# a rather unspectacular stirling engine...



## kutzdibutz (May 21, 2012)

Hi folks,

2nd project of mine is a stirling engine. One that I once built during an internship at university, where I was allowed for the simple parts. When it was coming to the crucial components the workshop master tapped me on the shoulder saying 'step aside lad, playtime is over, now its important'. And honestly- if he wouldnt have done so, I would have had no chance to finish this those days. (there was only a couple of days left for this)
So the piston, cylinder and fire tube the master did. And watching him do the stuff was very interesting. The flywheel, rods and the small stuff I did myself. But 100% self made is different... Anyways, I was proud like hell when I assembled it and it was running. 







That was the old days. Now having an own workshop I had to re-do this of course. I stayed with the basic design, however modified the plan slightly. The cooling ribs I choose to machine, the piston diameter I increased so it would fit the material I had and I would only need to cut the length (so I thought) and the flywheel design I changed also to the material available. The build proceeded and eventually I was done.










BUT: that bloody thing didn't run! (of course)

During machining of the cylinder I carefully watched the progress. The tool was cutting the brass nicely but at the final diameter I checked with the piston. I was still a bit tight so I choose to just have another go without feeding but this was already too much! Too much play of piston and cylinder and naturally the sealing was more than poor... :wall:

So I didn't want to spend the effort of making a new piston and no new cylinder either. Instead I made some PTFE piston rings. So the sealing definitely improved, but now the friction was way to high. Next to that issue the mechanics had some blockage which I removed by taking off the 'intersecting' material. But still, a no runner... Even though I tried to loop it and thought it would run reasonably smooth the friction increased again when heating up, since PTFE as a higher expansion rate than the other material (brass and steel). 

With this I had the stirling sitting for a while and did some long needed machine maintenance and modifications. Done that I came back to the stirling. (there was enough time in between to be motivated again do deal with it) After the unsuccessful attempt with the PTFE and several other fails trying to squeeze the piston to gain some diameter by deformation or trying to create some burr (silly me...) it became fairly obvious that its time for a new piston. So disassembly time...






First try, settings of the newly installed DRO wrong by 1mm, and it ended up off dimension- and of course too thin... (Murphy, you bastard!! :rant: )






2nd try, correct settings and there it is- left: the old bugger, right: the new guy.






The looping in setup: ('misused' the mill a bit)






and the final product







So while having the Stirling disassembled it was time to think about an upgrade and performance improvement:


















Some fan cooling should do the job... But first it should run at all... (which it still didnt- neither with nor without the fan)
With the new piston it was smoothly turning, no blockages in the mechanics, reasonably good sealing, not too much friction, correct timing. In other words- no reasonable excuse not to run... And heating it up one could see it wanted to- but there was some sort of lack of energy...
Some head-scratching later I realised I increased the piston diameter and consequently also the displacement piston. BUT: Apparently I should also have payed attention to the V-O-L-U-M-E increase of the displacement piston. I didnt start the big mathematics but made the 'extension' fitting to the room available. 














Assemble, fire it up and bingo- we got ourselves a runner!











However the self proclaimed performance upgrade consumes more than it delivers. So there is clearly room for improvement and plans are flying around in my head. 
Another huge improvement potential is the overall design, which turned out way more bulky than acceptable at the end. Mental note: get rid of all the bent and soldered sheet metal and make something proper. But at the moment time is rare- so lets see when there will be an update on that one.

Cheers, Karsten


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## kvom (May 21, 2012)

They're all spectacular when running. well done.


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## lazylathe (May 21, 2012)

Nice work Karsten! ;D

Now sound a lot of time reducing as much of the friction as you can
and try and get it to run on the least amount of heat possible.
That is always fun! :big:
With a bit of luck you may have it running of a tea light!

Andrew


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## mklotz (May 21, 2012)

Congratulations on a runner.

Is that displacer chamber made of brass? If so, it will be wicking a lot of the heat away quickly - not what you want. If you do another rebuild try making the chamber of steel, which doesn't conduct as well.


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## Troutsqueezer (May 21, 2012)

Nice write up, good pictures, very entertaining. Just what we like to see around here.


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## rake60 (May 21, 2012)

I see nothing unspectacular about it.

Nice Build! Thm:

Rick


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## Rockytime (May 21, 2012)

A great looking build. The machining looks excellent. I especially appreciate the flywheel.


