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

[bananarchy]

Introduction

Here begins what will be a very long and daftly ambitious undertaking, but something that, when reduced to its individual elements, at least appears to be feasible. Some years ago, I happened across mention of this engine in Wonders of Machinery Hall, an account of one of the main exhibits of the 1893 World's Columbian Exhibition in Chicago. There was all manner of fascinating engines and manufacturing equipment, but one in particular stood out. This was purported to be the largest mill-style engine ever built, at least at the time, and was used to drive dynamos and generate electricity for the fair. The cylinders measured 26", 40", 60" and 70" with a 72" stroke, and the engine ran at 60rpm.

Even more interesting than the quadruple-expansion setup and the massive scale of the engine, though, was the valve mechanism. I managed to find an original copy of an arrangement drawing from a period publication, and noticed that in addition to the regular eccentric which drives the wrist plate as usual, there is a second, smaller one which feeds into the governor linkage somehow. Strange! More detail about that in a subsequent post, as it needs a bit of a treatise all on its own.

Over the course of the last couple years, I got involved with an organization that has iron foundry capabilities, plus some machine tools, and I also managed to acquire and set up a machine shop of my own (something I've been fantasizing about since I was a teenager). I had started modeling the engine in solidworks, partly for giggles and partly to try and reverse engineer the valve mechanism. A few months back, I realized I actually had all the resources and capabilities necessary to take a stab at really making this thing.

[bananarchy]

The Miniature

So if we're going to build it, the next question is, how big? The answer, effectively, is as big as possible. I just like big engines to begin with, but additional scale also allows things to run more slowly and more smoothly, and be able to do real work. Also, one of the most interesting aspects of this engine is the trip gear and all the associated fiddly little linkages. I would like those parts to be scaled to the rest of the engine as closely to real practice as possible, and making everything bigger makes those parts more practical. The big parts can't be too big, though.

The determining factor ends up being the flywheel - this will be made as an assembly of castings, just like the real one, and it must be turned as a finished assembly. I have access to an Axelson lathe with a maximum swing of 30 inches, and the flywheel on the original was 30 feet in diameter, so bam. 1 inch to the foot. Perfect. At that scale, the trip gear parts are small, but totally doable, and a good bit bigger than plenty of things I've worked with professionally (I design robotic surgical instruments).

The engine will drive two dynamos with two concentric belts, which will allow load to be put on the engine to demonstrate the operation of the governor and trip gear under varying loads, and allow the compounding to properly work (or as much as it can without the vacuum from a condenser). Including the dynamos, the model will be about ten feet long, and the cylinders are 2.125", 3.3", 5.0" and 5.8" with a 6" stroke. The flywheel will be 30" in diameter and 6" wide on a 1.75" diameter crankshaft, and will weigh a bit under 200 pounds when finished.

The large bits are pretty much sorted, design-wise. There's still a fair bit of detailed design work to be done on the trip gear, and the governor will be a whole project in itself. The flywheel, though, is straightforward to design, and is a nice self-contained project, so that's where I'm going to start.

[peatoluser]

Looking forward to following this build.
I notice the drawing is from 'The Engineer'. By chance I have a pdf from the rival periodical 'Engineering' that covers the same engine and you're right, from the description, it is a complicated valve arrangement!   
Good luck with the build

[crueby]

Looks like an excellent engine to model!  Will be watching along...   

[Sanjay F]

Wow - what a feat of engineering the original is and so too will be the model. 30" flywheel, that's going to be something to behold!

Very best of luck with it and I'll be following along intently! 

[crueby]

Yes! It hadn't really sunk in how BIG this will be, it will definitely be able to do some real work!

[CI]

A twin tandem; very interesting project !
Typically the second eccentric controlled cutoff, and the first eccentric was for admission; at least that is my guess.
Corliss valve gear can get extremely complicated, such as compounding the action of two eccentrics to give a variable cutoff.

