Hi all,
Having already built a SOSE based on the original plans, see
http://hobby-machinist.com/index.php?topic=3084.0, I thought I would share some comments about difficulties and changes I made; I didn't stick to the dimensions on the plans if the available materials made it easier to work with slightly different ones, but that's not what I want to talk about.
1 - I think the most important change, the one that I think makes a real difference, is the cylinder pivot. I think that it is very difficult to ensure that it is perfectly perpendicular to the cylinder face if it is just screwed on, as for the plan. I decided to make it plain and just Loctite it perpendicular to the cylinder; I did this chucking the pivot in the drill press, with the cylinder in the vice, holding on to the drill press' handle for 60 sec.
2 - I also chose to use a collar, rather than a nut, to compress the spring, so that the pivot became just a 4 mm diameter cylinder.
3 - The cylinder head was also Loctited, because I think this makes a better seal than a bolted one; of course it cannot be removed, but why should I want to do that?
The following changes are merely cosmetic.
4 - The piston stem has non-uniform thickness because I wanted to test my ability to turn curves without a ball turning attachment; OK, I'll tell you how I did it. I have a Norman Patent tool post which I rotated by hand on it's post, then I finished the surface with sand paper.
5 - The frame has rounded sides, just to make it different.
6 - I later decided to make the spoked flywheel that is illustrated in the thread above. Since this has a larger diameter than the original, I had to file the spring collar opposite to the grub screw, to make room for the wheel.
7 - I made the main bearing with brass, because I couldn't find phosphor bronze, but I intend to replace it sometime in the future.
Last but not least, it is important to lap the cylinder and frame faces for them to match perfectly.
I hope you enjoy it as much as I did. ;0
José