Moriya Stirling Engine Build

[NP317]

Nice progress, Russell.
My students experimented with static and dynamic balancing of this Stirling fan. It was a fun and educational engineering exercise.
The fan turning on my wood stove has counter weights installed on the original rectangular cranks on the displacer piston.
It helps the dynamic balance some, but I don't think the gains in operation are worth that effort.
I'll be interested in how your crank discs work.

The main crank shaft was left in one piece until the 45% silver brazing to the cranks was complete, then the center cut out and filed smooth on the cranks.
We would chuck the assembly in the lathe (collet chuck) for final "cleaning", some of which was done before cutting out the shaft center.
Having flat cranks made alignment and brazing simple. Your round discs might make silver brazing (and alignment) more difficult, because of their increased thermal mass.
A different joining method could be required. And it needs to tolerate heat.

And we used small ball bearings (1/4" I.D., 1/2"? O.D.) in the two support towers which have proven to be a hardy solution.
I don't remember what the original design of the crankshaft bearings was.
The towers we made had pockets machined to hold the bearings. We machined those towers on a CNC mill, as part of the educational process.
I think I even have more of those open-ball bearings I can send to you, if interested.
RussN

[rmac]

Thanks again, RussN, for the hints!

Now that you point it out, I can see where it would be easier to align the cranks if they were made according to the original plans. I might change my mind on that.

I thought about trying to give the cranks the funny pie-shape that you see on some engines for balance, but 1) I don't know how to design the shape so it would actually help, and 2) I'm guessing (as you found out with your model) that it wouldn't make much difference anyway since the displacer connecting rod is made from aluminum and therefore relatively light weight.

The original article calls for the crankshaft to be assembled with soft solder. But I found a copy of the plans on the University of Washington website that had been marked by hand (perhaps by you?!?) to use silver solder. Silver solder is stronger, but there's less chance of distorting the parts (due to heat) with soft solder. Interesting tradeoff.

For the record, here's a link to those marked-up drawings:

http://courses.washington.edu/me355b/Bl ... Fansan.pdf

I also found on the same website a page from about 2015 with a link to a SolidWorks model of the same engine. Here's that link:

http://courses.washington.edu/me355b/labs.html

Today's chore is to inventory my scrap pile and make a shopping list for the stuff I don't have already.

-- Russell Mac

[Harold_V]

The original article calls for the crankshaft to be assembled with soft solder. But I found a copy of the plans on the University of Washington website that had been marked by hand (perhaps by you?!?) to use silver solder. Silver solder is stronger, but there's less chance of distorting the parts (due to heat) with soft solder. Interesting tradeoff.

There is an option, although it isn't as strong as silver brazing.
I built the hydronic heating panels for my shop and house. I used silver bearing solder for all of the connections. It's much like working with soft solder, but stronger. Not cheap, but worth the difference. One of the choices (Harris STAY-BRITE #8) offers up to 6% silver content. Keep an eye on eBay and you may find a deal. I did!

No, I don't own stock in Harris. Just a satisfied customer.

H

[rmac]

I built the hydronic heating panels for my shop and house. I used silver bearing solder for all of the connections. It's much like working with soft solder, but stronger. Not cheap, but worth the difference. One of the choices (Harris STAY-BRITE #8) offers up to 6% silver content. Keep an eye on eBay and you may find a deal. I did!

Yeah, I've actually got all the stuff (solder and flux) and use it once in a while to paste broken band saw blades back together.

-- Russell Mac

PS to Harold: Any chance you can do some moderator magic and change the title of this thread? Something like "Moriya Stirling Engine Build" would make a lot more sense going forward.

[Harold_V]

PS to Harold: Any chance you can do some moderator magic and change the title of this thread? Something like "Moriya Stirling Engine Build" would make a lot more sense going forward.

Done!

The original post has been changed, so a search will yield success by your chosen title. I did not go to the trouble to edit each of the posts in the thread, however. If you feel that's necessary, I can do so.