I like larger scale model builds, for the same reason as this poster, because the small parts and fasteners are very difficult to make when the scale gets small.

If you intend to cast the parts, keep in mind draft angles and machining allowances, and a shrinkage factor.

While this will be a very large engine, I don't think it is too large, but you definitely will not be carrying it out and putting it in the car.

Great subject for a build.
Good luck.


.

[Jasonb]

It's a big project for sure.

You mention your design background but have you done much machining in the past?. Also do you plan a large steam boiler to run this from as air won't work well with the compounding and would need an equally large compressor.

[Kim]

Looks like a very interesting project.  And quite big!  I assume you won't be moving it around much? 

Will be following along.
Kim 

[bananarchy]

Transport wise, I'm figuring the engine will be built on top of a table-height steel frame with some beefy casters on the bottom to facilitate moving it around, but transport is definitely going to be a trailer job. Boiler wise, the organization I'm with has multiple boilers of varying sizes that we take to shows and events, so thankfully that's not a worry. This is my first foray into designing castings, but I've spent a good while in machine shops. Some of the work will definitely be stretching my skillset, but hey, that's part of the fun!

[bananarchy]

First Part: The Flywheel Hub

The flywheel is to be constructed in a fashion as close to the original as possible (which is pretty much the easiest way to do it anyway). It is an assembly of the hub, 12 spokes and 12 rim segments bolted together. The original hub was split down the middle, but I've elected to make it a single part for the sake of simplicity and strength. This could have been done as an iron casting, but given that basically every surface would need to be machined in order to make things run true, and with the extra effort of making a pattern, I decided to machine it from steel. This was also helped by a fortuitous find at the local steel yard. The flywheel hub finishes at 7" in diameter and 3.5" wide, and I found a hunk of steel round bar in a corner that was 7.5" in diameter and 3.8" or so long. Perfect! This lump is 47 pounds to start, and the finished part will be about 15 according to the cad model.

My machining workflow on this ended up being pretty complex, and probably moreso than really necessary. This is largely due to the fact that the big lathe I have access to (30x120 Axelson) is a bit iffy in the precision department (or so I thought when I started) and I wanted to do all the precision finish machining on my Hardinge, which does not have nearly enough chooch to do the rough machining on a part this size. Since I didn't trust the big lathe to cut the bore as straight as I wanted, the first step was boring the 1.75" center hole on the mill. A long and slow process, since the length of the boring bar means a very low RPM to yield a good surface finish, but I was happy with the result.

Once I had my finished bore diameter (a few tenths under the nominal), I went ahead and turned a mandrel that will be used for the majority of the machining. The initial roughing and grooving is done with the part in the chuck in the Axelson to maximize rigidity, but everything else will have the part held on the mandrel shaft. This made use of the custom steady rest I made for the Hardinge, which was the first real project in the new shop earlier this year. I managed a nice snug fit on the diameter, about 0.0005" clearance.

That done, the part is moved to the big lathe (which makes even pretty decent sized parts look tiny). The mandrel was slid into the part for the purposes of indicating, and jacking bolts were placed between the backside of the part and the chuck to make getting the bore axis running true easier. I'm leaving a healthy finishing allowance during the roughing, so this doesn't have to be dead nuts.

Next: Time to make some real chips!

[bananarchy]

Flywheel Hub: Heavy Turning

This setup was chosen to provide maximum rigidity for as much of the material removal as possible. The rough machining of the outer faces is pretty straightforward - I've got some nice carbide 1" shank lathe tools which made quick work of skimming down the OD and the face, then facing down the outside features, leaving 0.050" on every face for finishing in the Hardinge (this turned out to be much more than necessary, but better safe). I was running the lathe somewhere in the 200s RPM for this part.

