A couple of paddle engines

[malcolmbeak]

Hello steam lovers
Here are a couple of steam paddle engines I made recently. Both are intended to couple directly to the paddles. The larger (photographed on 5mm squared paper) is 3/8" bore and 1/2" stroke. A fairly standard double acting oscillator but photoed with a gearbox at one end to allow for better manoevering. It has turned out to be rather too larger than it needed to be for the model I have in mind, so the smaller engine shown in the photos (this time photoed on 1" graph paper) has been built. It has three single acting cylinders made from thin wall 1/4" dia brass tube with a 1" stroke. It runs very nicely on compressed air - hasn't been tried on steam yet. One aspect I particularly like is that the steam pressure actually pushes the port faces together unlike most oscillators that need springs for the same job. This also means that I could (if need be) use much higher pressures.
Malcolm

[bogstandard]

Malcolm,

Lovely stuff there, especially like the ingenius built up offset crank on the three cylinder one. Did you have much trouble to get it running true?

I don't suppose you have synchromesh on the gearbox, so is it the proverbial crash box or stop the engine first?

Real nice designs.

John

[malcolmbeak]

John
I did have trouble with that crank. This was the third attempt. First off I tried using steel discs for the webs and silver soldering the whole lot. In the past my efforts at silver soldering steel have been pretty useless - same this time. Next a short attempt to machine from solid, but it's a bit flimsy compared with others I've made. I usually mill out most of the throws leaving a small square section to finally turn round, but the long 5/32 slot drill was too flexible. I finally made it as you see. I made a long V block and machined away the central portion, assembled all the bits with loctite and clamped the main shaft in the V. When set, each joint had a taper pin fitted. The centre section of the main shaft cut away and hey presto - amazingly it all works very nicely. I wasn't too keen on fitting 1/8 wide webs on an 1/8 shaft, especially as the fit could not be made too good as the loctite had to have space to work. I'll make another one, but with 3/16 thick webs and a better fit, then try with penetrating loctite instead of the thick stuff.
As you suspect the gearbox is a crash type - dog clutch for forward and sliding gear for reverse. A similar one has been in use for the last 20 years on my open launch. I usually slow the engine rather than stop it although it will go straight between the gears with the throttle wide open!! The design is in the download section under "articles/Malcolm Beak". Why fit a gearbox rather than a reversing engine? Several reasons - with the small engine in the launch (3/8 bore and stroke) I felt that fitting a link system would probably introduce enough lost motion that the already small valve movement would making problematical. Also it is useful to have a neutral position - if the prop gets weeded up, the engine can still be run to keep the boiler topped up. There is automatic water level control fitted.
Malcolm

[gyula]

the steam pressure actually pushes the port faces together unlike most oscillators

Can you explain it a bit? I know how the simple oscillators work, but this is different....

Thanks
Gyula

[malcolmbeak]

Gyula
It isn't obvious is it. Hopefully the sketch will help to explain how it works.
The cylinder pivots about it's head end on the valve shaft. That shaft is only 1/4" diameter, so the movement across the surface is small - about .028". We could use holes marginally smaller than this, but the steam flow would be very restricted. So instead I machined the parts as I've drawn.
Once steam is admitted into the cylinder, it acts on the piston and also in the opposite direction on the cylinder head pushing it onto the valve shaft hopefully preventing any leaks.
Does that make sense?
Malcolm

[gyula]

It sure make sense!
Thanks

[bogstandard]

Thanks very much for that Malcolm, now all explained.

Those sketches remind me of someone else.
A man after my own heart.

John

[malcolmbeak]

Well John - they usually turn out a bit better than that one, but it was done in a hurry to answer Gyula's question.
When I design an engine (anything for that matter) I start with a reasonably scale general arrangement, then all the various parts end up as what I call "dimentioned sketches". Of course some things change as construction proceeds and hopefully the sketches get modified or re-drawn as I go along. Seems to work OK for me.
Do you want pictures of any more of my designs?
Malcolm

[bogstandard]

Malcolm,

What I do, is look at all the different ways things work, and if I don't know, I ask.
Then I see ways of building some of the ideas into different types of engines.

If you go to here, these are my latest finger engines, From there you should be able to access all my vids.
http://www.youtube.com/watch?v=ezOawsPXMns
That will then explain how I do things.
Also I tend to design as I go along, the only problem with that, is that only sketches ever get done, sometimes, not even that, but no full drawings. So if I want two or more of something, they all get built at the same time. You have most probably seen my piston valve build on here, on that I built two in just over two months but at the very end I left one as standard, and customised the second, so producing two engines that are similar but look totally different.

I am trying to build one different type of engine each month, but health issues have held me back for a bit.
But I do have four ideas waiting to be made, including one for building on here if they want me to.

So, finally to answer your question, I would love to have a look at your designs, it would give me more inspiration.

John

[malcolmbeak]

John

You certainly come up with some varied ideas.
I find that I can't design as I go along, I really like to see the whole thing.
All my engines are designed so that they would be suitable for driving model boats, so in general they have to self start. Having said that you will find that some do not - these are in general the ones I made when I started out on the steam trail.
Rather than put the pictures in this thread I will start a new one.

Malcolm