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## rhitee93 (May 21, 2012)

Any running stirling is spectacular. Nice job Thm:


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## AussieJimG (May 22, 2012)

Well done and congratulations. They grow like Topsy when you try to improve them but you learn a lot on the way.
Thanks for sharing the journey and the photos.
Jim


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## kutzdibutz (May 23, 2012)

Thanks guys for the nice words. Some more mental notes taken... 
(Your comments clearly motivate moving forward)

Cheers, Karsten


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## AssassinXCV (May 23, 2012)

That sure is one solid flywheel. No wobble that I can tell from the video; or is that just the angle? :big: 
Looks like it's got some real power in it!

Ian


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## kutzdibutz (Jun 26, 2012)

Hi folks,

just a very quick update- some pics of the recent design work. This is how I intend the crank drive to look like:









Currently I'm really short on workshop-time but I look forward to flying metal chips- eventually... (hopefully soon)

For the main body I also have sketches ready but no 3D nor proper drawings yet. Showing real metal will anyway be more neat... 


Ian: the trick was to drill the center bore last, so the wobble is on the hub and not so well visible. 

So long-

Cheers, Karsten


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## kutzdibutz (Jul 25, 2012)

Hi folks,

still only virtual updates since the workshop is hardly operable at the moment and time is just absorbed by higher priority tasks... But some CAD is still possible every now and then. So this is what I have in mind for the stirling to look like:














I intend to use ball bearings but I didnt bother to model them- so it will not include a levitating shaft. 

Cheers, Karsten


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## Heatherrose (Jul 25, 2012)

Oh shoot! I was so looking forward to seeing the mag-lev bearing design.


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## MarioM (Jul 27, 2012)

I like to see it running.  Good work

Mario


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## Runner (Aug 5, 2012)

Hi Karsten, it was your thread that got me interested in the Stirling engine and the problems you had in getting it to run. I had to resort to Wikipedia to understand the priciple of operation. It appears that reducing the friction of moving parts goes towards getting the model to run. Your first two models have smaller (lower mass) connecting rods and the journals are a similar size to the crankshaft. However, your CAD design appears to have a beefier connecting rod and both journals appear bigger than the crankshaft, which would increase the force required to turn the engine. Am I wrong in my analysis and that you purposely made these bigger than your original for engineering reasons that I haven't realised?

Thanks for posting, I am following with interest.

Brian


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## kutzdibutz (Aug 5, 2012)

Hi Brian,
now you mention the mass of the connecting rods I start to wonder if my re-design is really such a good idea. But maybe I get away with it since I intend to use aluminum for the rods now, the bent sheet metal was steel. However there will be a slight increase of the mass. (which I try to compensate with the balancing weights on the crankshaft as good as it is possible- the initial design had none and the engine is shaking quite a bit when running, so I hope to improve that...)
Your observation of the increased size of journals is well spotted, and the conclusion you draw I can go along with. What is difficult to see in the CAD pictures is the ball bearings I will use for the connecting rods. So I had to increase the diameter to fit them. 
Thanks for your interest and following along.
Cheers, Karsten


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## kutzdibutz (Aug 5, 2012)

Hi folks,

finally I can declare my new workshop as back in operation after the move. Got my tool-wall newly installed, so this will hopefully help me not messing the place up so quickly... 





And there is also some progress to report! woohoo1
It was quite an effort and took some chest-hair to cut the piece of aluminum out of the bigger plate I fished out of a scrap bin once. (dont have a band saw or anything machine for the more rough cuts- so hand-saw...) On top thats really soft aluminum, so not really pleasant to machine as well. But thats the stuff I have, so I will live with that. First off cleaning the edges to have a proper reference for line marking:










Now I really see why some of you guys use this fancy looking paint... I need to get some... ;D

All marked up on the mill and finding '0', followed by the first holes:










Then step by step carving out the geometry...




















That worked ok so far, the two parts of the main body are joined by an M4 bolt and using 4mm positioning pins. 
Here's the rear side of the pilot hole for the main bearings. I started with 4mm, increased to 10mm- but that's how nice this material machines... (quite an excessive burr on the rear side) 





I left it with the cut out for the flywheel started:





Actually I'm quite happy with the progress- lets see when I get to it next time..

So long,
Karsten


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## kutzdibutz (Aug 13, 2012)

Hi folks,

made it to get some more machining done...
The cutout for the flywheel I did by perforation drill and then mill. I cleared the surface then with the end mill.












Next up there was rounding the two edges. I couldnt think of an easy way of aligning the parts on the rotary table so I followed a hint of a friend and used some washers for guidance and a file. Job done in 5min vs. two days of headscratching... 












