Making “Forged” Crankshaft Complete

Back in the day traction engine crankshafts were forged from round(ish) steel bar. Thus the webs of the crankshaft had characteristic rounder edges and corners – not at all like  crankshafts with webs made from rectangular stock.

This is what the rounded webs of my crankshaft for the 3/4″ scale Bassett Lowke model traction engine looks like:-

Closeup of Crankshaft Journal Completed

Difficult Job

It is generally accepted that making a forged-looking crankshaft as seen in the photo above is, for the average model engineer, a difficult or even impossible task, especially in small scale models.

In his book “Allchin” (making a 1 1/2″ fine-scale model of a Burrell Traction engine, the author W J Hughes, describes a process of cutting the crank from a flat steel plate and forming the rounded webs by filing. Apart from the inherent time-intensive and difficulty of doing this there is one inherent property of the cranks that makes this process virtually impossible.

This is the fact that it is impossible or at least extremely difficult to gat a decent sized file between the webs without the fie rubbing on the web on the other side.

My Unique Solution

My solution to this difficulty is described below and this also eliminated a great deal of the filing required, to get the rounded finish on the crank webs. I have not seen this method described anywhere else.

Photo Gallery 01 – Comparing Crankshaft Types

Often in models crankshafts re of the ‘slab’ or square type. That means that the crank webs are made from flat rectangular bar with square ends. The picture gallery below shows the difference between this kind of crankshaft and the rounded ‘forged’ type of crankshaft I adopted for my model.

The Process of Making a Model Forged Crankshaft

The photo galleries below show the process of making a model traction engine crankshaft to a small scale (3/4″:1ft) with a forged appearance.

The next gallery shows the W J Hughes method of machining the crankshaft for the model 1 1/2″ Allchin traction engine from flat bar. Note that the flat bar has to be filed to represent a forged crank. Note also that it is twice as big as my crankshaft.

Photo Gallery 02 – Allchin Crankshaft Machining