Author Topic: Howell Stirling Engine Fan  (Read 6123 times)

Offline RReid

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Re: Howell Stirling Engine Fan
« Reply #45 on: January 24, 2022, 12:24:00 AM »
It made sense to work on the Fan Hub next, as it goes onto the opposite end of the crankshaft from the crank arm finished yesterday. It is mostly a turning job, with some drilling and slots cut in to hold the fan blades. I'll wait until I have the blades made to actually cut those slots.

The hub started as a piece of 1.125 aluminum, which gets turned first to 1.1. Then the end that will be towards the crank is turned further, to 0.625 and a short little spigot just like the crank arm got is added. This bears up against the ball bearing. Finally a blind hole is drilled and reamed to 0.1875 to fit the crankshaft.


With that end done the part is turned around. Since it will now be chucked on the already turned surface I use some bits of brass over the jaws to protect the finish. This end also gets turned down to 0.625. Then the end is to be rounded off.


I have a Taig radius tool that they sent me by mistake some time back, so I was thinking this would be a perfect chance to use it. But I forgot that, by it's design, it needs at least 1.5 of part hanging out beyond the chuck or the tool won't clear. So I started thinking of cutting stair step segments and finishing those off with a file. Then I remembered Jo's recent post in which she used a corner rounding router bit is a similar situation. Eureka!

Worked a treat. Thanks Jo!





Regards,
Ron

Offline Kim

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Re: Howell Stirling Engine Fan
« Reply #46 on: January 24, 2022, 01:18:07 AM »
Nice work on the fan hub, Ron!  :popcorn: :popcorn:

And great use of the router bit trick!

Kim

Offline RReid

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Re: Howell Stirling Engine Fan
« Reply #47 on: January 24, 2022, 03:06:03 PM »
Thanks Kim! I love picking up tricks like that, and the great folks on MEM are a prime source.
Regards,
Ron

Offline bent

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Re: Howell Stirling Engine Fan
« Reply #48 on: January 24, 2022, 06:49:09 PM »
Nice hub, love that use (again) of a router bit for a large radius cutter.  :popcorn:

Offline RReid

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Re: Howell Stirling Engine Fan
« Reply #49 on: January 24, 2022, 08:49:40 PM »
Thank you, Bent!

And now, here's a tale of a close call. The bore of the fan hub turned out to be a bit tight for the drill rod used in the crankshaft. Other pieces of drill rod of the same size fit fine, but of course not the one that matters! So I was massaging the hole and checking it with a piece of rod from the same mother stock as the crankshaft. It was going well and I had a good fit down to about 2/3 the length of the bore, when the sample rod grabbed. I was holding and turning it by hand in a dismounted drill chuck, not meaning to force things, but guess I tried just a bit too hard and it grabbed and grabbed hard. Then nothing I tried, including the use of a heat gun on the hub, could loosen it, partly because it was difficult to hold either piece very securely or bring much force to bear.

In the end, I chucked it back up on the lathe, clocking it in as perfectly as I could (I got it to where the needle of the indicator was just barely moving). Then I cut off  the protruding rod and drilled through the 0.1875 remainder with a #14 (0.1820) drill. Luckily this worked well, and most of the offending rod came out as a partial shell without harming the original bore.




Then I was able to run an old, short, and reliable 3/16 drill in to open it up just that tiny bit needed, and clean up the marks I had made on the face and chamfer in the earlier attempts. Crisis resolved and now it fits fine and without any wobble. Whew!

Regards,
Ron

Offline crueby

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Re: Howell Stirling Engine Fan
« Reply #50 on: January 24, 2022, 08:54:14 PM »
Close call! If you were making a movie it would have been a nice suspense building scene...


 :popcorn: :popcorn: :popcorn:

Offline RReid

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Re: Howell Stirling Engine Fan
« Reply #51 on: January 24, 2022, 09:08:34 PM »
Stay tuned for Alfred Hitchcock's "The Model Engineer".
Regards,
Ron

Offline crueby

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Re: Howell Stirling Engine Fan
« Reply #52 on: January 24, 2022, 09:14:37 PM »
Stay tuned for Alfred Hitchcock's "The Model Engineer".
I'm peering over the back of the couch. With popcorn ready!

