Author Topic: Howell Stirling Engine Fan  (Read 6276 times)

Offline RReid

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Howell Stirling Engine Fan
« on: December 28, 2021, 12:52:59 AM »
For my next project I've decided to build Jerry Howell's “Super Stirling Engine Fan”. I first learned about Stirling engines many years ago when we used one in an engineering school thermodynamics lab on measuring engine efficiency. I thought it'd be interesting to build one then but I had no tools, no money, no time, and not enough knowledge. Now I have at least some of those things. Unlike my other engines, this one can even serve a practical purpose! Here's a photo from the website (http://www.model-engine-plans.com).


Work actually commenced before Christmas with the “displacer head”. This was a fairly straightforward milling task. Not having any ball end mills, I used a 1/8” router bit to round off the bottoms of the two wide intersecting channels.




With that done, and a few days of family time, I moved on today to the “displacer cylinder”. That's the larger, silvery bit with all the fins in the stock photo. The first step was to cut a rough, approximate sized block from a disc of 1.5” aluminum I have.


A flycutter was used to square up two edges. Even though the cuts were kept light, the C-clamp added a bit of extra comfort on the second, hangy-outy edge shown here.




Then the rest of the lines were laid out and rough cut on the bandsaw.




At this point I moved the piece over to the lathe to begin boring the cylinder, starting with a few drills from 3/16” up to 1/2”.


In a few days I'll continue with a boring bar to get to the final 0.940” diameter.
Regards,
Ron

Offline Jasonb

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Re: Howell Stirling Engine Fan
« Reply #1 on: December 28, 2021, 10:17:52 AM »
Off to a good start. I have been toying with the idea of doing a Raab or Jost engine, possibly as a fan which they mostly made or just as a stand alone engine.

Offline Flyboy Jim

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Re: Howell Stirling Engine Fan
« Reply #2 on: December 28, 2021, 02:14:16 PM »
Good start and writeup.  :ThumbsUp:

I'll be following along on your project.

Jim
Sherline 4400 Lathe
Sherline 5400 Mill
"You can do small things on big machines, but you can do small things on small machines".

Offline RReid

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Re: Howell Stirling Engine Fan
« Reply #3 on: December 29, 2021, 03:20:50 AM »
Thanks Jason. I looked up Raab and Jost, can definitely see the heritage behind the one I'm doing. They have more Victorian finery though!

Thank you, Jim. Happy to have you along!
Regards,
Ron

Offline Bear

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Re: Howell Stirling Engine Fan
« Reply #4 on: December 29, 2021, 03:50:36 PM »
Pleased to see a Stirling build. Will be watching closely. Been contemplating making one; but have been deterred by comments I have read about the precision required to make them run. Maybe this thread will give me the courage to give it a go.

Offline RReid

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Re: Howell Stirling Engine Fan
« Reply #5 on: January 01, 2022, 03:29:24 AM »
Got the bore of the displacer cylinder finished. On to the the next step; finishing the surfaces to size and cutting the fins.




With the displacer head resting in place.
Regards,
Ron

Offline RReid

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Re: Howell Stirling Engine Fan
« Reply #6 on: January 03, 2022, 01:28:33 AM »
Since the last post, I've used the flycutter to bring all the sides of the displacer cylinder body to size, with the exception of the L-shaped side, where the flycutter couldn't get into the corner. For that I used a 1/2” end mill to get both faces cleaned up in one set-up. That short leg of the L forms the base for the power cylinder.


Next I moved back over to the lathe for cutting the fins (or more precisely, the slots between the fins). But first I re-purposed one of the fixture pieces left over from the Radial Five build by mounting it on an arbor held in a collet and re-cutting the spigot to fit the cylinder bore. This piece can be seen sitting on the cross slide.


That way I could use my heavy fixed center to support to work for cutting the fins. These require fairly deep plunge cuts, and the cuts are interrupted for over 60% of the way. I'm glad it's aluminum (or aluminium) rather than steel!


Got the first 9 roughed in by end of day. The slot width per plans is 0.093”. I've cut them using my 0.0625” cut-off tool. I plan to go back over them with a 0.093” tool, but I'll have to grind one up first. I'll need it to get the last slot or two up against the L cut as well, as the holder for the other tool won't let me snuggle up in there.
Regards,
Ron

Online Kim

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Re: Howell Stirling Engine Fan
« Reply #7 on: January 03, 2022, 05:27:43 AM »
Nice work on the fins, Ron!

I always found using the cutoff tool on the Taig a little harrowing.  It could be done, but it was slow and scary.  That's one thing I don't miss about a little lathe...  I agree - good that it was aluminum and not steel!  :o

Kim

Offline RReid

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Re: Howell Stirling Engine Fan
« Reply #8 on: January 03, 2022, 04:00:53 PM »
Thanks Kim!

I daydream sometimes about a bigger lathe (I miss the 13" LeBlond I had at one time), but with the space I have available it's just not an option right now. Making the little lathe do bigger work does add to the challenge, which I try to view as adding to the fun! That (relatively) large fixed center really does help a lot. And my youthful work in the deep well drilling machine shop included taking ~1/4+" deep interrupted cuts on cast steel up to 24" OD, which rather inured me to the noise and vibration. At least with this job I don't have hot blue chips flying everywhere!

I do like my lathe, but if Taig would make one that was just a bit bigger and heavier, more on par with the milling machine (which is excellent), and with thread cutting capability, then I might be seriously tempted.
Regards,
Ron

Offline bent

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Re: Howell Stirling Engine Fan
« Reply #9 on: January 03, 2022, 09:40:09 PM »
That looks fun, will be watching along, Ron! :popcorn:

Offline RReid

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Re: Howell Stirling Engine Fan
« Reply #10 on: January 05, 2022, 12:37:37 AM »
This morning I got a new 0.093” parting tool ground up that cuts virtually flush on one side so I could finish the last two fin slots up against that “L” leg, as well as go back through the other ones turning the fat fins into skinny ones.


I'm not sure if this two-stage process was really worth the extra effort or not, but now it's done. Apart from drilling mounting holes for the power cylinder, which I won't do until that part is made so I can match drill them, and some cleaning up of machine marks etc., that completes the displacer cylinder. The power cylinder will be brass, is smaller, round, and has fewer and shallower fins, so will be a bit easier. It does have a rectangular base, but I plan to do make that separately and silver solder the two together. But first I need to order some brass, cuz I don't have any around that's quite big enough for either part!



Regards,
Ron

Offline Minh Thanh

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Re: Howell Stirling Engine Fan
« Reply #11 on: January 05, 2022, 11:34:53 AM »
Look Great !

Online Kim

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Re: Howell Stirling Engine Fan
« Reply #12 on: January 05, 2022, 03:21:56 PM »
That's a lot of nice skinny looking cooling fins!  And done on a Taig no less - lot of work went into that!  :popcorn:

Kim

Offline RReid

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Re: Howell Stirling Engine Fan
« Reply #13 on: January 05, 2022, 03:26:13 PM »
Thank you,  Minh! Thank you, Kim.
Also Bear and Bent - glad to have you along!
Regards,
Ron

Offline Bear

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Re: Howell Stirling Engine Fan
« Reply #14 on: January 05, 2022, 03:42:56 PM »
Thanks, Ron. Pleased to be along. That is some pretty fantastic work  :ThumbsUp:.