# Small Sterling Fan



## shred (Jan 20, 2008)

After some discussions around the hot-air engine posted in the Plans area, I decided to get off my duff and make the mini-fan I've been thinking about for a while. Since I asked for this forum, I'm going to post parts as I make them, with plenty of commentary and gory details, and encourage others to do so too, no matter what their experience level.

I'm never one to follow directions exactly, so this one is mostly based on Jerry Howell's "Mini Sterling Fan" plans, but with modifications and additions from Dr Senft's Moriya (and the half-size version) and other things I think up. Hopefully it'll all work in the end, since this will be the first Stirling for me. Anybody with more experience is welcome to chime in with hints and other ideas as I track off into the deep end.

Much of the reason for building in this scale is I'm working with scraps from a friend's CNC machine shop. You'll note that "one inch" is a very common dimension for major parts, with very few larger than 1" in two dimensions. That works well for the scraps.

My usual pace is one part a night, though that varies a little. Somehow easy parts mostly end up taking all night too.. I'm definitely no Master of the Machine Shop, mostly self-taught and barely getting by on the experience from previous screwups.

So, going with the rake60 patented 'make the hard part first', I started off with the displacer cylinder. Jerry calls for this all to be one piece of metal, but not having a slitting-saw the right size and not being keen on long overhangs of the parting tool needed to clear the base, I elected to make this in two parts similar to Moriya. In addition, the parting tool I had handy wasn't the thickness specified for the fin spaces, so those also had to be resized.  Two design changes and I've not even made the first part yet. Poking in the scrap box, I went with brass for the finned piece and aluminum for the base. Brass conducts heat pretty well and it looks nice, so there it is.. Three changes, now..

Senft's instructions for fin cutting by putting the compound parallel to the lathe axis and cranking it to set the fin-space distance works. I started out with a table of spacings, but ended up just zeroing the dial and cranking the same distance each time.

Then, thinking about how to attach the the base, I thought ahead to the hot cap and how I had some nice 1" round stainless. The plans call for 1" square, which I don't have, but by moving the mounting screws in a little, not only could I add room to hold the fins on, but I could fit the mount screws into a 1" circle.  That turned out great. Even though there will be some insulators holding them apart in the end, 1" round fits perfectly inside the 2-56 SHCS heads holding the fins on. I'll probably counterbore them flush anyway, but I was impressed with my own serendipity 

(a note on the photos. Right now they're 'as-cast'. I'll tidy them up later, hopefully. (for scale, the fin block is 1"x1"x1.2")










Well, one weekend over and I have a new shiny paperweight, for small values of 'paper'.. Onward to the hot cap and power cylinder.


----------



## shred (Jan 20, 2008)

The Hot Cap is specified as "CRS or stainless, stainless much preferred" (for thermal reasons), so, not having worked with stainless since getting my 10" lathe, and thus having forgotten the irritation thereof, I went with stainless. I think the 1" round was 17-4, or at least my friend thinks it was. Anyway, my opinion of stainless hasn't improved. This stuff generated thousands of tiny porcupine needles that lept off the workpiece into my fingers, plus left an ugly finish (the source bar of course has a flawless smooth shiny finish)  

The hot cap is specified at 1.00" long, with a .950" deep bore and a .050 sidewall at the 'waist', to limit heat conduction. My cleverness here at not-wanting to dink with precisely boring a flat bottomed .950 hole was to bore it over deep (~1"), then measure and face it off so the hole was .950 deep. Probably old hat to the pros, but I was happy to have thought of it. After snapping one drill drilling out the stock, I tried a tip I read somewhere and clamped a 1/4" end mill into the boring bar holder with one flute on center as a mini boring bar-- that worked surprisingly well to enlarge the initial drill hole enough to get regular boring bars in.

The next smart thing (Jerry suggests this on his web site) was to turn up a close-fitting piece of Al with a center hole in one end. Putting that in the finished bore, it was easy to judge the wall thickness and prevent it from collapsing as I turned the outside profile, plus let me get the tailstock into the fray.






The plans call for 2-56 stainless screws to lower heat conduction. Asking around for some of those led me to an excellent bolt and fastener supply house just a few miles away-- no minimums and $0.03 apiece "how many do you want?". "how many you got?" "35" "ok, I'll take them" "that'll be $1.05, cash or charge?".  With a place like that I may have to abandon my usual practice of ordering small screws in the longest available size and grinding them down as needed.


