Drive Springs

kiwi2 · Jul 14, 2015

Hi All,

About 7-8 years ago I bought a set of castings and a set of plans for a Traction Engine relatively cheaply from a firm called Steamech which was based in Christchurch here in New Zealand. From what I can gather the company has since ceased trading (I think that was the reason for the low price).
At the time I bought the plans and castings I was pretty sure that constructing the traction engine was beyond my capabilities so everything has sat in a box gathering dust ever since.
In the meantime I have completed half a dozen or so stationary engines and become a bit more skilled and in a fit of optimism have decided to take the Traction Engine on as a project.
One of the things I'm not sure about is an item in the drive chain which is referred to as a stainless steel drive spring which connects the drive pulley from the engine to the pulley attached to one of the rear wheels.
I can't find a supplier for these and wonder whether they are obsolete technology.
Does anyone know anything about drive springs and whether they offer an advantage over using say an O ring as a pulley?

Regards,
Alan C.

Cogsy · Jul 14, 2015

If it's a spring being used like an oring between pulleys, I would guess a possible advantage would be the 'adjustability' of a spring vs an oring so centre distances wouldn't be as critical. Just a guess really.

A possible source for these springs would be the lip springs from oil-seals. They come in a massive range of sizes and can probably be sourced for free from old, scrap oil seals (maybe a truck repairer). I've personally seen lip springs from 1/2" diameter up to at least 20".

kiwi2 · Jul 14, 2015

Thanks Cogsy,

I hadn't thought of oil seals. In the meantime I've found a site selling Mamod bits and pieces which sells drive springs - http://www.mikes-steam-engines.co.uk/for_sale.htm
As far as centre distance is concerned, if I were to use an O ring I'd make one to fit using loctite and a length of rubber.

Alan C.

Blogwitch · Jul 14, 2015

Alan,

I am sure you could obtain the Mamod drive springs much cheaper off Ebay.

If one is too short, they are made so that you can join two together, or even just part of one so that you can get the correct length.

If they are too small a diameter for the grooves, I do have some about 4mm diameter that I could let you have.

John

kiwi2 · Jul 15, 2015

Thanks John.
The price for a drive spring on the link I quoted is only one pound fifty so price isn't really an issue. Thanks for your offer of a 4mm spring but the pulley attached to the drive wheel only has a width of 1/8" (3.2mm).
What is your opinion regarding these drive springs - Do they offer any major advantages over an O ring?

Regards,
Alan C.

tornitore45 · Jul 16, 2015

They transfer only an infinitesimal small torque. They were used to connect simple moving accessories to steam engine, motion without torque.

To actually move a traction engine I would substitute an O ring and is necessary fit a tensioner.