the piston piece down on a small square of duct tape (10) and set aside.
Now you need a piston rod, made from about 3in of coat hanger wire and bent as shown to fit around a T-nut (or binding post). To bend it well, I've found that a drill bit serves as a good mold (11). Clamp a piece of 1-1/2in wood to the table as shown and drill bit into end of the piece and remove the drill (12).
Set the vise grips to clamp the very tip of the wire to the bit shaft - when you look at the grips from above, the wire should point at an angle from the corner of the vise jaws (see photo 13). With your hand or pliers, bend the wire around the bit shaft a full 360 degrees(14 & 15), then release the grips.
The wire now has a nice pig-tail that has to be clipped (16) so that when squeezed into line (17) the loop will be completely closed. Place the loop back on the bit shaft (18) and pinch hard with the pliers to close the loop tight and make it as round as possible.
Use needle nosed pliers to bend the loop so that the center of the hole is in line (19) with the straight part of wire. Test the fit of your loop around the T-nut (20). The piece should also lie flat on the table - use pliers to adjust.
At 3/4in from the bottom of the loop, bend the wire to 90 degrees (22) and cut the excess off at 1/4in from the bend (23).
Step 5: Displacer Piston and Top
The top of the displacer cylinder will come from a soda can bottom. To find the center of the bottom of the can, try this trick I saw somewhere else on the web: first use two pliers to bend a nail until the tip looks to be close to half the diameter of the can bottom when the head of the nail against the ridge as shown (1) and scratch a small arc in the middle. Now move the nail head about a third of the way around the ridge and make another scratch to intersect the first, and then move another third and scratch again.
You should now see that all the intersecting lines indicate the center point. Mark it. Now we need to drill this hole to receive a spoke nipple from a bicycle wheel.
Unscrew a nipple from a wheel rim (3) and, select a bit that is slightly smaller than the nipple shaft (4), drill the can bottom. Even though the nipple is 5/32, I used a 9/64 bit, making a tighter fit for the nipple.
Remove the spoke, cut off the threaded end and find a bit to match spoke diameter (5). The spokes I used were between 3/32 and 5/64, so I went with the smaller bit. Holding the nipple with pliers, drill it out and then continue to run the drill thru to make the hole slightly larger so the spoke slides easily through the nipple, without wobbling around too much.
Laying a marker on some books or wood scraps so the tip is 1-1/2in to 2in above the table top(6), place can on its bottom, bring can wall up to the marker and turn can to mark around it. Flip can onto its top and do this again. Cut the can at this second mark with box knife and scissors (7). Then use scissors to cut up to the next mark (8) and cut as smoothly as you can around the mark, trimming any burrs. This bottom piece with the hole will be the top of your displacer cylinder. Put the drilled-out spoke nipple in the hole and set aside with power piston and other power cylinder pieces (9).
Find centers for TWO MORE soda can bottoms, BUT drill center hole to size of the spoke itself. Then cut the bottom out along the highest part of the ridge (10) to make a bowl or cap. Drill 4 or 5 more holes in the caps as shown (11).
Now to make the displacer piston:
The head of the spoke is bent 90 degrees to its shaft. To straighten this, we just run the spoke thru a hole in the hub so shaft points away from hub (12). With spoke head firmly in hole, tightly clamp edge of head with vise grips, letting spoke shaft run along vise handle. WIth pliers, grab spoke close to hub and bend the spoke straight up (13). Remove vise from hub and use with pliers to straighten the shaft (14).
Next you'll need some way of locking the piston components onto the spoke shaft. One solution is to cut down a mini terminal block. These come with several units encased in plastic (14) which needs to be cut off as shown in photos 15-18. Once the inner metal unit is free, Hold one end with vise grips and cut in half with a hacksaw (19) and reinsert the screws (20).
Squeeze the folds out of a whole pad of steel wool, so that it is fairly round. Place one soda can cap piece on the spoke (21), push the spoke thru the steel wool and add the second cap.
Push the top cap down to compact the wool to about 2-1/2in, then slip the cut down mini block against the cap (22) and lock it with screw driver and then pliers (23). Check that the final length between caps is 2-1/2in. Squeeze the wool with your hand so it doesn't extend too much beyond the edges of the caps.
This is a finished displacer piston - also called a regenerator.
Step 6: Assemble Cylinders and Mount on Frame
Now you have all the pieces that need to be glued together. First thing is to hold the piston rod in the pliers as shown with rubber bands (1). The bent bottom end of the rod should be suspended about 1/4in from the duct tape under the piston body.
Find some toothpicks, or wood or stiff plastic strips to help apply the epoxy (2&3). Use about a tablespoon from each tube, mix well.