----------



## Powder keg (Jan 20, 2008)

Great job so far! You could make one of those arbors with the flat spot on them that uses a small dowel to cam the piece tight. Using this, Use some Emery and sand the hot cap to a shiny finish. 

Wes


----------



## shred (Jan 20, 2008)

Jerry's plans have the power cylinder with fins. I'm not sure why except maybe to look cool, since few others I've seen have them. Stirling gurus, is there a thermal reason I'd want a cool power cylinder?

Anyway, I had some 7/8" brass rod ends and sorta-finned mine. Turns out my parting tool had got loose and the fins were only about half as deep as the plans show, so they'll be even less useful, if they ever were. After drilling and boring the cylinder, I turned up another close-fitting piece of Al and with a little JB Bore compound, lapped out the bore. JB is used to clean heavy deposits of copper and lead out of rifle barrels and works great for light lapping (plus I have a ton of sample jars)

The 7/8"-ness of the stock rod almost got me in trouble with the mounting screws-- I didn't check beforehand and they only barely fit (Aside: I drilled the displacer base already on my little CNC-- I've taken to drilling not quite all the way through to avoid drilling into my parallels and finishing the last little bit on the drill press. So far it's worked well)

I milled the flats using another little trick I picked up a while back for no particular reason-- my screwless vice has a little v-notch in the center. Makes it easy to hold and locate round stock with an edgefinder off the sides of the vice. Anyway, In order to mill the flats on the cylinder base full depth without setting the top of the cylinder up on parallels, I drilled a 3/4" hole in some smooth scrap .125" Lexan, put the power cylinder top-down through the hole, clamped it so the lexan acts as a sacrificial spacer between the part and vice and milled the flats. I should go back and stage a photo of that.


----------



## shred (Jan 20, 2008)

Powder keg  said:
			
		

> Great job so far! You could make one of those arbors with the flat spot on them that uses a small dowel to cam the piece tight. Using this, Use some Emery and sand the hot cap to a shiny finish.
> 
> Wes


That's a good idea.. I'll remember that come 'bling' time-- I tend to bang the parts around a little while I'm building, so I don't do much finishing until late in the game.


----------



## shred (Jan 20, 2008)

Made the bearing standards a couple days ago. Pretty straightforward cutouts, leaving just a little stock to ream for the bearings. The plans were a little vague on some of the contours, so I made up some that looked right. Later on once I determine the need for the holes I may go back and redo them with some fancier contours. 

I spent a while contemplating how to do the workholding to cut them out before I came to my senses and realized the finished parts were only an inch across-- slap some 1.5" flat in the vice and say 'go'... 

Bearing standards and the rest of the assembly so far: 
	

	
	
		
		

		
		
	


	




I also made my first try at the cold end cap today. The milling went great.. until I realized I had only left myself .085" to grip for turning the next .115" into a boss. I think I'll try that again in reverse order. Lathe first, then mill.


----------



## Powder keg (Jan 20, 2008)

Good Idea on leaving some to ream out on the bearing holes. I'll do that on my LTD that I'm planing:O)

Great job so far! Sometimes it's easer to "finish" the part buy emerying it down, before you part it off. Also I've noticed that shiny parts don't scratch up as easily as ones that are just lathe turned. Just something to think about?

Wes


----------



## shred (Jan 21, 2008)

Yesterday I built version 2 of the cold cap (the first scrapped part so far, not including a few fin-practice bits). Here it is with the bearing standards attached using overly-long SHCS (the loose screws are what hold the cold cap to the displacer cold end):






After the learning experience from the first part, it was pretty straightforward, though with a bunch of operations for a little part-- put a short bar end of 1.5" Aluminum round in the lathe, turn the .624 boss, ream the gland hole, skim the bar then move the bar over to the mill vice, get centered on it (using the above "edge-find the vice & use the centered v-notch" setup-- the previous skim cut keeps things aligned if the lathe chuck was off center or the original stock was non-round), and mill around four sides of the round to make the end into 1" square. Back to the lathe (or bandsaw) to part that off, then back to the mill the other way up to cut one of the central notches, rotate 90' and cut the other and drill the first four 2-56 holes. Flip it onto one side to drill, tap and cut the notch for the bearing standards, then flip and do the other side.

