Stuart 5a stationay build

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Bob Sorenson

Well-Known Member
Dec 21, 2022
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Harrisburg, SD 57032, USA
This project is the Stuart Turner #5a stationary steam engine from a casting kit. The 5a is the largest single cylinder kit in the Stuart line (Stuart Models | Steam Engines | Model Engineering | Executive Toys). It has a 2.25” bore, 2” stroke and 7.5” diameter flywheel. Here is a fine example of the 5a.


I plan on adding the Stevenson reverse mechanism, as shown above and a mechanical lubricator. Might add a second lubricator for the main bearings and trunk guide, we’ll see. At the time of this writing, the rotating assembly is done, and it turns great. ()

Unlike other Stuart kits, the 5a kit is castings only. There are no other materials, fasteners, or supplies. The threaded parts are all British standard, mostly 1/4” BSF and 2 British Association (BA). Since there are no fasteners, I decided to go with the Unified Thread Standard equivalent, which is ¼ x 28 and #10 x 32. The casting kit comes with a set of plans. The plans are a (probably 1/3) reduced photocopy of the old school vellum blueprints. They are mostly legible.

Get started with the base casting. Start off by trimming up the bottom to clean metal. Don’t take too much off, there is not a lot of height “meat” on this part. Be sure the 7.5” flywheel has room to turn. There was some “chill” on this bottom edge, however, a carbide cutter went thru it.

Base 1.jpg

Use a 1” diameter pin to probe the corners and the mounting lugs. Tap the casting around until centered.

Base 2.jpg

The base casting is not shown in the plans. Match the hold down bolt pattern from the sole plate. Tap with ¼ x 28.

Base 3.jpg

The mounting lugs turned out to be 7-7/8” apart. At first, I drilled for ¼” hold down bolts. Later expanded to 5/16”. Mill off the mounting lugs to about ½” thickness and deck off the base to clean metal.

Base 4.jpg

Enough for today. Next time starts on the sole plate.
Hey Bob, I am a big fan of the Stuart line, and am a huge fan of steam engines with a 2.0" (+) bore !

It is vastly easier for me to machine and see larger cast parts.

Wow, your flywheel and crank assembly spins like a top, with no flywheel wobble.
An impressive feat for sure for many to get those parts exactly right.

I am glad Stuart is still producing engines.
That is an iconic line of engines for sure.

I look forward to your build.

Pat J
Next up is the sole plate. Mill to clean up the bottom edge of the casting. Then, using a 5/8” or ½” pin probe all the corners and hold down bolt pads. Center up the casting as best as possible. Once centered, zero out the DRO or dials on the mill.

Sole Plate 2.jpg

Run around the inside of the sole plate opening to clean it up. Mill the inner cheeks of the bearing pockets to the final inside width.

Sole Plate 3.jpg

Mill the outer cheeks of the bearing pockets to final outside width.

Sole Plate 4.jpg

I’m not sure what these little tabs on the ends of the sole plate are for. They are on both ends. They might be a bracket to hang an accessory item. Anyway, mill them flat and they will be there if needed.

Sole Plate 5.jpg

Deck off the sole plate and mill slots for the bearing caps.

Sole Plate 6.jpg

The DRO makes this easy and very accurate. A 1-1/8” parallel dropped in perfectly.

Sole Plate 7.jpg

All the tapped holes in the sole plate are ¼ x 28.

Sole Plate 8.jpg

Next, rough out the bearing seats using a ¼” ball end mill. Using some shop math, calculate a table of X and Z axis values for the cutter. The final bearing diameter is 15/16”. Rough out to 7/8”.

Sole Plate 9.jpg

That’s enough for today, we’ll pick back up with more on the sole plate next time.
Back on the sole plate today. The plans call for a small pin at the bottom, center of the bearing pockets. This isa to prevent the main bearings from accidentally spinning in the sole plate. The plans don’t call for a specific size, so 1/8” diameter seems about right. Drill 5/16” deep.

Sole Plate 10.jpg

There was very bad sand inclusion on two of the bolt down pads. Too much to simply ignore.

Sole Plate 11.jpg

The best way to fix this is on the rotary table with a 1/8” diameter ball end mill.

