Model Steam Engine

Working model of a stationary steam engine
  • This is the finished model. The curved tube is the steam input pipe from the boiler. The exhaust steam is vented through the vertical stack on the horizontal manifold. The manifold collects exhaust from the two exit ports. Other details are shown in the following slide show.
  • Here the cylinder is machined out of a solid cast iron rod 2-1/2" long and 1-1/2" diameter. A boring bar is used to enlarge the hole that was previously drilled. The piece is off-set to provide more material on one side to accommodate future valve ports and the steam channels.
  • Deep cuts heat the cutting lube to smoking hot.
  • The bore diameter is checked with a steel rule. It looks like it has about .015" to go to be the designed 1" bore. (I had not yet acquired a digital micrometer.)
  • Making the Crankshaft One of the crankshaft throw cheeks being tapered. The dowels are 5/16", the same as the crankshaft journals. The 3/16" lathe cutting bit indexes the piece so all tapers are easily made the same.
  • One of the crankshaft throw cheeks being rounded at one end. Repeated cuts made after rotating the piece a little at a time makes a mostly-rounded end that can be finished on the belt grinder.
  • Here the cheek piece is turned back a little to provide a clearance boss for the connecting rod "big end".
  • This tool was made to clean up the crankshaft rod journal after silver soldering the 5/16" rods to the cheek pieces. The semi-circular hole was lined with carborundum paper and squeezed around the journal while the crank was slowly turned in the lathe.
  • This is what the finished crank looks like. The connecting rod journal and the long rod, which will be cut to length later, were silver soldered to the cheek pieces. A disk grinder was used to part the long steel rod between the cheek pieces after the soldering operation. This assured that the the crank would be straight.
  • The crank is checked for "run out". Three thousandths of an inch at this distance is close enough for an engine made at the turn of the last century.
  • About the connecting rod.
  • Here the compound rest of the lathe is set to turn a 2 degree taper from the center to the ends of the connecting rod. The far end is supported in a cone shaped receiver The end of the rod had been turned to the same cone angle. The ends of the rod are still be be threaded to 10-32 on the lathe to within about 80 percent depth to assure a more accurate thread when finished with a regular thread cutting die.
  • This is one side of the connecting rod "big end" being milled with a 1/2" end mill to form the radius to the extension pad. This extension will be drilled and tapped for the connecting rod. The connecting-rod end has been split, silver soldered together again, and then drilled for the rod bearing. After the end-cap bolt holes are drilled and tapped, the solder will be melted to separate the halves. The toothed bar and the lathe cutting tool help support the precariously held piece. The dime show the scale
  • This will be the brass rod bearing insert. There are two rectangles of brass soldered together and soldered to the brass piece in the lathe chuck. The soldered parting line and the center drill hole can be seen. Again the same dime.
  • The brass rectangles have been turned down to be a tight fit in the bore of the connecting rod big end.
  • The bearing insert set is drilled out with the first of s series of larger and larger bits. The small hose clamp is to assure the the soldered halves stay together.
  • The bearing inserts being finished close to the final size to fit the crankshaft journal. When finished the solder will be melted and the halves separated and installed tin the connecting rod.
  • The Crosshead The upper rail legs of the crosshead being detailed with a radius cut using a ball-end mill. The near rail is still to be detailed. The bottom legs are covered with trash and cannot be seen. The mill bit is 1/4" in diameter. The crosshead was milled from a solid 1-1/4" x 1-1/4" x 3" iron bar.
  • About making the "eccentric strap".
  • The eccentric strap roughed out is shown here lying on a shop drawing. Visible is the parting line where the two pieces are temporarily silver soldered together for machining. After machining, and after the bolt holes are drilled and threaded, the halves will be melted apart. There is a square-bottomed groove in the inside circumference of the strap that mates with a square-topped ridge on the eccentric disk. This keeps the strap in place on the disk.
  • The eccentric strap is being finished and detailed on a three inch lathe chuck. The slot for the connecting link is visible on the back side of the extension lobe. The dime shows the scale.
  • The eccentric strap machined and finished but waiting for the bolt holes to be be drilled and threaded before the silver soldered halves are parted. The orientation pips are visible. The roughed out valve operating rod is temporarily attached.
  • Here is a photo of most of the parts for the model steam engine. The rectangular object at the left is a 6" steel rule for size comparison.
  • A flyball govenner has been made and installed but not yet linked to a throttle valve. Click here to see pictures about how the flywheel was cast.