"Catherine", a USA "Sweet Pea" engine build

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Harold_V
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Harold_V »

Marty_Knox wrote:Harold, I'm going to disagree with you about honing - it IS used to precisely size bores. But you can't do it with a hand held hone. Go to a good automotive machine shop and see if they have a Sunnen Cylinder King. It's an amazing machine that can hone a cylinder to the exact size and finish you want.
I wasn't discussing a Sunnen cylinder king, as that's not what's being applied in the posted picture. What is posted is the typical three stone spring loaded cylinder hone, which is incapable of controlling the end result, unlike the Sunnen. That was my point. Spring loaded stones don't have the ability to correct bore errors. If a bore is elliptical, it will remain elliptical, and taper can be corrected only by chance, even when one attempts correction. As I said, hones such as the one being displayed are intended for breaking glaze, or maybe even improving surface finish (remove feed lines), not for sizing. But they do so with risks, as I mentioned.

In regards to surface finish, the conditions in a steam cylinder are very different from conditions in an internal combustion engine. Depending on the nature of the rings being used, a fine finish may be desirable (O ring or string packing). Cross hatch is expected for metallic rings, so seating is accelerated, but seating of rings for steam isn't a requirement unless they fit poorly at the outset, as the pressure in steam cylinders is extremely low as compared to internal combustion, so there's typically very little bypass, if any.

Harold
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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi »

The piston rods started out as some 3/8” diameter stainless steel rod (probably 303 or 304) which I turned down and then threaded 1/4-28. I made the threaded portions longer than called for on the plans because I plan to secure the piston to the rod with a nut on each end (which is also why the cylinder covers had a recess milled on the inside to clear the nut. I can’t say I hate cutting threads but I never seem to get them as clean as they come on finished hardware from the store.

Trimming them to length on the bandsaw was a difficult proposition because the rods kept wanting to spin and I didn’t want to use clamps which would nick or damage the finish on the rods. So, the old handsaw came out and made quick work of it.

After having realized earlier in the project that Allen Model’s mogul had the same cylinder diameter (2”) as my revised Sweet William, I called Marty up for some bronze to use for the pistons. The mogul’s pistons are slightly shorter than the SW’s pistons, but I figured it would be okay. I faced the bronze blanks on both sides and then cut slight recesses on both ends for the nuts. Then, they were drilled and tapped ¼-28 to match the pistons.

Unfortunately, my threading of the pistons didn’t allow for the rods to completely screw down to the hard shoulder where the threading stopped on the rod, so I thought perhaps cutting a slight countersink on the ends of the pistons would fix this. Unfortunately, I used a larger drill bit instead of a flat bit and the brass grabbed the bit and pulled it entirely through the piston blank, ruining it. The second piston was done with a flat bit without any trouble.

Seeing as I had to order at least one more piston blank from Marty, I had him cut them to the length I needed and I restarted the process. It means that I can make three pistons and have one as a spare should I mess anything up again.

Some people mount the pistons on the piston rods and then turn the piston’s edges and grooves at that time. This ensures that everything is balanced and square. However, using my wrecked piston as a test case I discovered that I couldn’t turn the piston when it was solely supported by the piston rod in the lathe chuck. Any pressure from the sharp cutter on the piston caused the rod to bend, which obviously wasn’t good.

A solution my friend came up with was to chuck the piston on a long ¼-28 bolt with threaded rod connectors on each end. Then, one end was chucked in the lathe in a collet and the other was supported on the tailstock.
Attachments
Piston and threaded rod connectors.jpg
turning piston.jpg
Last edited by Benjamin Maggi on Fri May 01, 2015 5:52 am, edited 1 time in total.
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"
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Dick_Morris
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Dick_Morris »

Trimming them to length on the bandsaw was a difficult proposition because the rods kept wanting to spin and I didn’t want to use clamps
If your bandsaw has a table try holding round stock with an upside down drill press vice.
SilverSanJuan
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by SilverSanJuan »

Hi Ben,

How did you thread the piston rod? Did use a die, or cut them with a lathe tool? I haven't cut threads on my lathe yet, but I think it's about time to learn. I can't seem to get nice square threads with a die, even when using a threading fixture.

Todd
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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi »

I cut the piston rod's threads on the lathe, because I was concerned using a die could lead to threads that were not square.
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"
Kimball McGinley
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Kimball McGinley »

Regarding how you turned the piston, with the bolt and coupling nuts; I cannot see how that could possibly ensure that their is no run-out between the threads and the piston O.D. Am I missing something here?
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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi »

The two pistons had their slots cut in with a very sharp, thin bit. I also made a spare piston as well (though it is sized to work in the smaller of the cylinders due to different bore sizes). Some cleanup of the sharp raised edges of the slot with abrasive paper finished them up. Since the two cylinders have slightly different bore sizes I had to do each piston to correspond with each cylinder. In the end, I am happy with how they came out.
Attachments
piston ring slots cut.jpg
pistons in cylinder.jpg
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"
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ironhorseriley
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by ironhorseriley »

I hope I am not disrupting the flow of events on the progress of this project. The three Sweet William builds referenced on this thread including this one are all for 7-1/4" gauge models. If the builder is going for 7.5" gauge, do the plans make allowance for that in reference notes or are you on your own? I pondered that it may be a case of just incorporating shims on the cylinder mounts for moving them slightly outward and spacers on the wider gauge drive wheel sets. That way the locomotive could in theory be regauged back to 7.25" gauge if another owner down the road wanted to, allowing for building the frame as is. Or am I goofed up on this?

Jim
Jim, Former railroader, fascinated by wood working & “all things engineered”.
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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi »

I just checked and at least some of the plans (like the frame stretchers) are marked for dual gauges (7.25. 7.5). Things like the axles and stretchers. So, it shouldn't be difficult.
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"
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ironhorseriley
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by ironhorseriley »

I came across these 2 related short video links of a completed Sweet William under steam test for the first time. Great inspiration for this build!

https://www.youtube.com/watch?v=hg6MnH-Q6s0



https://www.youtube.com/watch?v=kFoj9LdH_H8

Jim, Former railroader, fascinated by wood working & “all things engineered”.
dbyam
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by dbyam »

Ben, thanks for your permission to post this information on your Build Log. My SW build has created several items of tooling that I no longer need. Perhaps there is someone reading this that has use for these tools. I have a frame, jig, or whatever you call it, fabricated to hold the 6" frame pcs. on a turret mill, A wheel Jig, Large steel cylinders used to help hold the steam cylinders for boring on a mill, quartering jig, and several other clamps and mandrels. If someone wants them I am willing to part with them for the cost of the freight, in hope that they may be further passed along.Please PM me if you have interest. :D I have Photos on request.

Doug
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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi »

Finally... I get to work on something besides the cylinders!

The steam chests started off as some of the same Durabar cast iron that I had used for the cylinders. When we originally divided up the chunk I bought, we took care to make sure to make cuts which would result in large enough pieces for the steam chests. It was close but not perfect. The optimal way was to lay it so the two spigots on the sides end up shorter than called for by about 3/8” each. This may affect performance so I might weld or screw on another round piece to make up the difference.

Since layout on cast iron with blue dye isn’t always easy on my eyes, I sprayed one side with white paint and then laid it out with a marker. Then, to make sawing out the middle portion easier, I chain drilled ¼” diameter holes all on the inside of the rectangle that had to be removed. One slid out of the area but the rest were okay. The cast iron heated up after about 5 holes so I had to frequently stop and let it all cool down.
Attachments
drilled out steam chests.jpg
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"
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