The real kicker on this part, though, is the central groove. It is 1" wide and nearly 2" deep radially, and it needs to have a flat bottom. This wasn't remotely feasible with the carbide I have on hand, so I tracked down a king-size candy bar of high speed steel - 3/4" wide and I think 1" high. It even already had a pretty close grind to what I needed, I just did a bit of cleanup and added some relief here and there. This looks right at home in the E size Aloris tool holder - those things are no joke!

RPM was reduced to 59 (speeds available on this lathe run from a max of 555rpm to a minimum of either 6 or 9rpm, can't remember) for the high speed steel, and the grooving tool was just plunged right in there, hand fed. This is easily the heftiest cut I've ever done, but the lathe never blinked and it worked wonderfully. Quiet, smooth, good surface finish, not a hint of chatter anywhere. This is where having a big, heavy, rigid as hell machine makes a big difference. You know you're doing something serious when the swarf makes a solid *thonk* when it hits the chip pan.

[crueby]

That done, the part is moved to the big lathe (which makes even pretty decent sized parts look tiny).

That lathe makes my LATHE look tiny!  Great start!

[bananarchy]

Flywheel Hub - Finish Machining

Once the big groove was roughed out, the first keyway was broached in the hub to allow it to be driven on the mandrel (plus a 7/16-20 set screw hole), and it was mounted in the big lathe to finish roughing the backside. After that, it goes into the Hardinge for finish machining. This ended up being a bit of a puzzle to figure out combinations of tools/holders/compound positions etc to be able to machine all the necessary surfaces, especially in the groove. I had 3d printed the finished part previously just for giggles, but this actually ended up being really helpful - I just put the 3d printed part in the toolmaker's lathe before I even started the part in order to make sure it was feasible. I was a bit concerned with the tool stickout, but I ended up finishing the groove width out to 1.001" with a taper of a couple tenths from top to bottom. Good enough!

One turning feature remains - the radius between the inner and outer ring of fasteners on the hub. This was also too beefy of a cut for the hardinge, so back into the big lathe with a hand ground tool (using a 3D printed radius gauge) to finish out the turning. The surface finish wasn't quiiite what I was looking for initially, but a bit of sanding and scotchbrite took care of it.

Next up: MANY HOLES

[bananarchy]

Flywheel Hub - Bolt Holes

The last big step on the hub is the addition of the bolt holes - each spoke is affixed to the hub with three 1/4" studs, so that's 72 holes in total, in two rings. These are all drilled from one side to ensure alignment, and reamed 0.251 to keep everything nice and snug. The initial setup is slightly ticklish, as the bolt holes actually require specific clocking relative to the keyway. The idea is that the keyway is lined up with the plane of the joint between two spokes, and a small semicircular channel is milled in each spoke to allow an allen wrench to sneak in and get to each of the two set screws (these two set screws will be the only OTS components in the flywheel). A piece of keystock was placed in the keyway, and I indicated a parallel clamped to the keystock to clock the keystock with the Y axis of the mill to provide that angular reference (with the rotary table set to 15 degrees, so that the bolt holes and spoke centerlines land on 0, 30, 60, etc).

Each hole was center drilled, drilled, reamed, and countersunk. The bottom side holes were also centerdrilled before drilling to ensure accuracy, which required an extended centerdrill. This was several hours of rotary table cranking, but everything turned out great. To deburr the holes on the inside of the slot, I got a Noga reversible countersink tool that worked like an absolute champ - this would have been a nightmare otherwise, especially with the inner ring of holes. And that's a (virtually) done part! The second keyway gets broached and gets its setscrew, then this one is finished. Oh look, that's a fastener! More on those soon.

[Michael S.]

The component is larger than I first thought. The disc says 1 1/2 inches, and for us, 1 = one. But it's definitely seven and a half inches!
Great work.

Michael

[Chipswitheverything]

A very impressive start has been made on this formidable engine project, which in engineering terms is rather like the sort of massive model engineering usually associated with one third, or even half size, traction engines and road locomotives!  Looking forward to seeing more details of your build of this mighty steam engine as time goes on.  Dave

[bananarchy]

Flywheel Spokes - Casting Time!