No doubt the entire process would be easier done with 1" square stock, but I had none in the bin, and plenty of 1.5" round.

(Aside: 1.5" round can make 1" square stock with a tad to spare. Remember your nemesis Pythagoras from middle school? The diagonal of a rectangle with sides of length A and B? A squared + B squared = C squared. Grab the shop calculator, add 1" squared to 1" squared, which equals 2, and take the square root. That's 1.414... So the diagonal of a 1" square fits in a 1.5" circle.. perfect. The easiest way I found to actually cut this is was to get centered on the round, then move half the length of the sides of the square plus the mill diameter (in this case 0.5 in both X and Y, plus the diameter, then drive the mill around in a square with sides of length 0.5+mill diameter. The same concept works for arbitrary rectangles as well.)

Looking back on it now, I'm thinking the Moriya and even more so, the posted Hot Air Engine plans, are simpler in regards to the cold cap and the bearing standards. Were I to do it again, I'd probably rescale one of those designs instead of using this one. I'm getting a little tired of tapping 2-56, and I'm sure tolerance stack errors are creeping in.

Here's the parts so far, more or less how they're supposed to be assembled:





One important milestone: completion of the cold cap completes the parts from the first page of the plans. Only two more pages to go.

[note; my server which hosts the pictures is acting up. If you don't see anything, try again in a ten minutes or so]


----------



## shred (Jan 22, 2008)

Today's part was the displacer piston body. Pretty straightforward conversion of solid rod into 1/32" wall tubing. I elected to make the bottom integral to the body instead of a separate part, so I did the bore-too-deep-and-face-back-to-depth trick again. A DRO would render such shenanigans moot, but I've yet resisted the idea of putting a DRO onto a circa 1938 lathe.






After the displacer is completed, I have to sort out what to do about the stand. I'll probably go with something closer to Moriya than Jerry's plans.


----------



## 1Kenny (Jan 22, 2008)

Its looking real nice, Shred.

Kenny


----------



## Powder keg (Jan 22, 2008)

That is starting to look Awesome!!! You are doing a great job! Keep the pictures coming:O)

Wes


----------



## shred (Jan 22, 2008)

Remember what Uncle Marv said in another post "if you scrap a part, take a break and don't try to make it again the same day" ???

Last night a couple different ways to salvage the first cold cap came to me. Making a second one didn't take that much time, but it's a good lesson to pay heed to (and one I've ignored previously)-- if you make a scrap part, break a tap, whatever, stop right then, put it down and just think about it for a while. Sometimes the first mistake can be fixed, but the next hasty attempts to repair it can't.


----------



## shred (Jan 24, 2008)

Quick update: Not much happening in the past few days; real life is attempting to intrude.. oh well, that's why it's a hobby and not a job.

I did get around to making the displacer top, over-drilling the precision 0.0625 press-fit hole, and patching it by using some .068 brass wire the hobby shop had. Brass isn't great when the aim is to be as light as possible, but it's not that different from steel and the next steel size up they had was 3/32". If all else fails I'll make a new displacer top.

I also started in on the crankshaft parts, making the crank pins and disks-- they're going to need some finishing work since contouring the outsides with the mill didn't turn out as nice as I'd like. I won't be able to loctite up the crank until I get some parts from page 3 made anyway.

Amazingly enough, the only parts left on page 2 are a couple cut-to-fit gaskets, the power piston, fan blades and spider (and I have a different plan for the latter two). That means I've got close to half the parts complete.


----------



## Powder keg (Jan 27, 2008)

Here's something to give you a little push:O)

[ame]http://www.youtube.com/watch?v=QvGbrM8RgYY&feature=related[/ame]

Wes


----------



## shred (Jan 27, 2008)

Other activities have been taking me away from the shop, but since the last installment, I designed and built the fan blades, spider and spinner, plus finished the power piston.

The power piston I made out of the end of my cylinder polishing mandrel. It was just the right size on the OD already and fits nicely. 

I'm pretty happy how the fan turned out especially since I didn't really like either plan. I got the design for the fan blades from an 1898 patent that the Emerson fan company used a version of until the 30's. A little late for the heyday of the stirling fan, but not too bad and it looks much more interesting than the usual fan. At this point I'm not planning to guard the blades, so the shape may also help with that.