H

[NP317]

RusselL:
Yes, that marked drawing is the one I marked up early on in that class, many years ago. How funny to see it again!
Memories from my wonderful University of Washington, Seattle, job.

Also, the webpages on the Mechanical Engineering 355 class Manufacturing Processes, were well produced by the person I hired and trained to take over when I left to be the Maintenance Manager for the rebuild of the historic Seattle Monorail system in Seattle.
I am still in contact with Eamon McQuaide, a very talented person to take over from me. He has continued to advance the technologies offered to Engineering students at the UofW.

Some notes:
The towers supporting the crank shaft can be made per the original drawing, assuming you find the small ball bearings to fit.
I modified it because we had a drawer full (literally) of the larger OD ball bearings to use. One of the joys of inheriting a shop that dated back to 1906!

The displacer piston body I specified as thin-walled stainless steel tubing, again because we had lots of it. Aluminum will be lighter, and probable better for the engine operation. Heat expansion probably would not be a problem. I never made an aluminum displacer piston body.

Memory lane for me. Thanks.

And Thanks to Harold for changing this thread name for clarity.
RussN

[rmac]

Harold: Thanks for fixing the thread name. That'll definitely work better if somebody happens to be interested in this particular engine.

RussN: I haven't tried to source the crankshaft bearings yet, but my plan at this point is to follow the original design for the support towers. I don't even have a DRO, let alone CNC capability!

The article says, "Aluminum is used for the displacer piston in the interest of light weight and ease of construction. Thermodynamically, a thin walled stainless steel piston would be much better." I figured maybe that's why you went with stainless steel. As far as performance goes, the tradeoff between the two materials seems to be one of weight vs. thermodynamics. I have no clue how to judge that. As for "ease of construction", McMaster Carr has some stainless tubing that looks perfect. That seems easier to me than trying to bore out a flimsy thin walled aluminum tube.

This afternoon I came up with my shopping list and one new question: The plans specify aluminum for the four long bolts that clamp the cold and hot ends of the displacer cylinder to the base. Seems to me that these would be better made from steel in order to minimize heat transfer between the hot and cold ends. Any idea why the plans call for aluminum?

-- Russell Mac

[AllenH59]

I remember reading that a Stirling engine would do 3500 rpm...

[NP317]

Russell:
We made the four main cylinder bolts from drill rod. No problems, and I had good in-shop stock of it. Mild steel rod would also be fine to use.
I don't know why those rods were called out to be made from aluminum. Maybe that's what the designer had in hand?

And your plan to purchase the SS tubing for the displacer cylinder sounds good to me.
I often choose to purchase materials close to finish dimensions to make my projects easier/simpler to machine.
RussN

[rmac]

Progress Report #2

I got started on the hot end of the engine today using some material from the scrap pile. I decided to make two sets of parts. I figure if I get lucky I'll be able to find some combination thereof that will result in a running engine. And if I get really lucky, I'll have two!

The tubular part started out as plain old 1" electrical conduit. As luck would have it, the conduit's ID was a little less and its OD was a little more than the dimensions specified for the engine. So I was able to bore out the inside and whittle away at the outside to produce the required tube. The wall thickness is nominally 0.025". I was kind of nervous about that part, but I took it easy and had no trouble.

This was my first time silver soldering anything besides band saw blades. That was way easier than I thought it would be.

I still have to solder on some end caps, but I thought it might be better to do that near the end of the project because it might be useful to see inside the cylinder to make sure the displacer piston is centered properly.

-- Russell Mac

[NP317]

Russell:
Really familiar looking hot ends! And nice job machining, brazing, and cleaning them!!
Looking award to seeing what follows.
We always went ahead and brazed the end caps on. Making the rest of the parts per the drawings always worked in the end.
RussN

[rmac]

We always went ahead and brazed the end caps on. Making the rest of the parts per the drawings always worked in the end.

Yeah, I know that's how it's supposed to work. But that 0.030" clearance between the displacer piston and the cylinder wall has me scared. I keep having nightmares where something's just a little crooked and the piston is scraping the wall. Maybe I worry too much.

-- Russell Mac