Stuart Turner 5a Build

Where users can chronicle their builds. Start one thread and continue to add on to it.

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xo18thfa
Posts: 177
Joined: Tue May 17, 2005 11:59 pm
Location: Harrisburg, South Dakota

Re: Stuart Turner 5a Build

Post by xo18thfa »

The piston rod and crosshead are one single casting. As with many of the castings, this one is way oversized. The casting has a very nice profile, but it will all go away during machining. I’m not sure what Stuart uses for the connecting rod and the piston rod castings. It turns like some kind of steel, not quite as crumbly as regular cast iron. Whatever it is, it machines very well.
Piston Rod 1.jpg
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The method to use is straight turning between centers. Start by center drilling both ends.
Piston Rod 2.jpg
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Get it up between centers. I would say fabricate a driving dog specifically for this part.
Piston Rod 3.jpg
Piston Rod 3.jpg (258 KiB) Viewed 19921 times
Turn the shaft to final diameter and polish. Leave the very top end blank for the time being.
Piston Rod 4.jpg
Piston Rod 4.jpg (271.03 KiB) Viewed 19921 times
Turn the piston rod end for end and machine the crosshead.
Piston Rod 5.jpg
Piston Rod 5.jpg (312.79 KiB) Viewed 19921 times
Ultimately, the piston attached to the rod by means of a taper and nut. Don’t try to do the taper for the piston now. It’s a good idea to do the cylinder bottom cover first, then do a “sanity check” on the piston rod. So, hold off on that. Next time we’ll finish the piston rod on the crosshead end.

Take care, Bob.
Bob Sorenson, Harrisburg, South Dakota
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Harold_V
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Re: Stuart Turner 5a Build

Post by Harold_V »

xo18thfa wrote: Fri Jan 12, 2024 7:45 pm I’m not sure what Stuart uses for the connecting rod and the piston rod castings. It turns like some kind of steel, not quite as crumbly as regular cast iron. Whatever it is, it machines very well.
Assuming the chips in the picture are from the rod, it's most likely ductile iron. It machines much like gray iron, but, as you described, is more inclined to make chips that tend to not crumble quite as easily. It's a great choice as it offers ductility that isn't found in gray iron, yet is still an acceptable bearing, unlike steel.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
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xo18thfa
Posts: 177
Joined: Tue May 17, 2005 11:59 pm
Location: Harrisburg, South Dakota

Re: Stuart Turner 5a Build

Post by xo18thfa »

Hi Harold. That's what it must be. The chips from the rod have a bit of a curl. The other casting chips were dust and very messy.

Thanks, Bob
Bob Sorenson, Harrisburg, South Dakota
Andy R
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Joined: Wed Sep 26, 2007 2:18 pm
Location: So. Calif.

Re: Stuart Turner 5a Build

Post by Andy R »

Very nice work.
You are inspiring me to build another stationary engine ... as if there are not enough projects.
Again, very nice work
Regards,
Andy
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xo18thfa
Posts: 177
Joined: Tue May 17, 2005 11:59 pm
Location: Harrisburg, South Dakota

Re: Stuart Turner 5a Build

Post by xo18thfa »

Thanks Andy. Gotta get busy.

Next for the piston rod is get it between centers with the dividing head to shape the crosshead portion. Mill the crosshead to the final width on both sides.
Piston Rod 6.jpg
Piston Rod 6.jpg (271.84 KiB) Viewed 10598 times
All of the nice-looking cast features on the crosshead are gone. Start profiling those shapes back in. Work the lower end and side cheeks in the mill.
Piston Rod 7.jpg
Piston Rod 7.jpg (219.96 KiB) Viewed 10598 times
On the rotary table, carve out the wrist pin bosses.
Piston Rod 8.jpg
Piston Rod 8.jpg (291.85 KiB) Viewed 10598 times
Lubrication for the wrist pin comes from the standard. Drill passageways on both sides of the crosshead.
Piston Rod 9.jpg
Piston Rod 9.jpg (253.82 KiB) Viewed 10598 times
The piston connects to the rod with a taper and nut. If you really trust the accuracy of the plan, go ahead and machine the taper and thread. I decided to do the bottom cylinder cover first, then do a “checkpoint” before going further. So, next time is the bottom cylinder cover.
Take care, Bob
Bob Sorenson, Harrisburg, South Dakota
apm
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Re: Stuart Turner 5a Build

Post by apm »

Bob I'm studying your pictures closely as I'm getting ready to try making my own crankshaft with similar silver soldering methods. Did you have any heat distortion or issues with the final crank? I don't see any photos of any post soldering grinding or turning. Did the silver soldered rod clean up with a little emery cloth only?
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xo18thfa
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Re: Stuart Turner 5a Build

Post by xo18thfa »

Hi apm. The crank rod itself was soldered together from ¾” diameter stock. The web pieces and wrist pin were turned to final dimensions. I covered the wrist pin in flux as much as possible to protect it from oxidation. After soldering, the crank rod was turned between a collet and center on the tailstock.