Offline Kim

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Re: Howell Stirling Engine Fan
« Reply #53 on: January 24, 2022, 09:43:48 PM »
Yes, sounds like some tense moments!  But you came through with a good save!  :ThumbsUp:

Well done, Ron,
Kim

Offline RReid

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Re: Howell Stirling Engine Fan
« Reply #54 on: January 25, 2022, 03:23:15 AM »
Thanks Kim. I try not to get too stressed about these things; they happen and it wouldn't have been a difficult part to remake. But still, I was pretty relieved and happy that I didn't have to!

And Chris -  :lolb:
« Last Edit: January 25, 2022, 02:56:16 PM by RReid »
Regards,
Ron

Offline RReid

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Re: Howell Stirling Engine Fan
« Reply #55 on: January 27, 2022, 02:59:36 AM »
Work has been proceeding on what is called the Hot Cap. This is the part that transfers the heat of an alcohol flame into the displacer cylinder, while limiting heat loss to the surrounding structure. It is preferably made of stainless steel.

On one of our trips to visit our son in TX, I was given several rods of stainless, 2 of 1 diameter and one of 3/4. These are of unknown alloy, but are non-magnetic, so likely 300 series. As a test, I cut a piece off, chucked it in the lathe, and tried turning it to the smaller diameter specified in the plans for the hot cap. It machined pretty easily, so is probably 303, maybe 304. That made me happy, since I once had to machine some 316 SS with a small and tired Jet lathe, and it was an unholy chore, even using the old braze-on carbide tooling I still had in my toolbox.

Anyway, since the material choice was a go, I proceeded over to the mill to cut the called for crenellations in the top.


Then back to the lathe to create the 1.55 deep by 0.94 bore, which leaves a rather thin wall in a 0.965 OD! I got it out to 0.43125 with drills.


Then the rest of the way with a boring bar. That boring bar, by the way, came from the same source as the SS rod. In the picture the bore is almost, but not quite, done. Regardless of the grade of SS, with no power feed this was a tiresome bit of work.


There is still a mounting flange make and attach. The plans show the part as a single piece, but ,as with the power cylinder, I am opting to make the flange separately. I will modify a SS washer to fit for the purpose.
Regards,
Ron

Offline RReid

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Re: Howell Stirling Engine Fan
« Reply #56 on: January 27, 2022, 10:36:24 PM »
No work in the shop today. We took a drive over to the coast instead. An absolutely gorgeous mid-winter day.




Regards,
Ron

Offline Flyboy Jim

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Re: Howell Stirling Engine Fan
« Reply #57 on: January 28, 2022, 06:29:11 PM »
No work in the shop today. We took a drive over to the coast instead. An absolutely gorgeous mid-winter day.

Looks like a day well spent.

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 Dave Otto

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Re: Howell Stirling Engine Fan
« Reply #58 on: January 28, 2022, 08:47:40 PM »
Beautiful photos Ron!

Dave

Offline RReid

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Re: Howell Stirling Engine Fan
« Reply #59 on: January 29, 2022, 12:22:24 AM »
Jim and Dave Thanks guys! It really was a nice day. Now back to SERIOUS business.  :)

To make the base for the hot cap I started with a 7/8 SS washer. This had an ID just a bit smaller than the finish size needed, and an OD quite a bit larger. I re-used a fixture made for the Radial Five build that screws to the face plate. A small adjustment to the center spigot was all that was needed to center the washer and fasten it through the central threaded hole. This allowed me to turn the OD from about 2 down to 1.5.


Next the fixture was transferred to the mill for drilling and tapping of the 4-40 mounting holes.


Then back to the lathe. With the washer held on place by the mounting screws and the central fixture screw removed I could bore the ID for a press fit onto the hot cap.


To minimize the stress on the thin wall of the hot cap, I heated the washer in the toaster oven (medium toast) before pressing them together. Worked out great. That base isn't going anywhere.



Regards,
Ron