One of the key factors that makes this project remotely doable is the fact that my machine shop shares space with an (amateur) iron foundry. I'd never done any pattern making or casting prior to this, so some learning curve is to be expected. The advent of 3d printing also makes this SO much easier - the ability to simply 3D print one's patterns instead of crafting things by hand is also critical to being able to make accurate parts in a timely manner. A bit of bondo and filler primer is required to smooth things out

The design and geometry of the flywheel rim segments make that pattern significantly more complex, so I started out with the much simpler flywheel spokes. The first pattern was for a single spoke, angled to fit within our most common size of casting flask. This is rammed up, and the sprue is cut by hand into the upper part of the mold for the molten iron to be poured into. The first casting turned out beautifully! Good fill, negligible shrinkage, and great surface finish. In my excitement to start machining it, I clamped it to the mill table a bit too enthusiastically and promptly broke the casting. The pattern also got broken when trying to make a second mold, due to too much air pressure in the mold squeezer. WELP. A two-cavity mold will be more efficient anyway. On to version two!

The geometry for the two-up pattern was basically unchanged, and required the use of a longer flask. The sprue goes into the runner between the two parts. The P shaped geometry is a spin trap, which is intended to fill up first and catch any loose sand or debris before the part starts to fill. Two molds were rammed and poured - the first pair had some shrinkage, so the second had risers cut into the mold. These are larger volumes of metal above the part which are intended to solidify last, and contribute material to the part as it cools and solidifies to minimize sinks and voids. Four parts!

Time for some test machining!

[bananarchy]

Flywheel Spoke - test part machining

The spoke with the worst sinks was selected as the setup part to prove out the design and machining workflow. This consists of first milling and then grinding the ends to the correct thickness to interface with the hub and rim segments, drilling the bolt holes, and then milling the exterior sides of the ends.

For the milling, the part is clamped to the mill table with two clamps across the spoke snugged down only lightly to keep it from flying off. Additional constraint is provided by toe clamps against the outside to prevent movement on the table. The machining allowances are pretty generous, since I found out rapidly that light cuts on the skins of the casting were quite unkind to the milling cutters. Both ends are milled and ground to the finished dimension of the root (1 inch) and then the head is milled and ground further to its dimension (0.750).

I realized somewhere in this process that I'd made a bit of an error in the spoke design/pattern: effectively, the head of the spoke is too big in a couple of dimensions. When getting it down to thickness, the machined area extends too far down the spoke towards the center of the flywheel, leading to the machined area extending beyond the interface with the rim segment, and being visible. This is actually the case with the root as well - the parts ended up slightly thicker than intended, and the large radius fillets leading to the pads at the ends make this a really sensitive dimension. I finished out the machining in order to learn what I could, but we're gonna need to alter the pattern and make more parts to address this.

On to drilling! Now we've got to start paying attention - how do we locate the bolt holes relative to the casting? A guide was 3D printed to show the hole locations and the finished outer dimensions of the spoke pads (as well as the surfaces where the hub and rim segments stop). After the centerlines of the spoke ends were squared up to the mill, the positioning guide is positioned and then a center punch marks the inner bolt hole. Pick up on the hole with a wiggler, then drill and ream all holes 0.251.

I whipped up an aluminum fixture plate to aid in the milling operation - since we want to locate the milled features relative to the bolt holes, this allows the part to be bolted down parallel to the X axis for the straight cuts and at an angle for the angled faces, and the cutting is done at known locations relative to the bottom right corner of the fixture plate. Shoulder screws are used in two of the holes to provide accurate location, with regular 1/4-20s in the rest of the holes for additional securement.

[CI]

Nice pattern and casting work !
Great surface finish.
Rather convenient to have an iron foundry on hand; don't see many of those.
Watching with much interest.
 

