Part five by Julius de Waal

Since Bill Hughes first described his Allchin traction engine in 1 1/2 inches to the foot scale in 1957, it has been modelled many times in many scales including 15mm, 2in. 2 1/4in. 3in. and 4 1/2in. and possibly more. Here Julius has the equivalent of a 3in. scale version (but in metric). Builders will be interested that John Rex can supply castings and parts for a 3in. version - see: No doubt John will be happy to build you one, too.

Click on drawings to download - for personal use only.

Although drawings reproduce well on this website, they are even better if downloaded.


Doug Meller from Sydney writes:

Please take this as constructive feedback, I noticed on JDW 3” Allchin drawings the lubricator has a piston of 6mm diameter and a stroke of around 7mm which I would expect to be far too much oil for each stroke of the pump.  On my 3” scale traction engines (2 off) the oil pump piston is 1/8” diameter with a similar stroke to JDW and this provides plenty of oil.

It may be that JDW has scaled up the smaller plans, but there is no necessity to increase the oil pump plunger to this extent.

Other than this I think he does a great job, and as said, I mean no offence, so I hope none is taken.

Ralph Byles from Goolwa, South Australia writes:

I have just seen the note under the advice about the availability of plans for a quarter scale Allchin traction engine.

Castings and other components are definitely available in Australia. See

This is not a commercial venture but rather a group of model engineers making their resources available to other modellers.

We started in 2003 and now have 6 of our engines running with another 12 chaps in Australia and NZ using our components to build their own engine.

Thanks to both - ED.  And look at the guidance on making the boiler from steel on Ralph’s website. As ever, check boiler design with your boiler inspector before starting.