Move the piston rod out of the way and ladle some glue into the piston nearly to the top(4). Then put the piston rod back into the glue, being sure to center the rod in the piston body (5). Wait until dry, then remove the tape.
Skim the inside of the adapter, push in the coupler, skim the inside of the ROUGHER end of the repair tube and push onto the adapter. Wipe off any excess on the outside. Photo #6 is a good example of how NOT to do it. Too much glue.
Push the displacer piston in the displacer cylinder (7&8), slip the rod thru the nipple and slowly press the can top onto the displacer cylinder (9). Apply a small amount of epoxy under the head of the spoke nipple - enough to seal under it without getting any on the spoke - and be sure the nipple is pushed down completely into its opening. Wait until dry.
Once the epoxy has dried, mark the displacer piston rod and get it ready to attach later. Pull the rod all the way up and then, looking thru the bushing, push the rod down until you see the bottom cap of the piston (10). Mark the rod at the nipple on top of the cylinder.
Then continue to push the rod down until you see the top cap and mark the rod again (11).
Measure the distance between the two marks (12). This midpoint will be used when connecting the rod to the beam later.
Screw the power cylinder onto the bushing on the displacer cylinder and slide the power cylinder thru the pipe straps on the frame (13). NOTE: On the frame made as in STEP 1, the end of the power cylinder is to be flush with the edge of its mounting block and will be 6-1/4in from the center of the pulley hub (14&15).
If you haven't already done so, screw in the top of the pipe strap to secure the power cylinder.
Step 7: Connect Piston and Beam to Pulley
Place power piston in the power cylinder flush with the end of the cylinder (1).
Brace the pulley with a rubber band so that the piston rod arm is at its farthest distance from the end of the power cylinder (1).
Now we need to make an extension rod connecting the piston rod with the pulley arm. As in Step 4 with the piston rod, but using at least a 10in piece of coat hanger, make a loop to fit the short T-nut. Then join this loop with the piston rod loop using a 1/4 T-nut, and lay the other end of the rod on the pulley arm (1). Mark the point on the wire where it touches the piston rod arm on the pulley.
Take the piston out of the cylinder, unscrew the T-nut and disconnect the extension rod from the piston. Add two inches from the mark just made on the extension rod (2), cut the wire and make another loop at the other end, trying to keep this loop in the same plane as the first so that they both lie flat on the table.
At 4in from one loop make a bend as shown (2) using two pliers and being sure to keep the bend in the same plane as the loops so the rod lies flat.
About 1/2in or so from this bend, make another (2&3). This bend will you change the length of the rod, first when connecting the piston rod to the pulley arm, and then later when making small adjustments to get the engine running.
Use pliers to adjust the piece as needed so that the wire lies flat on the table (3).
Hold the extension rod up to the piston rod to see how much to adjust these bends to lengthen or shorten the rod so it reaches the pulley arm. Recheck to make sure the extension lies flat on the table. It's OK if the arm is a little long - the piston will just ride deeper inside the cylinder - but if it's a little short, the piston will come out beyond the edge of the cylinder during its cycle.
Reconnect the piston rod to the extension with the T-nut (4), oil the piston (5) and place it back in the cylinder and attach other end to the pulley arm as shown (6&7). When you turn the pulley, the piston should slide easily and its outer edge should always stay inside the cylinder.
Cut two more pieces of coat hanger wire, each at least 7in long. In one piece, make a loop to fit the T-nut on the beam, then attach and let hang. In the other piece make loop in one end to fit the spacer on the pulley arm.
Slide a large terminal block over the hanging piece and then slide in the straight end of the piece that fits the pulley arm (8).
With the pulley arm locked with the rubber band as shown (9), attach the lower loop to the pulley arm (10). While holding the beam level, tighten the block screws.
Remove the excess or overlapped wire seen in photo 8, by marking the excess about 1/8in from the terminal block, then loosen the block and let it slide down to the pulley. Cut at the two marks then reassemble and tighten the screws with screwdriver and then harder with pliers. The piston extension rod should be on the inside of the pulley arm and the pulley-beam rod on the outside (10).
Step 8: Connect Displacer Piston
Now we'll connect the displacer rod to the beam (1).
Make a loop out of about 4in of coat hanger (2) then trim the shaft to about an inch.
Make a hook out of another 4in piece of coat hanger wire (2) so that the loop you just made will hang freely in the hook.
Pull down the beam and pull up the displacer rod (3), hold it over the beam and mark the beam where the rod crosses the beam's midline. Drill a hole thru the beam at this mark - hole should be just large enough so coat hanger wire will turn freely.
Put a large terminal block on the shaft of the looped piece you just made (4), making sure the shaft only extends halfway into the block and then lock the piece with one set screw. Now attach the block to the displacer rod using the other set screw.
