This little engine is an adaptation of the "Minikin" by Dr. James R. Senft. The plans can be found on page 54 of Steam and Sterling Engines. This book is available from The Village Press and a few other suppliers. The original engine had a 1/4" bore and stroke. To make the engine more visible, I scaled everything up by 2. This engine has a 1/2" bore and stroke. The cylinder and standard are machined from acrylic or Plexiglas. There are a few tips you should know about machining this material. It is very sensitive to oils and solvents. Many fluids found around the shop can craze and destroy your project in a matter of minutes. Wipe down chucks and vises to prevent this. Even soluble oil can cause a piece of acrylic to crack and fall apart, it's amazing. For a coolant, use water, or water with a small amount of dishwashing soap, or, as I did, a water based cleaner made for acrylic sheet. To polish tool marks from flat areas, first sand them using 400 grit wet and dry paper of a flat surface. Use water on the sand paper to improve the finish and prevent clogging the grit. After a few strokes on 400 move to 600 grit. For final polish, wipe a stick of polishing compound on a fresh piece of paper, like as if you were using a crayon. With the paper on a flat surface, rub the part against it. This will put a nice polish on the part without rounding the corners or putting waves on flat areas.