Crankshaft 5.jpg
Crankshaft 5.jpg (263.04 KiB) Viewed 5785 times


The 5a crankshaft has 11/16” diameter bearing surface and 5/8” diameter for the flywheel and eccentric. Since there are 2 diameters anyway, I decided to turn it this way to eliminate any warp. There was no warp anywhere along the way. It stayed straight after cutting out the middle. The crank is alloy 1144 stressproof. It machines very well.
I contacted Andrew at Stuart before starting the crank, to see what they recommend. He said they have a vendor that silver solders their cranks for the 5a.

Thanks, Bob
Bob Sorenson, Harrisburg, South Dakota
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xo18thfa
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Re: Stuart Turner 5a Build

Post by xo18thfa »

Today are the top and bottom cylinder covers. These are a fairly straight forward turning process. The covers are cast iron, with no cast bosses to help in the turning process. However, there is enough material to grip during the machine steps. As with all the other castings, they are way over size and none of the original cast surface will remain.

I decided to do one major departure from the plans. The bottom cylinder cover plan calls for a 1-1/8 x 16 TPI male thread to accept a corresponding blind threaded cap to retain a solid bronze packing bushing. I reviewed some old books I have on steam engine design and did not see this method on other engines. After long deliberation and consultation with my shop mentor, I decided to go with a more traditional two bolt bushing retaining method. But, instead of packing the gland with graphite yard, as is traditional, I also decided to use an O ring for the seal. Kozo Hiraoka has an article with specifications on O ring packings in one of his books, so I went with that.

The piston rod is 13/32” diameter. And, of course, our local hardware store has every O ring in the visible universe, except 13/32” ID. Fortunately, 10mm ID is extremely close, so that’s what’s in there.

Start out by turning the cover to its final dimensions on the lathe.
Top and Bottom Covers 1.jpg
Top and Bottom Covers 1.jpg (265.97 KiB) Viewed 5765 times
Drill for #10 x 32 clearance and #4 x 40 for the gland.
Top and Bottom Covers 2.jpg
Top and Bottom Covers 2.jpg (251.45 KiB) Viewed 5765 times
Fabricate a gland nut and the bottom cover is done.
Top and Bottom Covers 3.jpg
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The top cover has a very nice domed center. Pretty much have the freehand that feature in.
Top and Bottom Covers 4.jpg
Top and Bottom Covers 4.jpg (207.46 KiB) Viewed 5765 times
At this point verify the total length of the piston rod. History shows that errors creep in and sometimes plans are not correct. This time, however, everything was right on.
Top and Bottom Covers 5.jpg
Top and Bottom Covers 5.jpg (227.18 KiB) Viewed 5765 times
Set the lathe compound to 6 degrees to turn the taper to retain the piston. Turn a straight portion to 5/16” diameter for the piston nut. Thread with either 5/16 x 32 or 5/16 x 40. The piston rod casting is long enough to do the lathe work in one setup. Do not disturb the compound setting until the piston is done.
Top and Bottom Covers 6.jpg
Top and Bottom Covers 6.jpg (266.88 KiB) Viewed 5765 times
Next time we’ll get started on the cylinder.

Take care, Bob.
Bob Sorenson, Harrisburg, South Dakota
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xo18thfa
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Re: Stuart Turner 5a Build

Post by xo18thfa »

Starting on the cylinder today. The Stuart 5a cylinder casting is wonderful. It is spot on in dimensions and is wonderful to machine. The steam ports and exhaust are right on dimension and very sharp. The cores are clean and uniform all the way thru. No work at all was needed on any of that. The first step is mount up in the three-jaw chuck, rough face the end and rough bore all the way thru, about 2” ID or so.
Cylinder 1.jpg
Cylinder 1.jpg (256.67 KiB) Viewed 2280 times
Opps. The chuck jaws foul the boring bar going all the way thru. So, switch to the four-jaw and use parallels for stand offs.
Cylinder 2.jpg
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Now get it rough bored all the way thru.
Cylinder 3.jpg
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I was concerned crushing the cylinder in the four-jaw and distorting the bore. So, I switched over the faceplate and gripped the cylinder casting by the flange. The finishing passes were taken with a sharp, broad nosed HHS tool in a ¾” diameter boring bar. Use a telescoping bore gage to creep up on the final bore. Check in several places to make sure the bore is parallel. I got really lucky on this task. The boring bar left perfect finish and everything straight and true. Do a light skim facing cut to finish.
Cylinder 4.jpg
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Lightly hone the cylinder bore. It won’t take much.
Cylinder 5.jpg
Cylinder 5.jpg (235.52 KiB) Viewed 2280 times
The cylinder bore is 2.250”. The registration spigots on the covers are 2.312”. If the engine ever needs a rebore, the covers will be undisturbed. Turn a corresponding recess for the cylinder covers about 0.040” deep. Turn the cylinder around and rest on the faceplate to get the other end. Lightly face the cylinder end to its final height.
Cylinder 6.jpg
Cylinder 6.jpg (307.47 KiB) Viewed 2280 times
That’s it for now. Next time we’ll get on the portface.

Take care, Bob.
Bob Sorenson, Harrisburg, South Dakota
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