Somehow in what must be ascribed to leaving the cap off the acetone, my design needed twelve more 2-56 tapped holes  :

The spinner was made by roughing at increasing angles in the lathe, followed by blending with a file. The four holes in the nose are extensions of the spider mounting screw holes, drilled through for the "nose-cannon" effect.

The blades themselves were cut from a brass door-plate-- a local hardware store is going out of business and at 75% off, kick plates are a bargain for brass sheet.






"Hokey Smoke Bullwinkle! They turned you into a fan!"

"Yeah Rock, I'm feeling pretty cool"


----------



## Powder keg (Jan 27, 2008)

That is beautifull!!! I like how it's coming together. 

Wes


----------



## Brass_Machine (Jan 27, 2008)

Wow Shred. I am dully impressed with those fan blades. Very stylin'


And yes I am old enough to know who Rocky and Bullwinkle are ;D

Eric


----------



## shred (Feb 4, 2008)

While the weather kept me out of the shop most of the weekend, I did get some small parts made:






Mostly rod-ends of various sorts. The two con rod ends on the right were interesting to make. I cross-drilled and profiled them in the mill on the end of some 1/4" brass rod using a collet block, then moved the rod to the lathe to drill/ream the 1/16" hole in the long end. I then parted them off, and super-glued the newly drilled hole onto a little mandrel-- a length of 3/16" drill rod with .100 of the end turned down to 1/16". Rechucking the drill rod, I drilled the oil cups in the other end of the part. A quick heat with a torch afterwards and the superglue comes right off.

Why 3/16" drill rod? I had just used that earlier to super-glue the crankshaft parts on to clean them up as well.

Here's a fuzzy picture of the setup. The ersatz tailstock DRO is just a caliper and a couple very strong magnets standing in until I chop it down and bolt it on for real (note how it barely clears the handwheel)


----------



## Powder keg (Feb 4, 2008)

Lookin good!!! I like Updates:O) Those parts turned out nice!!!

Wes


----------



## shred (Feb 7, 2008)

Major milestone. All the machined parts are done. "some assembly required".  ;D






All I need to do now is make some gaskets, pins and a raft of cut-down screws to hold it all together.

I did try the pin-vise itty bitty hole drilling method on one of the .050" holes just to try it and it worked amazingly well.


----------



## Powder keg (Feb 9, 2008)

What are you going to use for a gasket for the hot cap?

Wes


----------



## shred (Feb 9, 2008)

Powder keg  said:
			
		

> What are you going to use for a gasket for the hot cap?
> 
> Wes


The instructions call for some auto exhaust gasket material, but the drawings call out fiberfrax. I checked a couple auto parts stores and they only had pre-cut gaskets, which I could cut them from, but there would be a lot of waste. I happen to have some 1/8" fiberfrax (aka: kiln fiber paper) in my glass fusing supplies, so I'm going to try that. It's good to 1900'F, so that should be enough 

We'll see today.. I started final assembly last night.


----------



## Powder keg (Feb 9, 2008)

Where can you get Fiberfrax?

Good luck on your engine:O) I can't wait to see it run. 

Wes


----------



## shred (Feb 9, 2008)

Powder keg  said:
			
		

> Where can you get Fiberfrax?
> 
> Good luck on your engine:O) I can't wait to see it run.
> 
> Wes


Glass fusing shops (pottery/stained-glass artist supply). Ask for fiber paper:

http://www.homemodelenginemachinist.com/index.php?topic=1334.msg9636;topicseen#new


----------



## Powder keg (Feb 9, 2008)

Thanks!!!

Wes


----------



## shred (Feb 10, 2008)

Update: It's all together, but it doesn't run . Time to go chase down air leaks and friction points. Meh.

I ended up using auto gasket material because the Fiberfrax didn't stay together where I needed it. Mr Gasket "ultra" is a royal PITA to work-- it's got a layer of steel mesh through it, so scissors and X-acto knife are out. The drill press grabs and rips it apart. Small drills get knocked off alignment by the mesh.. I finally had to resort to the mill and a 1/16" end mill at 10K RPM just to get some half-decent gaskets, and they still look like a 2-year old hacked them out with blunt scissors.


----------



## Powder keg (Feb 10, 2008)

It'll Run Shred!!! Keep after it:O) Maybe a punch of some sort would make a nicer gasket? Just a thought. 

