Medium sized wobbler engines.

[Gas_mantle.Participant @gas_mantle]

[Gas_mantle.Participant @gas_mantle]

Hi all,

At the moment my main ongoing project is building the 'Potty mill' engine but I quite fancy the idea of building a slightly larger than normal wobbler engine as a bit of fun whilst doing the Potty mill.

I just wanted something very simple with no frills but something with a bit of 'oomph' that makes a lot of mess and noise. Nearly all the wobblers I see online are either the very small 10 -15 mm bore or very big but I wanted to make one perhaps about 40mm bore.

I realise wobblers aren't efficient so wouldn't expect to see many in larger sizes but wondered if there are any hidden problems with building a 'biggish' one. I only want one as a bit of fun and not bothered how efficient it is so is it practical to simply scale up the simple design of the 10mm bore ones ?

I'm about to build a rudimentary boiler that will ultimately (hopefully) power the 'Potty mill' so I'd really like another slightly bigger engine to test things out and generally have a bit of a play around whilst seeing what my boiler is capable of.

Many thanks

Peter.

Edited By Peter Nichols on 16/09/2015 16:11:17

[David Clark 13Participant @davidclark13]

There are videos on you tube of someone building a large aluminium oscillating engine that are worth watching.

[Neil WyattModerator @neilwyatt]

> I realise wobblers aren't efficient so wouldn't expect to see many in larger sizes

Then you aren't looking in the right places

Paddle steamers are a good place to start:

Neil

[Gas_mantle.Participant @gas_mantle]

Hi David,

I've trolled youtube but the only thing I can find is Tubalcain building a pretty big 'A' frame one that's too big, do you have a link to the aluminium one please ?

The only mid sized wobbler I can find is the one we spoke about in an earlier thread, this one :-

**LINK**

It's about the size I'm interested in but as a beginner I just want to build a very basic one, would an engine of this size (I'm guessing its about 35mm bore) work ok mounted from one side of would I need to build a cradle like the one in the video ?

Peter.

[Gas_mantle.Participant @gas_mantle]

Hi Neil,

You posted as I was typing my reply to David.

What I was getting at when I said they aren't very efficient is I meant for someone like me who has a lathe but not a mill can I simply scale up a very simple 10mm bore wobbler to say 40mm by keeping to roughly the same proportions ?

A 40mm bore wobbler done without a mill isn't going to be an engineering masterpiece but I only want something that willl turn a 5" or 6" flywheel whilst making a lot of noise an mess.

I just thought it would be an interesting bit of fun to build something very simple on a bigger scale.

Peter.

[David Clark 13Participant @davidclark13]

The tubal Cain one is the one I meant. If you look at the design, you will see it is basically the same as a small one so just double or treble the size of a small one.

[Gas_mantle.Participant @gas_mantle]

Hi,

Thanks David, I have some 2" round stock that ought to give me 35 – 40mm bore once I machine off a face for the ports. I'll give it a try and see what it turns out like.

I'm not really sure how much steam something of that kind of size will need but it's an experiment to get a bit of machining experience and have a bit of fun at the same time.

Peter.

[Ian S CParticipant @iansc]

I imagine it would take quite a bit of steam/air, but with a reasonable size of flywheel, it could be made to run quite slowly, and be economical on steam.

You say small 10/15 mm bore, I say small 3 mm bore.

Ian S C

[Gas_mantle.Participant @gas_mantle]

Nice little engine Ian, I bet that gets up a good speed

I thought a longish stoke would slow it down a bit but would the reduction in speed still require the same amount of steam by virtue of powering a greater cylinder capacity ?

Peter

[Ian S CParticipant @iansc]

Can't remember without going out to the workshop, but I think it's either 5/16", or 8 mm, and any pressure above 20psi, and it sounds like a bumble bee, and if the pressure goes up a bit more there is quite a gap between the cylinder and the valve face. I did have it in a little tin tug boat about 11" long.

Ian S C

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