A Model Steam Engine as a Shop Project

  1. Cylinder - Cast Iron
  2. Piston - Cast Iron
  3. Rear Cylinder Head - Cast Iron
  4. Valve Plate - Cast Iron
  5. Steam Plate - Cast Iron
  6. Front Cylinder Head - Cast Iron
  7. Cross Head - Cast Iron
  8. Crank - Cast Iron
  9. Main Bearing - Cast Iron
  10. Eccentric - Cast Iron
  11. Fly Wheel - Cast Iron
  12. Main Shaft - Cold Rolled Steel
  13. Crank Pin - Cold Rolled Steel
  14. Connecting Rod - Brass or Cold Rolled Steel
  15. Cross Head Pin - Cold Rolled Steel
  16. Piston Rod - Cold Rolled Steel
  17. Valve Plate Stud - Cold Rolled Steel
  18. Valve Rod - Cold Rolled Steel
  19. Rocker Arm - Cold Rolled Steel
  20. Rocker Arm Pin - Cold Rolled Steel
  21. Rocker Arm Standard - Cold Rolled Steel
  22. Eccentric Rod - Cold Rolled Steel
  23. Spacing Collar - Brass or Cold Rolled Steel
  24. Eccentric Strap - Brass
  25. Connecting Rod Brasses - Brass
  26. Connecting Rod Bushing - Brass
  27. Rod Ends - Cold Rolled Steel or Brass
  28. Rod Ends - Cold Rolled Steel or Brass
  29. Rod Ends - Cold Rolled Steel or Brass
  30. Rod End Pins - Cold Rolled Steel
  31. Cross Head Guides - Cold Rolled Steel
  32. Cross Head Guide Blocks - Cold Rolled Steel
  33. Cross Head Slide - Cold Rolled Steel
  34. Base - Oak Wood


  • The steam engine described below was designed and built for two reasons: First, it was used as a class project in a school located near the main shops of one of our large railroad systems. Ninety per cent of the graduates will find their way into these shops. Obviously, the more these boys know about steam engines the more rapid will be their advancement. Second, the building of the engine afforded a wide variety of work and an opportunity of proving that 'Necessity is the mother of invention.'
  • Our shop equipment consisted of an eleven inch lathe and a twenty inch drill press; a power driven emery wheel and a bench with six vises. Other necessary equipments such as drills, reamers, files, chisels, etc., completed our list of tools. We had no shaper, no milling machine, no power hack saw (bandsaw), etc., so that opportunities for demonstrating the uses of the lathe and the necessity of doing lathe work on the drill press were very numerous.
  • The boys who worked on these engines were all in their second year. Their first year had been spent in carpentry, cabinet making, wood turning and mechanical drawing.
  • In machining the different parts of the engine no attempt was made to follow any rule for finishing one part after another as necessity required. In turn each boy was assigned a half day at the lathe, about every ten days. To illustrate, each of the ten boys in the class had a number. Thus, when No. 1 had had his half day at the lathe, No. 2 would follow and then No. 3 until each of the ten engine builders had had his half day. Then No. 1 would again have his turn. While the lathe and drill were busy the other boys worked at the bench.
  • Fig. 1 Equipment used by different students, p. 26
  • In the following paragraphs I shall not attempt to say which part or parts were finished first, but to explain how each part was finished, naming each operation in its proper sequence.