Sole Plate 12.jpg

Go in with a pointed stone on a Dremel to clean up the milling marks.

Sole Plate 13.jpg

The Sole plate is nearly done. Next step is to bore out for the main bearings. But, to do that we need to make the bearing caps. Start those next time.

Take care, Bob
There was very bad sand inclusion on two of the bolt down pads. Too much to simply ignore.
As I pour my own iron castings it is VERY annoying when that happens to me because you can only see that problem when the casting is machined. When that happens that casting is rejected and a new one is poured.
I don't think those faults are what are called sand inclusions. They appear to have been caused by sand missing from the mould, either through inadequate ramming leaving voids, or the pattern not releasing properly and pulling some sand out with it.
Yeah, I think it's a broken off piece of the mold. It was an easy fortunately. There are a couple surface holes on the standard but won't affect anything. Stuart castings are great to machine.
Today starts the bearing caps for the crankshaft. The bearing caps are very rough castings.

Bearing Caps 1.jpg

After cleaning up with the belt sander, clamp in the mill vise with some plywood jaws and mill off one side.

Bearing Caps 2.jpg

Clamp the bearing cap directly to the milling table to mill the other side to final thickness.

Bearing Caps 3.jpg

Center and level the bearing caps in the mill vise as true as possible. Mill the bearing cap retention notches and rough out the bearing slot as done on the sole plate. Drill for the cap bolts as well.

Bearing Caps 5.jpg

Flip the bearing caps over and spot face for the cap bolts. The #5a plans do not specify any method for bearing lubrication, other than just drill an oil hole. Initially I tapped these with #10 x 32, but later widened them out to ¼ x 28. Eventually there will either be an oil cup or a fitting for an oil line.

Bearing Caps 4.jpg

The fit is very good. Probably, at this point, stamp numbers on the parts for each side. As assembly progresses, keep all the parts in the same keyed location.

Bearing Caps 6.jpg

Next time we’ll line bore for the main bearings.

Take care, Bob
Today we’ll finish the main bearing caps and the main bearings as well. The bearings caps are inline bored first before the main bearings are made. To start, mount the sole plate on an angle plate and adjust to plumb. Insert a 1-1/8” parallel into the bearing cap keeper slots. Use a dial indicator in the mill spindle to plumb the sole plate.

Bearing Caps 7.jpg

A six inch long parallel is really needed for this task. I don’t have that length, so things were harder than they needed to be. Once plumbed, establish the center of the crankshaft. A long parallel makes this easier. In my case, the “world’s most dangerous fly cutter” with the 0.100” tip fit between the bearing cap keeper slots.

Bearing Caps 8.jpg

Make a boring bar from some ¾” diameter round bar stock and a sharp broad nosed tool to bore for the main bearings. This worked our real well, even though the cutter needed manual adjustment. A boring head would be more precise, but mine only accepts 3/8” tooling. I was concerned that would be too flimsy, but in the end, this worked out just fine.

Bearing Caps 9.jpg

Now for the main bearings. The Stuart #5a casting kit comes with split sand castings in gunmetal for the main bearings. A while back I built the Stuart #4 and used the sand cast gunmetal bearings that came with the kit. Those castings are extremely soft and wore out almost immediately. Now I have to rebuild the lower end of that engine. So, I did not use the bearing castings that came with the kit. Nor did I use split bearings. To me split bearings are an unnecessary feature. Instead, I went with single bearings turned from 932 bearing bronze. Turning and boring the main bearings is straight forward.

Main Bearing 1.jpg

Leave the inside face of the main bearings slightly long, then trim to final width after fitting to the sole plate.

Main Bearing 2.jpg

The plans show a small pin in the center of the bearing slots on the sole plate. This must be to prevent the bearings from spinning. There is no detail on the pins size, so 1/8” diameter will probably do.

Main Bearing 3.jpg

That’s it for now. Next time, we’ll get started on the crankshaft.

Take care, Bob.
Stuart no longer offers cast or forged crankshaft blanks with their kits. They now specify that the builder fabricates the crankshaft by either the Loctite with pins method or by silver soldering. The #4 engine plan calls for Loctite and pins. That method works perfectly. The #1 plan says either method. The #5a plan does not specify a method. I contacted Andrew at Stuart on which method to use. Andrew said Stuart has a vendor that makes #5a cranks by silver soldering. So, I went that method.