[bananarchy]

Flywheel Spoke - Test Part Cont.

The part is test fit with the completed flywheel hub. When grinding the spoke root thickness, I ended up with about .0005" clearance in the hub slot. Tighter than it probably needs to be, but very nice to feel when assembling. With the bolt holes reamed .251 in both parts, 1/4" fasteners go through the holes readily. The material for the studs I will make is about .250 on the nose, so I'll probably ream most of the holes in the final spokes .253 to give things a little more wiggle room, but it's pleasing to know that my hole locations and the squareness of the assembly are that accurate.

In the last photo, the spoke is joined with a 3d printed flywheel rim segment, and we can see that the machined face of the spoke head extends beyond where it interfaces with the rim. This is exaggerated in this instance because I intentionally biased the location fixture to make the hub interface line up where I wanted it on the casting, rather than splitting the difference. Still though, the spoke shaft needs to be thinner and the fillets need to be altered. New pattern time.

[bananarchy]

Flywheel Rim Segment

This component is a greater challenge than the flywheel spoke - owing to the angle of the ends and the shape of the interior geometry, it cannot be made with a simple two-part mold. Instead, a core, or a sand structure which is formed separately from the main mold and assembled with it, is used to form the part geometry which would otherwise be an overhang. The core is made by ramming sand into a 3D printed corebox, which another little design puzzle in itself. This whole pattern designing endeavor was a serious spatial-reasoning head-scratcher at multiple levels of remove, but I feel like I came up with a decent solution.

The second picture shows the as-cast part. The red surfaces of the part are formed by the pattern, and the grey surfaces are made by the core. The third is the pattern itself - the black part forms a hole in the mold for the core to drop into.

Next we have the 3D printed and finished casting pattern followed by the corebox, which is a 4 piece assembly.

Time to ram up a mold! Unlike the spokes, the pattern is not mirrored on both sides of the match board - the other mold half is just flat except for the sprue. Next the corebox is rammed with sand and leveled (one of the inputs to core design is that it must have one flat face which is the open side of the box). The box is then disassembled very gingerly.

[bananarchy]

Flywheel Rim Segment Casting

I fiddled around with different methods and sequences of disassembling the corebox to best preserve the core - the sand is pretty delicate, and I understand that often additional binders are used in the sand in these applications to aid handling. Something to look into.

The cores are assembled to the mold - one fell to bits on assembly, so I started over and rammed up a second one. Bit of tearout on one exterior corner, but whatever, that surface of the part is getting machined. It was poured (I was actually on one end of the crucible for this one) and the results were.....fantastic! Basically zero issues. There is a tiny bit of flash where the metal got between the mold and the core, but it's extremely thin and very easily snapped off. No sinks, great surface finish. Could not be more pleased.

[bananarchy]

Flywheel Rim Segment Casting

After only some very minor fettling (and significant fondling), the part is looking fantastic - now to repeat the process 11 more times (plus a spare or two). Making the outer surface of the part flat instead of rounded might help make the machining process easier? It will get turned as an assembly of course, but that's a lot of extra material to remove in an interrupted cut. Not convinced future-me is going to be happy with this decision, but time will tell. The next big task is going to be figuring out the machining process - locating the machined geometry relative to the cast features on this part is pretty ticklish. The cast surfaces must line up nicely with the adjacent parts, and there are a lot of ways this can be wrong. Once that's done and datums are established, the rest isn't too bad, but I haven't figured out quite how to go about it yet.

[CI]

Great pattern making/mold making/casting work !
Awesome for sure.

"LinoCure" (tm) by Ask Chemical is a resin binder that is good for use with cores, and/or the entire mold.
Has to be used with very dry sand such as OK85.
Designed for use with iron and steel.
And you can spray on a ceramic mold coat such as "Velacote" (tm), also by Ask Chemical, for a beter surface finish.
Resin-bound cores and molds are very strong, and you can vary the set time by varying the catalyst amount.
Available in 5 gallon quantities.
Sand is not easily reused.
If you have a non-critical flat surface that has little or no draft angle, you can cut a piece of mylar film, and cover the surface with it, which prevents the sand from sticking to the surface.

