Bob J's No.21 Steam Engine (drawings and STP files by Pat J)

GreenTwin · Dec 5, 2024

The slot in the piston is 0.0640" deep, so Jason's suggestion seems about right.
This was my dad's engine design, and the measurements came from his disassembled engine.
I think I overlooked that dimension, but I don't think it is too critical.

This is my dad's engine disassembled.
.

GreenTwin · Dec 5, 2024

I attempted a group build with this engine many years ago, but it was somewhat of a failure on my part due to my almost complete lack of engine building experience.
I think two in the group completed working engines, but I never completed mine.
This engine seems easy now.
If I knew then what I know now............looking back, I have come a long way.

Here are some rings I made.
.

Jasonb · Dec 6, 2024

Pat I was not suggesting a size. I took it off what you had drawn but not put a dimension against on the 2D drawings.

Might be worth adding the more usable STEP files again as the old link no longer works.

GreenTwin · Dec 6, 2024

Those are actually STL files loaded to this site, but you are correct, they no longer work.
I wonder what is up with that?

Folks will have to figure out the best ring thickness.
Any number I add for that on the drawings would just be a guess.
I don't think it is a critical dimension.

I am a bit busy at the moment to go back and recreate new STL or STEP files, but will add that to my list.
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Jasonb · Dec 6, 2024

No the STL files work fine at least they do for me. as that is what I opened to get the ring thickness. but that is not a good file type.

It is the link to the Step files that is dead.

timo_gross · Dec 6, 2024

Jasonb said:
No the STL files work fine at least they do for me. as that is what I opened to get the ring thickness. but that is not a good file type.

It is the link to the Step files that is dead.

How did you open them? I get weird things when trying.

I answer myself: "right-click" then press "save-link-as" and confirm save. Then I was able to open the STL on my 3d printing program.

STL files are fine for most 3d printing enthusiasts, but Step files are more usable for modification and machining.

Jasonb · Dec 6, 2024

Clicked the file in pats post and it downloaded, then opened it in F360. used the measure tool to get the thickness between two points.

I usually use Alibre but that won't open STL though it does export them.

salmonr · Dec 6, 2024

GreenTwin said:
I attempted a group build with this engine many years ago, but it was somewhat of a failure on my part due to my almost complete lack of engine building experience.
I think two in the group completed working engines, but I never completed mine.
This engine seems easy now.
If I knew then what I know now............looking back, I have come a long way.

Here are some rings I made.
.

salmonr · Dec 6, 2024

That's what I was after, information about the actual piston ring manufacture. The ring has the width , which is fine, the bottom of the slot dia is .996" . So when turning the rings what size bore and o/d do you work to , do you for instance make them oversize to allow for the slot gap ? Do you heat treat them ie use something other than cast iron, ? .drawing has cast iron , has this enough elasticity to prise open to get it into the slot without distorting the ring.Sorry for so many questions, as you can tell I'm new to piston ring manufacture and it saves time to ask knowledgeable people rather than trial and error.

bobcjohn · Dec 6, 2024

GreenTwin said:
My dad scratch built a nice little single-cylinder oscillator many years ago.

It is a relatively simple design, but looks nice, and so I thought I would post it here for those who may want to build it.

View attachment 138143 View attachment 138144

Thanks for the .stl files. Bought a 3D printer this year. Your dad's engine will make a fun first project.

GreenTwin · Dec 6, 2024

salmonr said:
That's what I was after, information about the actual piston ring manufacture. The ring has the width , which is fine, the bottom of the slot dia is .996" . So when turning the rings what size bore and o/d do you work to , do you for instance make them oversize to allow for the slot gap ? Do you heat treat them ie use something other than cast iron, ? .drawing has cast iron , has this enough elasticity to prise open to get it into the slot without distorting the ring.Sorry for so many questions, as you can tell I'm new to piston ring manufacture and it saves time to ask knowledgeable people rather than trial and error.

There are several ways to make cast iron piston rings.
For this very simple engine, I think a simple approach will suffice, unless you want to use a more complex method.
From the group build, as I recall, the rings were turned slightly oversized, cut, and a slight gap ground at the cut.
The ring was test fit in the bore, with some slight sanding with fine emory cloth at the cut, and a bit of space at the gap to allow for thermal expansion.
Not a perfect piston ring, but a very simple and workable piston ring.

The more complex rings are turned oversized, cut, compressed on a mandrel, and turned again, but that is not necessary on this engine as far as function.

.

salmonr · Dec 6, 2024

GreenTwin said:
There are several ways to make cast iron piston rings.
For this very simple engine, I think a simple approach will suffice, unless you want to use a more complex method.
From the group build, as I recall, the rings were turned slightly oversized, cut, and a slight gap ground at the cut.
The ring was test fit in the bore, with some slight sanding with fine emory cloth at the cut, and a bit of space at the gap to allow for thermal expansion.
Not a perfect piston ring, but a very simple and workable piston ring.

The more complex rings are turned oversized, cut, compressed on a mandrel, and turned again, but that is not necessary on this engine as far as function.

.

Thanks for that , the rings are the only thing I could see that was not straight forward. I'm going to machine the base out of solid 2 1/2 ×2 1/2, rather than solder the other bearing carrier. Might take a bit of time but that's the only thing I've got which is free !

Jasonb · Dec 7, 2024

You could always use an O ring or if you are just running it for display or lightly loaded then you don't even need a ring of any sort.

When I do make iron rings I turn the OD to fit the bore of the cylinder, split them and stretch over a mandrel then heat treat. This will "set" them in the stretched position so that they need to be compressed to fit into the bore.

salmonr · Dec 7, 2024

Thanks Jason , some good methods there.

Richard Hed · Dec 7, 2024

salmonr said:
Thanks for that , the rings are the only thing I could see that was not straight forward. I'm going to machine the base out of solid 2 1/2 ×2 1/2, rather than solder the other bearing carrier. Might take a bit of time but that's the only thing I've got which is free !

If you look around in this forum you will find a WHOLE LOT of discussions on piston rings. I don't know where they are as I am not going to make any, but I was interested how peeps did it and there were a LOT of good methods

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