Brace the pulley with a rubber band as before so that the pulley arm is at 3 o'clock and the beam is level. Put the hook through the loop and pull the displacer rod up until the midpoint mark you made earlier shows just above the spoke nipple. the hole you just drilled in the beam, and mark where the hook's shaft meets this hole (5). Bend the hook 90 degrees at this mark, making sure the hook lies flat when done (6).
Put the hook back thru the loop, push the shaft thru the hole (7) and lock from behind the beam with a mini terminal block (8).
The following steps will help make sure your engine starts the first time:
1. Check the balance and smoothness of the beam by detaching the piston from the pulley, reattaching the beam-pulley connector and then spinning the pulley to see if the arm will stop at any point, or if it tends to go to the bottom. You may need to add another bolt to the beam (9) and put enough washers on it - fastened with a nut - until the beam seems to move with complete freedom - 2 or 3 complete revolutions when you give the pulley arm a good spin. Counterclockwise.
2. The steel wool of the displacer piston may hang a little on the nut holding the power cylinder on, but this should clear up after a while.
3. Make sure the loops are not too tight on the piston arm and at the T-nut holding the piston rod and extension together. Use a little oil on these places and where the displacer rod runs thru the spoke nipple.
Step 9: Cooling Chamber for Displacer Cylinder
If you have an extra aerosol can the same size as your displacer cylinder, use that can for this step. Otherwise,
Disconnect the displacer rod from the terminal block, loosen the pipe straps holding the power cylinder and slide the assembly off the frame. Unscrew the power cylinder from the displacer cylinder.
Place the displacer cylinder onto the bottom of a coffee can - or some other can with a wider diameter - center it and mark around the base of the cylinder(1).
Drill a 1/4 hole in the center of the coffee can (2) and from this hole use metal snippers to cut out to the first ring (about 1/2in in from the mark (3).
Snipping out from the cut edge, make several small cuts to the mark (4 & 5) and bend the tabs down (5). Turn the coffee can upright now and press it over another soda can or spray can so it slides down without too much pressure(6).
Shorten the coffee can, cutting down from the top to the second crease (7&8). Use pliers to bend this sharp, cut edge over to prevent cutting yourself (8).
Slide the coffee can down over the displacer cylinder (10&11) to about 1/2in from top of the cylinder (should also be about 1/2in from the power cylinder fitting).
Use the silicone gasket-maker to seal the bottom (12&13). Apply a generous bead and smooth lightly with your finger. The silicone washes off skin easily with soap and water.
Slide the power cylinder onto the frame, tighten the pipe straps. The distance from the center of the displacer cylinder to the pulley hub should be 12-1/2in. Reconnect the displacer rod to the beam, reinsert the piston and reconnect the piston rod to the pulley arm.
Cut a second coffee can in half and fit it just as before to go around the bottom of the displacer (14)- upside down of course. No need to seal this can with the silicone.
Once the silicone gasket dries, pour in a little water and check for any leaks.
And that's it! - you're ready to fill up the cooling chamber with ice water and try to get it going over a heat source. Remember to do your first run in a well ventilated place - the displacer cylinder linings and paint will burn off and can get a bit smelly and smokey. This will ease off after a couple of heatings.
Step 10: Troubleshooting and Adding a Generator
Troubleshooting:
1. Check the balance and smoothness of the beam by detaching the piston rod from the pulley arm, reattaching the beam-pulley connector and then spinning the pulley to see if the arm will stop at any point, or if it tends to go to the bottom. You may need to add another bolt to the beam (Step 8, photo 9) and put enough washers on it - fastened with a nut - until the beam seems to move with complete freedom - 2 or 3 complete revolutions when you give the pulley arm a good spin. Counterclockwise.
2. The steel wool of the displacer piston may hang a little on the nut holding the power cylinder on, but this should clear up after a while.
3. Make sure the loops are not too tight on the piston arm and at the T-nut holding the piston rod and extension together. Use a little oil on these places and where the displacer rod runs thru the spoke nipple.
4. May have to regrind the power cylinder.
To add a generator, I've found that some mechanical pencils have a plastic tube that will fit a small electric motor's axle. This tube will almost fit into a nylon spacer (may have to drill out the spacer a bit) which in turn will fit a small roller found in hardware stores, either in the same aisle as the spacers or packaged as a replacement roller for screen doors (1&2). If you can't find a pencil tube, some hobby shops have small brass or steel tubing that might work inside the nylon spacer. I'm sure you'll think of something-just try to keep the pulley from wobbling.
These fit tightly enough and will work with an extra large (4-1/2in dia.) rubber band as a belt (3).