The shaft part is stressproof steel, Alloy 1144 and 1018 for the webs. The 1144 came with a lot of heavy mill scale. Starting with a length of ¾” diameter, center drill both ends and turn the shaft to clean metal. Fabricate the webs and wrist pin to final dimensions.

Crankshaft 1.jpg

The recommendation for silver soldering clearance with 56% cadmium free is 0.0015”. The tolerance is actually a little more forgiving than that. The parts should fit together smoothly with no slop.

Crankshaft 2.jpg

The plans do not specify a way to lubricate the wrist pin. Two methods I found include drilling passages in the crankshaft to take oil from the main bearings. The other method is to drill an oil passage lengthwise thru the connecting rod and big end to take oil from the crosshead. I decided to take oil from the main bearings. Before silver soldering the crank, drill oil passages in the wrist pin. Drill all the way thru the wrist pin and tap both ends with #4 x 40. Drill cross wise all the way thru.

Crankshaft 3.jpg

Clean all the parts thoroughly, flux and silver solder together.

Crankshaft 4.jpg

Mount the crank blank in the lathe and turn the shaft ends to final dimension. The final diameter is about 0.002” under the main bearings. I missed a little bit on boring the main bearings, and had to turn the shafts to match the bearings.

Crankshaft 5.jpg

The shaft ends came out very well. The 1144 material is easy to machine and cleans up to a nice polish.

Crankshaft 6.jpg

The crankshaft “hotwash” (after action review) is very favorable. The soldering method is not difficult. I put solder in from the outside and let it wick in. Some solder flowed out on the wrist pin and required clean up with a safe edge file. Next time I will mill some slots on the shaft, put the solder on the inside and let it wick outwards. Originally, I wanted to use 12L14 for the shaft material, but my shop mentor was concerned about silver soldering with the lead in 12L14. I’ve never had trouble silver soldering 12L14 but decided to go with his recommendation.

Next time continues with the crankshaft.
The crankshaft is turning out very well. The 1144 alloy steel cuts and polishes great. So, a test fit in the bearings and it turns smooth.

Crankshaft 7.jpg

There are two methods to lubricate the crank pin. One method involves drilling the connecting rod all the way thru lengthwise and draw oil from the crosshead. The other method is drill passages in the crankshaft and draw oil from the main bearings. I decided to drill the crankshaft.

Crankshaft 8.jpg

There will be some thru holes to plug. Use some 4 x 40 model hex bolts for that.

Crankshaft 9.jpg

Saw out the middle part of the shaft. Saw the shaft, not the web.

Crankshaft 10.jpg

And mill the sides clean. Tap some 10 x 32 holes to attach the counterbalances later. Also mill a 1/8” wide slot for the flywheel key.

Crankshaft 11.jpg

Here it is all cleaned up. I’m very satisfied with how it turned out.

Crankshaft 12.jpg

Next time starts the counterbalance weights for the crank.

Take care, Bob
Hi Jojo, I agree, silver soldering the crank is the way to go. Thanks.

The Stuart 5a kit includes cast iron castings for the counterbalance weights. There is a small nub cast into the inner part of the rim. It’s visible in the photo. I am not sure what that nub is for. It is not shown on the plan and did not appear on other examples of the engine. So, I removed them.

Counterweight 1.jpg

First is to machine the counterbalance weights to their final thickness. That cast recess is the inside portion of the weight. Machine off excess material so that the inner part of the weight is same width as the crankshaft web. It worked out well on the table of the mill.

Counterweight 2.jpg

Mill the top surface next. About 1/8” of material comes off to center the cast inside portion of the weight. Next mill a slot 7/8” wide by 7/16” deep. The slot must snuggly fit the width of the crank web. The 7/16” depth ends up on center line with the crank shaft. Finally drill a rather close fitting 10 x 32 clearance hole all the way thru. This is for attaching the weight to the crankshaft later.

Counterweight 3.jpg

Make a filler piece, 7/8” square, 7/16” thick with a small center drilled exactly center. Use thin CA glue (super glue) to glue the filler piece and weight halves together.

