Machining from Castings

[lovenyc2600]

Is there any hint in kozos book on building the Pennsy A3 Switcher, on how to machine from castings?

I know it is supposed to be easier to machine from castings, than building from the ground up but this from a complete novice.

As far as castings go, I am not sure where I would begin.

[kvom]

If you're a complete novice than doing as kozo advises and building the tender first will give you a lot of useful experience for building the engine.

Machining CI is like other metals in that you use similar tooling. The main differences from brass or aluminum are:

1) Feeds and speeds are a lot less (CI is pretty hard); at proper speeds CI machines quite easily. No lubricant is needed because of the carbon in the metal.

2) The swarf comes off in very fine grains that are quite messy.

Kozo shows machining sequences for the drivers. I was advised that for the first step, chuck in a 4-jaw with the outer face exposed and adjust so that the inner rim (where the spokes join) runs true. This will make it look better when actually running. Then turn a flat tread area as a chucking surface for phase 2.

Next, reverse the drivers and chuck on the flat tread area. The 3-jaw chuck is fine for this. face the inner side and then drill/bore the axle hole, which will now be perpendicular to the inner side. I preferred to ream mine rather than bore.

Now you need an arbor/mandrel set up to mount the wheel for turning the tread and flange and facing the outer side. Kozo shows this side very well. The final stage is drilling/boring/reaming the crankpin holes, using either a fixure as Kozo shows or else another method for ensuring a consistent distance between the crankin hole and the axle hole.

For the cylinder castings, you would use a 4-jaw to center on the bore hole and then bore out to the correct diameter. With the same setup one cover surface would be faced. Now there are two datums: the bore and the face to mill/turn the other face and the two flat surfaces that connect the steam chest and tee. It's not clear to me that machining from a cylinder casting is easier than from raw stock, and a mistake will be more costly.