The Cylinder

  • The cylinder of the engine could have been bored on the lathe or on the drill press. The lathe was so small, however, that we decided to bore it on the drill press. This method was also more advisable, because a much better finish could be obtained, and an opportunity was given for the use of some tools which today are seldom thought of or used in the machine shops.
  • Fig. 3 illustrates how the cylinder was bored on the drill press. A boring bar was used for roughing out. A bushing was inserted in the drill press table to steady the bar while a cut was being taken through the cylinder. This first cut was slightly smaller than the finished dimensions.
    • Fig. 3 Cylinder Bored in Drill Press, p. 27
  • After the first cut was through we used a finishing reamer, or boring bar, as shown in Fig. 4. This type of boring bar is referred to above as a tool which is very rarely used at present. Blocks of wood fastened onto each side of the bar and turned to the dimensions required, prevent any vibration or chattering of the cutter and produces a very desirable mirror-like finish on the inside of the cylinder walls.
    • Fig. 4 Plug Used for Finishing Fly Wheel, p. 28
  • The next operation is to face the ends to the proper lengths. For this operation the cylinder is pressed on an arbor or mandrel and placed between the centers of the lathe. When pressing the arbor into the cylinder, it is well to spread a small amount of oil over the arbor to prevent any cutting or marring of the cylinder walls.
  • When the ends had been faced, the cylinder was clamped onto the face plate of the lathe, (Fig. 4 <strike>2</strike>), for the purpose of facing the valve slide side. Ordinarily this operation would be done on a shaper or milling machine, but our shop had none of this equipment so our lathe had to be used.
    • Fig. 4 Face Plate - Special Tools Used in Building the Engine, p. 27
  • The various holes in the ends and side were next drilled and tapped. The end holes were drilled by first laying out the cylinder heads, clamping them in place with a parallel clamp and drilling through each head with a 1/4“ drill. The heads were then removed and the holes in the cylinder drilled with a No. 12 or a 13/64” drill.
  • The next hold drilled was that in the valve slide side for the valve plate stud. This hole drilled with a 17/32“ drill and tapped out with a 5/8” tap. Extreme care must be taken when drilling this hole to avoid drilling through the cylinder wall. When this hole is drilled and tapped, screw the valve plate stud in place and assemble the valve plate and steam plate. Lay out the holes on each corner of the steam plate and drill through with a No. 18 drill. Remove the valve and steam plates and drill the holes in the cylinder 1/2“ deep with a No. 28 drill and tap with an 8/32” tap.
  • The drilling of the port holes was the very last thing done on the engine. The position of each hole was laid out on the steam plate and the entire engine with all working parts was assembled. The fly wheel was turned until the piston was at the extreme end of the forward stroke and then clamped in place. The inlet and exhaust ports for this stroke were then drilled through the steam plate and valve plate and for a short distance or approximately 1/8“ into the cylinder. After these holes were drilled, the fly wheel was unlocked and rotated in the opposite direction, or to the extreme end of the reverse stroke and the port holes for this drilled as described above.
  • The cylinder was then removed from the engine and placed on the jig as shown in the drawing, and the port holes drilled through. The inlet ports were drilled at an angle of 30 degrees and the exhaust ports were drilled straight. This was to allow any condensed steam which might enter the cylinder to escape easily. The inlet ports were drilled with a 5/16” drill and the exhaust ports with a 3/8“ drill.
  • The successive operations are:
    • (1) Rough bore to 2-7/32” diameter;
    • (2) finish bore to 2-1/4“ diameter;
    • (3) face the ends to the right length;
    • (4) face the valve slide side;
    • (5) drill and tap screw holes in the ends;
    • (6) drill and tap a hole for the valve plate stud;
    • (7) drill and tap holes for steam plate screws;
    • (8) drill port holes;
    • (9) scrape and finish the valve slide side

Steam Plate and Valve Plate

  • As will be seen in the assembly drawing, two plates were used in the valve mechanism. One was a movable plate, which we called the valve plate, and the other was the inlet and exhaust of the steam. The outer or stationary plate we called the steam plate. The valve plate was finished in the following manner. A 23/32” hole was laid out, drilled through the center of the plate and reamed with a 3/4“ reamer. Care must be taken to have the plate lie flat on the drill press table when reaming the hole.
  • An arbor was pressed into this hole and placed between the centers of the lathe. The sides were faced off to the proper thickness and the lathe work on this part was finished. The 1/4” hole in the arm was drilled and reamed, but the four valve holes were not drilled until the entire engine was assembled. The valve plate was ground with pulverized emery and oil after all other work had been done. By rocking the plate back and forth in the way that it was to run, a smooth flat face was obtained. If care is taken when facing the plate, time can be saved in grinding it.

Steam Plate

  • The steam plate was finished by grasping it between the jaws of the lathe chuck and facing off the inner side. The holes for the inlet and exhaust pipes were drilled and tapped out. The center hole was worked out to shape by first drilling two 5/16“ holes on 5/16” centers. The remaining metal was chipped out and the hole was filed to fit the valve plate stud. The stream plate was screwed into place on the cylinder and this was also ground to a true bearing surface with the valve plate.
  • The operations for the valve plate are as follows:
    • (1) Drill and ream a 3/4“ hole;
    • (2) face to the required thickness;
    • (3) drill and ream a 1/4” hole;
    • (4) grind to a bearing surface on the cylinder.
  • The following operations are for the steam plate:
    • (1) Chuck up and face one side;
    • (2) drill and tap steam pipe holes;
    • (3) drill corner holes;
    • (4) drill, chip and file the center hole;
    • (5) grind to a bearing surface.
  • Fig. 6 Steam Plate, p. 31
  • No. 27 Drill is 0.1440 inch diameter