Counterweight 4.jpg

On the lathe, chuck a piece of surplus stock, face cleanly and cut some slight indentations with a “V” tool. This stock happens to be some 2-1/2” dia steel from the drop drawer, but any material will work.

Counterweight 4-1.jpg

Use CA glue again to fix the counter weigh assembly to the fixture. Use the center on the tailstock to align the assembly on the center of the filler piece.

Counterweight 5.jpg

CA glue is very strong, but not quite strong enough. Not shown in the picture is a ¼” thick piece of steel pressing against the counterweights by means of the tailstock. The CA glue coupled with a pressure plate will hold the work piece securely to finish the outer rim in one setup. When the counterweights are finished, break the CA glue bond with a small torch. CA glue yields at about 200F. Remove residue glue by soaking the parts in acetone.

The idea of using CA glue comes from Chris at Clickspring. He uses the method frequently to make clock gears. The method works great but be careful with generating too much heat. I’ve turned copper end plates for small boilers this way and it works fine. Just use a pressure pad, take light cuts, and let it cool occasionally.

Next time we’ll finish the counterweights.

Take care, Bob
Picking back up on the counterweights today and finishing up the crankshaft. CA glue holds the counterweights to a flat faced jig for turning round. CA glue is strong but is vulnerable to heat. So, use a piece of ¼” steel plate to provide some pressure to the set up.

Counterweight 6.jpg

The Stuart drawings don’t say much about attaching the counterweights. Use 10 x 32 machine screws to attach them. Countersink only slightly to ensure the screw slot is proud of the rim.

Counterweight 7.jpg

Grind off most of the screw head and firmly peen the remaining head into the counter sunk hole. Chuck the crankshaft in the lathe and turn off the remaining screwhead. While in there, chamfer all the sharp edges.

Counterweight 8.jpg

The rough castings had some round overs in the corners. The round over is shown on the plans. After the machine work, the round overs were either gone or different sizes. So, the put crank went back into the mill for some chamfers on the corners.

Counterweight 9.jpg

Tale of the tape. The “last word” said it was within 0.0015”.

Crankshaft 13.jpg

And the crank is all done. It turned out really well. The stressproof steel was easy to work and it polished up nicely. Silver solder built up was the way to go.

Crankshaft 14.jpg

Next time is the flywheel.

Take care, Bob
I turned the flywheel for this engine a few years ago. Then we moved, so the shop got packed up. Unfortunately, there are no pictures of the flywheel setup and rough turning. The process involved clamping the casting to the face plate with packing under the spokes to make some standoff. The casting was faced clean, bored, and reamed to 5/8” and the rim turned. All in one setup. Then the casting was reversed and faced clean. It was very straight forward job. The flywheel was turned on a Grizzly 9” x 19” lathe with plenty of room, power to spare and finished up fine.

As much as I tried to center the casting, it was lop sided. So, it went back into the lathe for some cosmetic work on the inner circumference.

Flywheel 1.jpg

With the inner rim and hub cleaned up on both sides, it looks a lot better.

Flywheel 2.jpg

The bore of the flywheel is broached 1/8”. I took it over to my shop mentor’s house to poke the keyway. He has a very precise press, much better than the Harbor Freight bottle jack press I have.

Next make the key using a little jig for the mill.

Flywheel 3.jpg

The jig pins are set for a 1:100 taper, with a stop pin as well. The jig with stock is clamped in the mill vice and worked a nice fit in the crank and flywheel. It’s a crappy picture. Just imagine the stock set at the correct taper and secured in the vice.

Flywheel 3.5.jpg

Finish the key to the standard dimension shown in The Machinist Handbook.

Flywheel 4.jpg

And with that, the rotating assembly is done.

Flywheel 5.jpg

Next time starts work on the trunk guide or standard.

Take care, Bob
Looking good! That key came out well.

The bore of the flywheel is broached 1/8”. I took it over to my shop mentor’s house to poke the keyway. He has a very precise press, much better than the Harbor Freight bottle jack press I have.

What I do when I broach a keyway with a bottle jack press is use the press and release method. Start broaching the keyway, release the pressure on the broach and then press again. Do that a few times until the broach is well seated in the bushing and you shouldn't have any problems.

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