Another Oscillator

[PaulR]

After only reasonable success with the Stirling engine and a failure of the valve-through-the-piston failure I've decided to stay on safer ground for the next build, especially as I'm busy with other things at the minute. So having only sketched out a basic plan on paper I'll mostly be winging it as I go along so mistakes will happen(TM). It'll be a double acting inverted vertical engine (at least, I think that's what a flywheel-at-the-top engine is called!), 8mm bore, 15mm stroke. I wanted to make something a bit bigger but don't have any brass bigger then 3/4". I did think about making a composite cylinder with a brass tube and steel ends (with a brass insert for the rod guide/gland) but it's too much faff for the little free time I have.

Made the basic cylinder and turned down the ends to solder on the flanges later. Then the home-made Heath Robinson dividing device got its first outing, to mark out the holes for the flange screws. As these are identical I'll make a double thickness one (plus a bit) then part if off down the middle.

If I can find a suitable piece of steel pipe I fancy having a go at fabricating a very basic flywheel this time around, just a plain rim and hub with circular spokes.

[PaulR]

Made the flanges and the easy cylinder cover. Even went crazy and added a decorative recess  Got the port block to length but I want to make it about half as deep
Here it is so far with some temporary screws and a length of tool steel posing as a giant piston 

I was planning on making some studs and using stock nuts to hold the covers on but they're a bit too big and overlap the edges by about 0.5mm. Annoying. I could either buy some 1/8 hex and make some nuts which being ~3.6mm across will fit while not leaving much meat around the M2.5 thread or buy some cheese head screws and turn down the head a bit if necessary.

[vtsteam]

I really enjoy reading about your experimental engines. Definitely fun! Don't worry about the mistakes. I never make any, of course......

[PaulR]

I really enjoy reading about your experimental engines. Definitely fun! Don't worry about the mistakes. I never make any, of course......

Thanks!

[Jasonb]

1/8" (3.175mm) hex will work with M2.5, I've done it with 3mm hex at times but usually have 3.5mm nuts on M2.5

[PaulR]

... I've done it with 3mm hex at times...

Blimey that's tight! I needed some 2.5mm screws anyway so I've taken the easy option for now 

[PaulR]

Made the other cylinder cover.

Initially I though I'd do it 'properly' with a gland nut and packing or an o-ring although I'm not even sure if that's a proper use for o-rings? If it is, future me would like to known if a flat bottomed hole would be essential or whether it would work ok in a drilled (and internally threaded) hole like this bad drawing?

Either way, I found it would it would be difficult to fit in so went for a simple rod guide.

Also did my first bit of simple milling with the vertical slide, thinning down the port block. No dramas and the finish wasn't horrendous  Next I think I can solder all the bits together then sort out the ports and pivot.

[crueby]

I use o rings (viton 1/16" cross section is my preferred, longer lasting than some of the other rubber materials) on all my steam engines. A flat bottomed hold would be preferable since it won't pull in the ring as the rod goes in, but its not essential. For the outer gland to retain the o ring, I've used both threaded posts and ones with flanges with screws out on the surface of the block - both work fine. You want to pick an o ring size that is a snug fit on the rod. A little oil on the ring will keep it moving smoothly. I also use viton rings for piston rings in all my engines.

[PaulR]

I use o rings (viton 1/16" cross section is my preferred, longer lasting than some of the other rubber materials) on all my steam engines. A flat bottomed hold would be preferable since it won't pull in the ring as the rod goes in, but its not essential. For the outer gland to retain the o ring, I've used both threaded posts and ones with flanges with screws out on the surface of the block - both work fine. You want to pick an o ring size that is a snug fit on the rod. A little oil on the ring will keep it moving smoothly. I also use viton rings for piston rings in all my engines.

Thanks Chris, yes the pulling in of the ring was what was bothering me. Next time I'll plan ahead better and maybe use a D-bit to do the flat bottomed hole. I have some 4.2mm ID rings which seem to fit ok on 4mm drill rod (but I don't quite see how!).

[crueby]

I use o rings (viton 1/16" cross section is my preferred, longer lasting than some of the other rubber materials) on all my steam engines. A flat bottomed hold would be preferable since it won't pull in the ring as the rod goes in, but its not essential. For the outer gland to retain the o ring, I've used both threaded posts and ones with flanges with screws out on the surface of the block - both work fine. You want to pick an o ring size that is a snug fit on the rod. A little oil on the ring will keep it moving smoothly. I also use viton rings for piston rings in all my engines.

Thanks Chris, yes the pulling in of the ring was what was bothering me. Next time I'll plan ahead better and maybe use a D-bit to do the flat bottomed hole. I have some 4.2mm ID rings which seem to fit ok on 4mm drill rod (but I don't quite see how!).

4.2 equals 4,  sounds like the old joke, "2+2=5 for sufficiently  large values of 2"

[PaulR]

I use o rings (viton 1/16" cross section is my preferred, longer lasting than some of the other rubber materials) on all my steam engines. A flat bottomed hold would be preferable since it won't pull in the ring as the rod goes in, but its not essential. For the outer gland to retain the o ring, I've used both threaded posts and ones with flanges with screws out on the surface of the block - both work fine. You want to pick an o ring size that is a snug fit on the rod. A little oil on the ring will keep it moving smoothly. I also use viton rings for piston rings in all my engines.

Thanks Chris, yes the pulling in of the ring was what was bothering me. Next time I'll plan ahead better and maybe use a D-bit to do the flat bottomed hole. I have some 4.2mm ID rings which seem to fit ok on 4mm drill rod (but I don't quite see how!).

4.2 equals 4,  sounds like the old joke, "2+2=5 for sufficiently  large values of 2"

  4.2 is what the label says, I didn't try to measure it with a vernier... my delicate touch would have made it at least 5 

[PaulR]

Made the piston and rod.

[Sanjay F]

Blimey Paul, you are motoring, looks great BTW 

[PaulR]

Blimey Paul, you are motoring, looks great BTW 

Cheers!

Another outing for the milling slide this evening, just to put a 6mm wide flat on the cylinder. Pretty much ready for soldering now, just need to ease the end flanges a bit first as they're too tight a fit. Must also  remember to keep the holes at each end lined up when soldering, might look a bit odd otherwise...

[PaulR]

What an annoying session today! Soldered the end flanges on with the holes all lined up nicely. Soldered the port block in place. It was parallel to the cylinder axis but slightly offset to one side. Desolder and clean up. Tried again, this time it came out slightly skewed to the axis. Desolder and clean up. Tried again, this time it was offset again, maybe 0.5mm. Desolder and clean up. Fourth time lucky, finally got it lined up to my satisfaction.

I wasn't able to flip the part over during soldering so there's no solder between the end flanges and the block in places. Don't think there'll be any leakage but I might fill the gap later. Poor little cylinder was burnt to bu**ery and I had to run the hand reamer through again to get the piston to go in.