.

[Jasonb]

The initial castings have come out very well

Can I ask what printer/filament combination you are using and also what surface prep you are doing to the pattern as I can only see the tell tail printer layers on surfaces that won't matter?

[bananarchy]

So slight spoilers, I've actually just printed version 4 of the spoke pattern due to some minor issues with V3. The first three were done on a Flashforge, which I was fighting constantly and which did not have a big enough bed to print the whole spoke in one part. Having to split it up led to inaccuracies and a lot more finishing work. I've been using automotive body filler to smooth out the big stuff, and automotive build primer, with a polyurethane gloss coat on top.

Recently though I pulled the trigger on a Bambu H2S, after having great experiences at work with their X1C, and it's been fantastic. Total game changer. The bigger work area allows it to do the spoke in one go, it's way faster, and the quality is top notch. These were printed on the max quality settings in the basic PLA, and I haven't started the finishing process yet but I expect it to be a whole lot less work than previously.

[Jasonb]

Thanks for the details, latest prints look good.

[bananarchy]

More Spokes

After machining the test part, adjustments were made to the design and a third (and then fourth) version of the pattern were made. Number 3 made good parts, but I was having significant trouble getting the mold to separate correctly - the bit of sand between the spoke roots kept sticking to the pattern, due to it being too small of an area that was trapped on most sides by the pattern itself. For version 4 I flipped the spin traps around and moved the spokes farther apart, and this did the trick. I used some freshly mixed sand for the last two pours and the surface finish is the best I've seen yet. I'm still getting a bit of porosity in the root sometimes - the lesson seems to be that the riser always needs to be bigger than you think. The last couple pours ended up a bit short on material, but when properly filled it seems to turn out great. I'm up to six good parts now (plus one that ended up with a big inclusion at the root). Halfway there!

[steamer]

Watching along!

Dave

[Dave Otto]

Nice results!

Dave

[bananarchy]

Flywheel Spoke Machining - End Faces

After a few more pours, I've got fourteen (potentially) good parts and two setup parts ready to go on the mill. A couple will end up having more shrinkage porosity than I thought, so I'll have to cast a couple more, but I'm proceeding with this set for now, since it's going to be a bit before the next pour.

The mating ends of the raw castings are about 1.400" thick, and the objective is to finish the hub end at 1.000" and the rim end at .750", with the cast shaft of the spoke located symmetrically between the machined end faces. To achieve this, each spoke ended up going on the mill table 7 times and the surface grinder 4 times. There was probably a way to reduce that count slightly, but results matter more than efficiency in this case. Both sides of both ends were roughed down leaving .050" per side, and then measurements were taken on the surface plate to see how asymmetrical the shaft was to the rough faces. The shafts are rounded and tapered, so a consistent location was marked from each end, and the measurements in this spot were compared when the part was flipped over. Each part was marked with the necessary adjustments, and material was removed as needed from each end, with shims placed as needed under one end on the second cut to ensure everything is properly parallel. Some parts required no adjustment at all, and the worst was about .035" out. Not bad.

Following centralization, the ends are brought down to the final (mill) dimension, leaving 5 thou per side for grinding. Clamping these on the table was a little tricky - I've got the aluminum bars running across the spoke shafts, but any real force on these bends the shafts and distorts the geometry of the ends, so the main constraint is with toe clamps from the sides. Not my favorite, but nothing moved.

Both sides (and both ends) are then ground to 1.001" for a nice snug fit with the hub (the width of the mating groove ended up a grand or two above nominal). Four parts fit nicely on the 8x18" mag chuck.