Good luck, Wes


----------



## shred (Feb 11, 2008)

It runs now! Needs some tuning and break in still, but it's going. Pictures and video will be along.

I had most of the problems in the book-- too much friction (those blasted gaskets again.. moving around), an air leak around the cold cap and I went ahead and re-made the piston in graphite, which helped a lot (I found some solid graphite 12mm pencils at an art store last week... after I'd made the piston from Al), as well as reducing the internal volume a little and pretty much tweaking on most every part. I'm on my 3rd or 4th crank pin by now-- I keep losing the things and making new ones is quicker than searching the muck under my bench.

If you had a big hydraulic setup a punch would be the way to go on the gaskets, but it'll take a lot of push. Either that or get the kind which isn't steel-reinforced to begin with.


----------



## Brass_Machine (Feb 11, 2008)

Waiting for the pictures and videos. ;D

Eric


----------



## shred (Feb 11, 2008)

Here ya go.. 

I should get some better ones soon, once it gets cleaned up some.


----------



## Powder keg (Feb 11, 2008)

That looks super!!! I can't wait to see the video:O)

Later, Wes


----------



## Brass_Machine (Feb 11, 2008)

That looks brilliant. Nice job. 

Eric


----------



## BobWarfield (Feb 11, 2008)

Yay, Shred, glad you got it running!

I'm wondering whether nicely machined surfaces and something like Permatex Ultra Copper High Temp RTV would have gotten you there for the gasket? It would seal, but perhaps would conduct too much heat across the gap.

Best,

BW


----------



## shred (Feb 11, 2008)

The main gasket issue in this design they're expected to add 1/8" or so of height to the displacer cylinder while keeping dead airspace to a minimum plus block heat from the hot cap sneaking around in the metal versus doing work; thus the fiberfrax wasn't strong enough to be used as a structural element. Were I to build another of these, I'd look hard at something different for heat-blocking-- either different gasket material, or a different design with thinner gasketing-- maybe a sandwich of stainless steel and thin fiber paper or something (Senft likes compressed asbestos material in the Moriya design, but I'm thinking that's a little hard to come by as well these days)


----------



## Brass_Machine (Feb 11, 2008)

Shred,

Still waiting for the video.... Get on with it! ;D

J/K

Eric


----------



## Powder keg (Feb 11, 2008)

Your killing us man....... We need Video:O)


----------



## tattoomike68 (Feb 12, 2008)

A video would be nice...


----------



## shred (Feb 13, 2008)

OK, here's some video.. of a sort, anyway.. Blair Witch has nothing on this camera work.. 

[youtube=425,350]UiXhCixraUA[/youtube]
Video 

View attachment SmallSterlingFan.wmv


----------



## Brass_Machine (Feb 13, 2008)

Bout time! looks good!

Eric


----------



## shred (Feb 13, 2008)

Yeah, it needs some cleanup and a proper lamp and stand, but it'll do for the time being


----------



## Powder keg (Feb 17, 2008)

Looks like it runs pretty good. Did it have many bugs to work out? I am going to build one of those after my LTD is done. I'll even probably steal some of your ideas:O) Thanks for the video!

Later, Wes


----------



## shred (Feb 17, 2008)

Powder keg  said:
			
		

> Looks like it runs pretty good. Did it have many bugs to work out? I am going to build one of those after my LTD is done. I'll even probably steal some of your ideas:O) Thanks for the video!
> 
> Later, Wes


Nothing too bad. A few of the plans weren't clear in spots which can cause some interference issues later on, but most of the debug was just fixing some air leaks and friction points. Should be a piece of cake after getting an LTD to run-- Tough to use a propane torch to encourage those to turn over 

I've got a lot of the milled & drilled parts drawn as simple DXF's, though they're designed for my little mill, so I don't know how useful they'd be otherwise.


----------



## Powder keg (Feb 17, 2008)

You have any plans for a lamp? A suggestion if you want a glass burner is to go to an antique or thrift store and look at old glass salt and pepper shakers. It would be easy to make a new top to hold a wick for one of those?

Make sure you post some pictures after cleanup:O)

Wes


----------



## shred (Feb 18, 2008)

My current lamp is an old Testorstm model paint jar-- one of the tiny glass ones-- I think the label is still on it in the video.  I made a little aluminum neck to hold the wick. One day I'll find a nicer jar, or turn one up out of brass or something, but this one works well for now.


----------

