E.P. Allis 3000hp Quadruple Expansion Corliss Engine, 1893 in 1/12 scale

Quote from: ChipswitheverythingWhat you are showing and describing in this engine build, the casting, machining, the holding jigs and process involving very modern methods, is really remarkable, and at a pioneering end of model engineering. This will eventually be a most impressive and mighty model engine!  Dave

That's high praise indeed! Thank you for the kind words. It's going to be a very long road but it seems doable so far.

Quote from: pgp001That flywheel makes mine look like a baby at only a foot diameter.

That is such an impressive piece of work! I was actually going through your thread a while back to see how you were handling the rim segments. The details are fantastic.

Quote from: CII was reading this very interesting thread, and was scratching my head, saying "You know, there are not many machine shops that have an iron foundry in them".
I like to keep up with who is doing what iron casting, and where.
Then I looked at the angle iron on top the flasks.
I only know of one iron foundry that does that regularly.
This thread has a K.S.W. feel to it for sure; it can be no other.

Great design and castings !

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Ha! I didn't realize it was that distinctive. Got it in one! That's hilarious.

Flywheel Rim First Cuts

The initial flywheel rim segment casting ended up swiss-cheesed with inclusions, but externally dimensionally correct, so this one was chosen as a setup part to validate the machining workflow. With the flat surface established, the part was indicated square in the mill based off of the sides of the central rib, and one outer edge skimmed to clean up. That done, it's over to the surface plate to lay out the slot to be milled down the center where it will interface with the spokes.

Part of what makes these components challenging is that the key aspect is for the geometry of each casting to line up well with its neighbor at the interface to the next segment, but none of the features are particularly flat or square. In this case, the centerline of the casting was determined by finding the middle between the two corners where the arcs at the ends meet the center ribs.

Back in the mill, most of the material was removed with a solid carbide 5/8" roughing mill, which performs incredibly well in this material and can take massive bites without the machine complaining at all. Finishing was done with another carbide 5/8" 4 flute, this time with a 0.060" corner radius, for a nice look that matches the radii on the rest of the casting. The surface finish came out excellent, and I was able to sneak up on the finished slot width of 0.751" by checking with gauge blocks for a half thou or so of clearance with the spokes.

Rim Segment Machining Fixture

Sometimes, proper workholding is a whole project all on its own. Another critical part of getting this assembly to go together correctly is achieving the correct 30 degree angle between the end faces of the rim segments to a pretty high degree of precision, as well as the distance between the faces. Once the spoke bolt holes are drilled in the casting, this fixture establishes from them the end face angle and end face position, as well as providing locational reference for the 8 #10 bolt holes that join each rim segment to its neighbor.

I lucked into some freebie raw material - at least a half ton of 2" thick machined steel plates from a local automotive manufacturer. No idea on the alloy, but it's stout stuff. A long, LONG time on the bandsaw, then back and forth between the mill and the surface grinder flattening and squaring up to establish nice references and cut some pleasing chamfers. The critical dimensions here are the thickness of the web where the casting mounts, which also needs to be centralized relative to the outer faces of the fixture. To simplify getting this right, I built a gauge block stack at the correct theoretical height of the web off the surface plate, and when both sides of the web matched this height I know I'm good (double checking the web thickness with a mic for the last few tenths).

Finally it's back to the mill to make the two mounting holes for the part - position matters a lot here, as that is the fixture's whole job. For jobs like this (relatively small, very precise holes) I really like a solid carbide boring bar in the 2" Criterion boring head (plus a shop-made extension). Sub thou precision is easily achievable, and locational accuracy is very good. I had multiple full days of work in this part spread out over several months, so it was a good feeling to hit the numbers and have it come out well.

Rim Segment - Bolt Holes and Ends

To drill the spoke bolt holes, the part has to be referenced in two more directions. It goes in the vise now, since we've got good reference surfaces on the back face and one edge, and referencing the center web geometry like we want gets a bit awkward to reach past the outer bits of the casting. A wiggler is used to pick up the edge at opposite points to find the centerline in the X axis, and then at that center we need to pick up the web surface in Y. The edge finder isn't long enough to reach directly, so a 123 block is used as an intermediary. I don't love this technique, but I think it's sufficiently repeatable, and consistency from one part to the next is the most important factor here.

From there, it's a pretty quick matter of (long) center drill, (long) drill and ream 0.251. The Noga backside countersink tool comes in handy again here.

Rim Segment End Faces

And now, the fixture gets to do its job! I ended up burping out the lower fixture hole to .253 for just a touch more clearance, and the fit between the setup part and the fixture is tappy-tap snug, but everything goes together nicely and results in a decently rigid setup. The assembly goes in the vise and makes for quite a stack - it's a good thing my mill has a riser block for jobs like this one. The carbide roughing end mill comes out again, and the first face is machined. But to what dimension? Because the bolt hole is a known distance from the end of the fixture, the end of the fixture is used as a reference for where the end face of the part needs to be. In this case, a depth mic can be used to measure from the face being machined down to the fixture, with the target dimension being 0.200".

There was a hint of vibration here and there, but really everything performed very nicely. About 10 thou of stock is left for grinding. I couldn't resist an early fit check against a 3d printed part, and the results are very encouraging! The machining allowance I put on these castings is turning out to be quite excessive, but I'd much rather have it and not need it than the alternative.

Oh and a bonus - the hub/spokes assembly is now vertical, and lives on a temporary shaft on some roller stands - partially because I had nowhere else to put it, partially for giggles to see it spin.

Fantastic work 

More extraordinary model engineering going on with the massive flywheel, and at a physical scale that takes the work well outside the realm of what most modellers are familiar with in home workshop.  This is a remarkable project.  Can't say I much fancy sawing up 2" thick steel plate to make a jig  ( or to make anything!)  Dave