Making A Crankshaft -1

by John

In a previous post I explained how I replaced a broken roll pin in a fabricated traction engine crankshaft. The repaired crankshaft worked well enough for the renewal of the boiler certification, but I suspect that one of more of the other roll pins is also damaged.


… there is still a flywheel wobble of about 1mm at the rim. 1mm does not sound much, but it looks horrible. So I have decided to make a new crankshaft. Using a single piece of steel.

The crank-shaft is at the right of the photo, beneath the big ends, eccentrics and main bearings.

For the third time in a couple of weeks I removed the crankshaft from the engine. The first time took me more than 4 hours. Second time was quicker. Today it took me only 93 minutes, including the time wasted looking for small open enders.

And meanwhile I bought a chunk of steel big enough to carve into a replacement crankshaft….

That lump of black steel is 90 x 90 x 420mm. It weighs 26kg! The faulty crankshaft to be replaced in front. The gear and the eccentrics will be removed in the next workshop session. And the original plans of the crankshaft at rear.

The crank-shaft has two cranks, at 90 degrees from each other. The shaft itself is about 26mm diameter.

My plan is to use the milling machine to remove most of the waste, then to finish the accurate diameters on the lathe, turning between eccentric centres.

It is apparent, looking at the size of the bar, that most of it will end up as swarf. Oh well. On the floor it will keep the tigers out of the workshop.

I will post photos of the stages as they happen.