Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Gentlemen,
It's been awhile since I posted by as you know life sometimes gets in the way. I have been busy in the shop with various projects, the latest of which is the Benson inverted steam engine. The drawings for this engine are freely available on line. As is my habit I don't always build to drawings so I scaled the engine down by 1/4. This made the smallest bolts and nuts M1.0 x .25 and the largest 0-80 Imperial. The brass is 360 and the steel parts are all 303 stainless. The flywheel is 5.562 diameter and not having stock that size I fabricated it. I did a layout in CAD and created 4 segments for the rim. They were cut as rectangles with the ends cut at 45 degrees. They were clamped together and silver soldered. After cleanup I chucked them in my 4 jaw chuck and cut the diameters leaving a little on the outside for cleanup after assembly. The governor is driven by helical gears. On the original they are both the same size but in watching the videos on Youtube I noticed that the engine needed to be spun quite fast for the governor to operate so I decided to use a larger gear on the crank to increase the speed and hopefully make the governor a  little more sensitive. A fellow on one of the other forums has created several spread sheets for cutting gears, spur, miter and helical. Using his work sheet I came up with a ratio and diametral pitch that would work. The center to center distance only varied by .002. In making helical gears each gear needs it's own helical template based on the D.P. and P.D. Once fabricated they are basically throw-aways a they can only be used for a specific gear. With all the helical gears I've made I'm up to about 15 templates in my box. Usually when making larger steam engines they are assembled with studs and nuts to replicate the full sized versions but when making engines this small I cheat and turn a small projection on the bolt to resemble the stud sticking out. 
I apologize for the double post but I didn't notice someone else had posted the Youtube link to this video until I started reading other posts. 

 

Hi Ian,
With the small scale of the engine I was limited to how small I could make the gear on the governor and still maintain the center spacing so the gear on the crank is 17 teeth and the gear on the governor is 14 teeth so the ration is just around 1.25:1. Not a great increase but a little faster. In the video when I increased the engine speed the engine is running on the governor. This is with about 20 psi. It will run on only a couple of pounds but it won't get up to governed speed. When using governors on these miniature engines the governor has to overcome the friction of all the links and valves which no matter how small they are the balls will fly out it's when the speed is brought back down that the weight of the balls isn't enough to bring the governor back to rest. On this one I added a .06 I.D. spring wound from .008 music wire. I kept stretching it out until it worked in both directions, flying out and returning. It's a fine line on something this small.
gbritnell
As a side note I had mentioned about the spread sheets that a contributor to one of the other forums had created. I opened up the sheet and kept plugging numbers in, D.P. and tooth count until I came up with the final numbers that would meet the center to center spacing. I needed to maintain this because I had already machined the entablature for the crankshaft and governor pocket. In hind sight I should have done my gear calculations prior to machining the governor pocket then I could have probably got the governor to spin a little faster.

George, Thanks for posting more details. Sorry did not mean to share your work before you got a chance, saw video when it had 16 views. Truly a work of art.

Amazing work, George!

Hope to see you at the Columbia show this weekend.

Really great! Thanks for the topic and the video.

Where are the drawings for the Benson available? I want to make the governor for another engine. If it is not available online, could you take a pic of the governor parts for me? Thank you.

Stunning work George!!