Stainless Oscillating Pistons?

[Stilldrillin]

Did the PTFE piston expand with steam or were you talking about the brass one?

So you pinned the piston then, that's good info to know 

Darren,

This plastic piston lark isn`t quite straightforward........ 

The engine ran perfectly at room temp, on air.

Steam heat expanded the piston, locking it solid, as far as the engine was concerned. 

Piston into lathe, take off "half a thou" per side. Back onto engine....... Several times!

The lathe chuck is "true"....... But not that good, so the piston is not truly round now.

Tried a little `speriment this morning. Dunked a couple of cylinders & machined ptfe into a mug of boiling water.
Got it to slide in one cyl. But not in the other (which has a thinner cyl wall).

Measured o/d when cooled....... It`s only .001" or so below std (.3125")!!! 

I get different readings from mic & vernier. Also depends weather the sun`s shining or not....... 

I think I`ll have to steam individual piston/ cyl sets before mounting to the 3cyl engine...... 


The piston s are tapped 1/8 Whit & screwed onto the rod, with a spot of loctite.



David D

[sbwhart]

David

One Little trick we use to do with nylon parts was to boil them, just like an egg, many plastics take up moisture and grow, I know that with nylon it can take up to about 1% of its own weight, don't know what it is for PTFE but you could try it before you machine to size.

Cheers

Stew

[Stilldrillin]

David

One Little trick we use to do with nylon parts was to boil them, just like an egg, many plastics take up moisture and grow, I know that with nylon it can take up to about 1% of its own weight, don't know what it is for PTFE but you could try it before you machine to size.

Cheers

Stew

Sounds good to me Stew! 

I`ll try anything....... 

The used plastic piston measures around .309".
The boiling water plug measures around .312".

I guess steam is hotter than boiled water...... And it shows in the differing diameters!

David D

[Darren]

I did mention plastics absorb water, I didn't think it was that much though !

[bogstandard]

So now you lads understand when I go on about the correct materials for making cylinders and pistons out of.

That is why I always ask if it is going to be run on just air or steam. It makes a very big difference.

Darren,

If you are going to make the twin engine for running on steam, I would stay with the recommended metals. David's engine is a lot different in design, and yours will have a lot more heat, friction and stresses involved. You could modify my design to use PTFE piston rings, but I don't think there would be any advantage over the standard o-rings.

John

[Darren]

Thanks for the tip John, I will go with metal then 

I don't intend to run it on steam, but someone might when I'm gone 

[bogstandard]

Darren,

When you are gone, the least you will be worrying about is whether someone is going to be running your little engine on steam. Make it for yourself, no-one else. Unless of course you are thinking of taking it with you.

I was thinking about taking my mill and lathe with me, can you just imagine the Co-op pall bearers trying to move those, with my weight as well.

Mind you, I suppose I could get a few jobs doing furnace repairs, or maybe even a new set of gate hinges.


Bogs

[Bernd]

   If I were going that way and taking my machines along I would make a coal stoker. To labor intensive shoveling all that coal.   

    

Bernd

P.S. 

[cedge]

Bernd
I doubt John would require a stroker, where he's likely to wind up.... but topping off the
a bit of a tough job...(grin)

Steve

[Bernd]

Ah Steve one of us spelled "stoker" wrong. 

I had to go back and check my spelling.

[Stilldrillin]

I machined a piston to a sliding fit in one of the triple`s cylinders, then took off .001" per side.....

Assembled the assembly to the single cyl engine & steamed it to prove it worked ok.

After proving, each set was then assembled to the triple...... 

Well, it all went perfectly........ 

I lit the burner. After a few mins it just started, on it`s own! 

I throttled back to tickover & grabbed the camera.........



After a few minutes running it would tick over very sweetly......




After some time, it  STOPPED!!

The solder had melted on the regulator!  :shock:




I think the burner is a little too enthusiastic for tickover mode!

Now re soldered, with a heat shield fitted........



Will try out a smaller "tickover" burner, at Lincoln.

It`s all an experiment.......... 

[sbwhart]

That was excellent David:-

Great Job,

Great Video,

Great Tomato Plants
 
     

Unfortunately I'll miss it at Lincoln we hit the plastic hard last week in Edinburgh and the bills just landed 

                                                                                                                                                 


So enjoy the rabbit pie at Browns

and I'll look forward to meeting you at Arrogate


Stew

[Stilldrillin]

Thanks for that Stew.

This engine just keeps on developing....... 


A pity we`ll not meet at Lincoln, it should be a great get together.

Some of the "all weekend" members have set off, already!

Hope to see you at Harrogate. 

David D

[bogstandard]

Very nice indeed David, it ticks over like a swiss watch.

You've just got to wait now to see how the pistons stand up to real extended running. I shouldn't think you will have any trouble.

John

[Darren]

You're not wrong there David...

That is sweet, those pistons will last a lifetime or two I guess....

[Bernd]

Sweet running and sounding engine at tick over there David. 

Full throttle sounds like a race car. I wouldn't have thought it would run that fast. Pretty vibration free too from what I saw.

Bernd

[SPiN Racing]

Wow very very cool engine.
The sound ot the three humming away is really a nice tone at full song.