[bananarchy]

Flywheel Spokes - End Faces Cont

Now with both ends at 1.0", only four steps left - mill, grind, mill, grind on the rim ends of the spokes to get them to .750". The first side repeats the previous milling setup, with 5 thou left for grinding (to a total thickness of .875"). For the second side, a spacer is required between the spoke end and the table, so an old parallel was sacrificed to the gods of precision and ground to .1255" (the extra half thou is there because the hub ends are actually 1.001"). After one last trip to the mill, the final side is ground in batches of 3. This is the first real job I've done with this grinder and I'm still learning a bit, but having the right wheel definitely makes a big difference (Norton 32A46-IVBE). I was able to hit the thickness +/-.0002" no problem, with most of the parts within .0001". Grinding really helps with getting everything nicely flat and parallel, since there's basically zero distortion due to workholding forces.

Next up, drilling a bunch of holes!

[CI]

The castings look very good.
A few thoughts about risers, runners, gates, sprues, etc.:
I can only speculate; I don't know exactly what would or would not work in your exact situation, so take all this as what if's.

1. I normally use a rectangular gate at the top of the runner, so the runner would be in the drag, and the gate in the cope.
The idea is that when you pour, the runner fills first, and sweeps slag, inclusions, loose sand, entrained air, etc. into the spin trap before the metal completely fills the runner.
Once the runner is full of hot clean metal, then the gate starts filling the mold cavity.
If the runner and gate are at the same level, some trash will get swept into the gate as the initial metal flows past the gate.

2.  You could use a sprue at one side where one of the spin traps is located, and let the runner feed a single spin trap on the opposite end of the runner.
This would allow you to use one spin trap only, and stil get the sweeping/cleaning action.

3. The abrupt 90 degree transition at the bottom of the sprue where it meets the runner will cause a splash back when the sprue is filling, entraining air, slag, etc.
The bottom of the sprue could have a smooth radius transition into the runner to maintain laminar flow.
The spin trap will take care of the initial turbulence and entrained air/sand/slag, but the turbulence during due to a 90 degree bend may break off some sand.

4. Risers are always a bit of an art.
If I were doing it, I would have a 2.5" diameter, 4" tall riser above each end of each spoke, with a neck at the base of the riser into the casting about 1" diameter.
Risers tend to push the crucible size up quite a bit.
Having large sections on either end of a smaller section would be prone to hot tears without risers.

I have seen some use a runner down the center of two long castings, with gates branching off to the mold cavities in two or more places, with the sprue in the center of the length of the runner.
Again, I would put the runner in the drag, and the gates in the cope at the top of the runner.

Your castings are so good that one can only speculate on possible ways that may or may not help to improve them.
Looking great !
Following along.
 

[bananarchy]

Flywheel Spoke Drilling - Initial Attempt

As with any castings, correctly positioning the machined geometry relative to the casting is a critical and potentially challenging step in the process. The first couple attempts didn't quite turn out right, as the geometric interactions between the components are kinda tricky, and getting everything to line up visually with the adjacent spoke in the hub was harder than I initially anticipated. A good bit of time was spent recently on other projects, but also just thinking about the location methodology and waiting until I came up with a method I could be confident would produce the results I wanted.

In addition to printing casting patterns, this is another part of this project where 3D printing comes in extremely handy. I'm able to model locating jigs which directly reference the cad model of the part itself, and iterate on the design with minimal expenditure of time and material. The basic idea of these jigs is to determine the location of the origin hole (the centermost hub bolt hole), which fully locates everything when combined with the part centerline. The initial attempt, done on a set of four test parts, relied on manually finding the centerline and eyeballing the longitudinal position to split the difference where the edges of the spoke pads interact with the hub and rim sections.

Once the centerline was scribed and the origin hole is center punched, the part is located in the mill using a wiggler and the holes are drilled and reamed. Next, the part is bolted to a fixture plate to machine the faces of the end for clearance. This worked nicely, since it only requires locating one corner of the fixture plate and machining to a known location.

