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Shop Notes 1/15 - Machining more steam engine parts

HakasaysJan 16, 2022, 12:53:22 AM

Last I left off with the crank rod partially completed and sitting in the milling machine.  This basically just needed some precise cleanup operations on all the sides, to let it fit onto the crank pin and soon-to-be machined crosshead.

And finished.🤗

I attached the crank rod to one and and ran it in a bit with the cordless drill for a couple minutes to help wear it down into a better fit.  Believe it or not, even a ten-thousandth of an inch can make a huge difference for such things.


I had a good setup plan in-mind so I did the inboard head next

(inboard head keeps the piston lined up and sealed in the cylinder).

As always when working with castings, the first important thing is to get a good reference surface to build from.  Here I'm taking many light passes with a face mill to get a nice flat surface.

After that, I set the CNC for conversational and made a quick layout to machine a boss to match to the cylinder.


I left that running for a good hour or two (better to be too safe than run too hard and break something or ruin the setup) so in the meantime I figured I'd churn out another lathe part.

This part uses some teflon packing to keep the valve rod sealed against the steam pressure.

Drill a hole, tap a hole, turn down the hex into a square shape, and part off.  Not too difficult, and no really critical dimensions.


Inboard head was finished, so I could finally do the operation I had running through my mind this morning.

The machined face of the inboard head was mounted to a piece of aluminum scrap with superglue, using plenty of pressure against the center hole to align everything perfectly.   I've used this method to re-machine pistons, and they usually come out without 1-2 tenths (0.0001 to 0.0002 inches).  Super precise for a really quick setup.

Almost finished with this part, finally.  Just a little more cleanup and it will be ready to fit to the cylinder.

Tomorrow will be test-fitting the piston and head to the cylinder, then starting work machining the crank pin guides (simple alternative to using a crankshaft, especially in the days these engines were designed)

Current build progress.  Coming together pretty damn fast compared to the engine I machined last year.
Like learning any new skill, first time takes a day, second time takes an hour, 3rd time takes 5 minutes.


Hope you enjoyed🤠