This was my first steam engine build.

First task was to get hold of a slice of mild steel for the flywheel. I was not going to start something and then find out I could not get hold of the material for the flywheel.  It's 200mm diameter and 50mm long. It cost me 74 Euro and that includes the cutting of the slice (45 Euro). The cutting was more expensive than the material!  I guess beggars can’t be choosers.

I decided to use Metric, using direct conversions (1"=25.4mm) from the original drawings. The clearance holes and tapped holes will be Metric.

Blued up the best face of the material and using a divider marked the flywheel with spokes so that I could see where I could drill the mounting holes.

I decided that it would be a good idea to face off the other side before.  So I clamped it to the mill table and put a 20mm end mill in the collet to start milling that face. That's when the first problem cropped up. I do not have enough Y axis travel to reach all parts. This flywheel is going to stretch the capabilities of my poor Chinese 3-in-1 lathe and X3 mill. I remembered I had a fly cutter which I very rarely use because I never get a nice finish. I tried it and I could reach the top and bottom of the face. I was not worried about the finish because I would still be machining this same face on the lathe.

Set out the four mounting holes...

...and drilled with a deep counterbore for the Allen head bolts.

I bolted the flywheel material to the faceplate and managed (that was heavy) to fit it to the lathe. Experimented with various tool post configurations to get it as close a possible to the face.  Set the lathe to its slowest speed (160 RPM) but was having some doubts if this is slow enough for this diameter.  Looked it up and I got an RPM of about 50 if using HSS tools.  Good thing I am going to use carbide tools for hogging it down to size.

Made a first cut on the OD to see if I had enough reach...

...and the face with a different tool configuration.

I could reach (just) all areas.  Now to start hogging the thing and hopefully the lathe spindle bearings won't give up the ghost (keeping my fingers crossed).  Thankfully, the material is nice to machine.

The OD of the flywheel is finished 0.1mm oversize for clean up.  The excess material has also been faced off. Left about 1mm to be faced off from the other side.

The face has been marked to be recessed.

One side of the flywheel finished.

Made a sub-plate and fitted it to the face plate and centred it as much as possible.  Skimmed the side and the face of the sub-plate and then drilled and bored the 10mm hole in the center for the drawbar.

Made two registers; one for the hub in the centre and another one for the rim.

Fitted the steel flywheel to the sub-plate and it will be held in place with a drawbar.

Started hogging the other side of the flywheel.  No slippage up till now.  I made a witness mark between the flywheel and the sub-plate to check for slippage.  Fingers crossed.

In preparation for milling the flywheel, I needed to drill and tap four 8mm holes in the sub-plate.  I used the four holes in the flywheel as a drilling template to mark the location on the sub-plate.

Removed the flywheel and started drilling and tapping the four holes.

I have a habit of protecting a freshly made tapped hole from swarf by screwing in an appropriate bolt.

Part two here