Okay - in the earlier post when he mentioned getting the parts red hot, I assumed it was hi temp silver solder. That is WAY too hot for soft soldering!
Yes, indeed it is. And I'm ashamed to admit that I did it again today, and with the cylinder (!) which led to all sorts of complications. It started off ok, tinning the parts with Baker's fluid:
Suffice to say that my first attempt came apart due to slippage when I tried to join them (using no pins or piano wire, mistakenly thinking that gravity would do the job as the parts are quite chunky), and I lightly clamped (yes, clamped!)
and overheated my second attempt for fear of it coming apart again. The join seems solid, but the cylinder distorted and went somewhat out of round to the point that the piston wouldn't fit into it
. I think this was due to a combination of excessive heating and the pressure from the clamp, which was not huge but big enough to do damage. Why did I clamp it when I had been advised not to? Well, I didn't feel that in my particular case it was acting as a heat sink as my test pieces from yesterday are rock solid. What I didn't take into account was the fact that I was blasting enough heat into the system from a powerful torch to allow the metal to distort even while the clamp and vice pulled the heat away. Never again, I promise.
I tried to rectify this by using the 'flex-hones', which resulted in the bore being too big for the piston! Thinking that I had lost it and that I would have to make a new cylinder, i.e. nothing to lose, I decided to try cutting a groove in the piston...
... and adding an o-ring...
... and to my surprise it's a snug fit and pulls a nice vacuum.
This is just a black rubber o-ring, (from a box by Rolson, size R-04) and I believe that it's not the right kind, but I guess I could change it or use some graphite yarn. However, I'm wondering if I really have managed to salvage the result of a sloppy day's work or if that out-of-round bore will come back to haunt me. If it does, I'll just have to bite the bullet, remake the cylinder and try to learn from it.
Meanwhile, I have been using my Sievert torch for soft soldering. I'm thinking that maybe that's part of the problem. Should I be using a smaller DIY blowtorch instead?
Amazing that one stripped thread can send one on such a long and tortuous journey. And that everything in this pursuit impacts on everything else. And that a single acting oscillator is an easy build yet I'm having plenty of trouble with it. And that I thought soft soldering would be easy, yet I'm having more trouble with it than I have had with silver solder. And that even today, having been given lots of good advice, I was selective about what I followed, thinking it didn't all apply to my particular circumstances...
Sorry guys. Thinking this engine was finished and then having to go back and redo all this has led me into rushing things. Never a good way to go. I will persevere, and slow down...
I'll be making two engines of the same type, but twice the size, when I eventually get this one done. At that point I will follow Tug's suggestion of using pins to stop movement when soldering (though I still have to learn how to do that).
gary