It turns out that the eyeballing method wasn't reliable enough, and the alignment between adjacent parts wasn't fantastic.

[bananarchy]

Spoke Drilling - Final Execution

A secondary learning from the initial batch of parts is that there was a bit more variability than I like in the center to center distance of the bolt holes at the outer ends from one spoke to the next - this makes sense when you think about it, since any small variance in the hole locations at the hub end is magnified ~10 fold at the outer end. New plan - drill the outer holes on the rotary table as an assembly.

The locating fixture was updated to reference more geometry and take the eyeballing out of the equation. Pins were added to reference the pad edges to ensure a consistent cap to the edge of the hub, and a slider was added to reference the outer edges of the spoke shaft. Finding the middle of the spoke shaft was tricky due to the taper and casting variance, but this worked like a champ.

The full batch of parts was drilled, reamed and milled for clearance as above. I got a 5/8" carbide roughing mill recently and it will take some monstrous cuts in cast iron without the machine complaining at all - strong recommend. Then everything is test fit in the hub for the first time (just last night!). I've cut the stock for the studs to length, so it's the final material and size just without threads yet. Most went together with no effort or a light tap, one has alignment issues but given how tight the clearances are that's not bad at all. I'm extremely pleased with how the adjacent parts line up at the hub interfaces.

[bananarchy]

Spoke Drilling - Results

Here's the final assembly, and also a look at how it will interface with the rim segments on the test parts which had the rim holes drilled

[crueby]

Thats quite an assembly, the wheel parts look amazing!   

[Sanjay F]

Wow!! 

[bananarchy]

Flywheel Rim Segment Casting

After proving out the pattern and corebox strategy, a second version of the pattern was made that eliminates some of the extra material on the exterior face - there's still a flat on the part which will be convenient for machining, but there's less extra to have to turn off the OD, and the final surface will be closer to the cast surface of the part, minimizing the risk of encountering porosity on the OD face of the finished part. A sizable riser was also added. One initial test part was done which ended up with some gnarly inclusions, and then a batch of four proper parts was poured. Pretty happy with the results - #3 had something funky happen on one corner, which might or might not clean up, and there's a wee bit of shrinkage porosity in the riser neck on one or two parts. Dimensionally we're in good shape, and I'm very pleased with the surface finish.

[bananarchy]

Flywheel Rim - Orientation and Reference Face Grinding

The locating and machining sequence of these parts has been quite the puzzle - there aren't nice reference surfaces on the part itself, everything is angled, etc. The most important parameter, though, is that each segment lines up nicely with its neighbor at the end face where they bolt together. So that is what we need to locate the part relative to, but how? I designed and 3D printed a nest which cradles the part at four points of contact, which are the outermost corners of the faces I want to line up. The nest is in two parts which slide together, both to accommodate for part to part variation but also to allow the nest to make it past the overhang. When placed in the nest, the part is located in two degrees of freedom.

Now that we've got it located, the reference surface flat is machined in the surface grinder - this is a very time consuming process, but minimal cutting forces are necessary given the less than ideal workholding setup, and since the grinder is automatic it's not too bad. The nest includes a pocket in the center for some metal to help hold it on the mag chuck, which incidentally didn't work at all  so the part was blocked in thoroughly. This worked pretty well! The part was ground until the face cleaned up basically all the way across, rather than to a specific dimension.

To check the orientation of the setup part, lines were scribed based on the edges of the nest (which are close to the finished end faces post machining) and the height of those points was compared on the surface plate - ended up within a few thou! More than good enough.

 Next, that face can be clamped to a right angle plate and then one outer edge of the part skimmed to orient the part in the next DOF

[cnr6400]

 

[Chipswitheverything]

What 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

[pgp001]

That flywheel makes mine look like a baby at only a foot diameter.

[CI]

I 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 !

.

[bananarchy]

What 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.

That 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.

I 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 !

.

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