Cylinder Heads

  • The first operation on the rear cylinder head was to chuck it up true in the lathe chuck and face off the inside. Next cut back 1/32“ to 2-1/4” diameter. This forms a small projection or boss which will help to centralize the head on the cylinder. Layout and drill holes.
  • The front cylinder head was finished in the same way as the rear with the exception of the hole for the piston rod. When the front head was faced a 7/16“ hole was drilled through the center. A small boring bar was used to true up the hole, after which it was reamed with a 1/2” reamer.
  • The successive operations for the rear head are:
    • (1) Chuck up true;
    • (2) face the side;
    • (3) under-cut the side 1/32“ deep to 2-1/4” diameter;
    • (4) lay out and drill holes.
  • For the front head the operations are:
    • (1) Chuck up true;
    • (2) face the side;
    • (3) under-cut the side 1/32“ deep to 2-1/4” diameter;
    • (4) drill, bore and ream the hole;
    • (5) lay out and drill holes.
    • Fig. 6 Cylinder Head - Front and Rear, p. 28

Valve Rods

  • Two of the most simple parts of the engine were the valve rods. These were made from 1/4“ round cold rolled steel. When the length of the valve rods was determined they were cut from a long bar and a hand die was used to thread each end to the required length.

Spacing Bushings

  • Between the cylinder and the steam plate, small bushings were required to prevent the valve plate from binding. These were made by chucking up a piece of 3/8” cold-rolled steel and turning it to 5/16“ diameter. A No. 27 drill was used to make the hole while the piece was still in the chuck. The pieces were cut off to the proper length with a parting tool. The burrs were filed off and fitted to the exact length when the valve mechanism was assembled.
    • Fig. 6 Engine Details, p. 30

Valve Plate Stud

  • The best method for finishing this part is to center both ends and finish the stud between centers. The operations are as follows:
    • (1) Center both ends;
    • (2) face both ends to the correct length;
    • (3) rough turn to 3/4” diameter;
    • (4) rough turn to 3/8“ diameter, 5/8” from the end;
    • (5) under-cut cylinder end to 1/2“ and rough turn to 5/8” diameter;
    • (6) finish turn all dimensions and square up all shoulders;
    • (7) cut threads on 3/8“ end;
    • (8) cut threads on 5/8” end.
  • In cutting these threads on each end it is best to cut the thread on the 3/8“ end first and fit a nut, then follow the same method as described for the piston rod.
    • Fig. 7 Valve Plate, p. 31

Piston Ring

  • The piston rings for the engines were made up in one lot of twelve rings from a single casting. A hollow casting was made up for this part of the engine and the best mechanic in the class was chosen to do this job.
  • The outside and inside diameters were first turned and the rings were cut off to the desired thickness. When cutting off each ring, the face of the casting was first trued up smooth before cutting another ring. By doing this it was necessary to face only one side after cutting off.
  • After the rings had been faced to the proper thickness, they were sawed on an angle of 30 degrees and the proper amount or approximately 3/16” of metal sawed out. The ring was then fitted into a compression jig and a special arbor was used to finish the outside diameter.
  • The necessary operations are as follows:
    • (1) Chuck up true;
    • (2) turn outside diameter;
    • (3) bore inside diameter;
    • (4) cut rings to thickness;
    • (5) face the opposite sides of the rings;
    • (6) saw out 3/16“;
    • (7) fit in the compression jig, then turn outside diameter.
  • Fig. 6 Pison and Piston Ring, p. 28


  • The piston was grasped in the chuck and a cut taken off one side. The hole was then drilled, bored and reamed to a 1/2” diameter. The next operation was to counterbore one side 3/4“ diameter 3/16” deep. It was then removed from the chuck, pressed on an arbor and turned to size. The opposite side was faced to the required thickness and a 3/16“ groove was cut in the center for the piston ring.
  • The operations are as follows:
    • (1) Chuck up true;
    • (2) face one side;
    • (3) drill, bore and ream a hole for the piston rod;
    • (4) counterbore for clamping nut;
    • (5) press on the arbor and turn outside diameter to size;
    • (6) face the opposite side to size;
    • (7) cut a groove for the piston ring.

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