Stationary Mill Steam Engine



The humble beginnings



 This was a kit from PM Research. It consists of 9 aluminum castings, a bag of various round and hex rods of brass and steel and a blueprint sheet about a yard square. If you try this one I do not recommend it as a first project. The kit is priced at about $60 and you need several expensive accessories to work with it, notably a tilting vise and precision angle plate. It requires both a lathe and mill. PM would have you buy some fine thread taps and dies for this kit, 3-48 and 5-40. I thought that the only supplier around was PM. (I have since discovered that all necesary taps and dies are carried by ENCO at very reasonable prices) They get 3 to 4 times the going rate for taps and dies so I opted to do the whole kit with 4-40 except the hole plugs and set screws which are 6-32 and change from their slotted head screws to socket head machine screws. I like the machine-like appearance of them better. Changing the thread sizes did not cause any particular problems with the kit parts.

One of the changes I made from the drawings was the main shaft. The kit uses a cold rolled steel 1/4 inch rod running in holes bored into the casting. The aluminum is quite soft, definitely not up to 6061 T6 standards. I felt that the shaft would probably rust and would chew into the aluminum. I overbored the shaft holes to 3/8 and pressed in brass bushings which were then reamed to 1/4 inch. I changed out the shaft for drill rod. It runs very smoothly in the brass. When you do this you have to be sure to drill the oil holes through the brass bushings. Another small change was the intake and exhaust tubes. Here again they wanted the fine thread they indicated was a standard hobby size. I made mine from 3/16 brass rod and threaded them to 10-32. At 3/16 the rod is almost an ideal diameter for the 10-32 thread.




 The paint shown on the final model is all powder coating. The .jpg compression doesn't do justice to the colors, especially the red. It does not have the smudges that appear here. Just in case you wondered, it ran beautifully the first time I put air presssure to it. It will run on as little as 5 pounds pressure, but really shows its stuff at about 20 pounds. I don't know the RPM, but I would be afraid to crank it up much faster than it runs on 20 pounds.