Next up was the bearing section and machining of the outer radii. Again I had no idea how to properly put this on the rotary table so I made myself a small jig. The pilot hole for the bearing fits right on the pin and is secured by the washer and screw on top. So it can be turned by hand- feeding like the hedgehogs (how does a hedgehog have sex? - VERY careful!! ;D ) and only cutting against the mill rotation worked quite ok.

















Last step wil be widening the bearing holes to a snug fit with the bearings before this part can be ticked off as done. Hopefully I dont mess that up...

Cheers, Karsten


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## kutzdibutz (Aug 13, 2012)

So the first parts became reality! Last bit missing was the bearing holes. First I needed to 'find' the center of the hole after properly clamping the piece. I mounted both parts of the main body in order to drill the holes in one go. To find the center I used the dial indicator mounted in the mills spindle and adjusting x and y until there was no change in the reading rotating the spindle.












Once I found the center I locked the x and y axis and started boring the bearing holes:






Again feeding only tiny bits for two reasons- 1) not to over-shoot and 2) to get a nice surface. So the holes came out quite nice. One is acceptig the bearing willingly- maybe a tiny-whiny bit loose, but nothing loctite cant fix. The other hole turned out a bit tight, I should have gone through with the same feed once more... But gently pressing it in when I'm done with all the surface finish will do I guess... 







So I declare the first two parts as done. (the surface finish I will do for all parts in one go- I thought of sanding the parts to give them the 'as cast' look) 
I'm sure there would be better ways of machining them- so feel free to leave some remarks. 

Cheers, Karsten


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## kutzdibutz (Sep 21, 2012)

Hi there,
hmm- is there something wrong with the posts? Too many pictures? Too much bullsh*tting?, Too boring? Looks a bit like monologise around here... 
Anyways- I made it to the shop again and started the next part. This one will connect the power piston with the crankshaft. (eventually) Sketching it in CAD was sooo easy and quickly done- but making it for real took me some headscratching. First I cleared a piece of aluminum (of the same mavellous smearing sh*t) and placed in the 4-jaw. Center drill and turned the front bit round. 







For the ange of the cone I 'adjusted' the cutter- and of course it did  chatter like hell when it was cutting on the long edge of the tool. I  also know I should have used the cross slide adjusted to the cone angle-  but I was too lazy to take the support apart for back and forth adjustment and dismount all the chip  protection I installed for my DRO only to do a proper setup for making  the cone... At the end I removed the chatter-marks with a file. Not very elegant- but it worked... :hDe:






Then drilling the hole and the lathe job for this part is done...






So thats as far as I made it tonight- next fun will be on the mill again... 

Cheers, Karsten


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## kutzdibutz (Oct 6, 2012)

Hi there,
the last week I was doing bits and pieces on the main rod:
















During the milling operation the entire front end bent- not really surprising but I didnt think of that before... (didnt support the overhanging bit that bent) Luckily that was not such a big deal since I could straighten it by just bending the tip back. I put the tap into the M3 holes for indication how much to bend. (lay it flat on the indexing surface and bend the tip until the shaft of the tap is aligned with the angle bracket) That worked fine so far and the part actually starts to look like on the drawing. ;D






[...]







Sooo- today I intended to finish the main rod. There were only some - one would say - easy milling operations to do but I choose to mess the part up with the very first! :rant:






I dont know, but somehow I have the feeling that it might be of advantage to read the own drawing and actually follow it... Or make the drawing clearer... I picked the wrong dimension so the lower milled radius is 2mm off measure. The upper one would be the correct position... I think I mentioned that already somewhen- I would really appreciate if someone would invent 'metal-on-milling'!! 

Right, off to the scrap bin with this one and start over again. At least the new main rod attempt turned out a bit nicer so far. This time it didnt chatter so much making the cone. Maybe because I trimmed the blank a bit closer to the final dimension of the part. Or I clamped it a bit better- dont know...






Hopefully I manage to pick the measures correct now... Lets see...

So long
Karsten


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## Brian Rupnow (Oct 6, 2012)

Karsten---What a great thread!!! Somehow I had missed it before tonight. -----Brian


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## lathe nut (Oct 6, 2012)

Karsten, no, no, don't the photo's there is never to many, its great for someone who don't know how to make some of those cuts, thanks for the extra trouble to photo, Lathe Nut


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## ProdEng (Oct 7, 2012)

Karsten, I find marking out a workpiece helps avoid machining the wrong part away.  Even when I use the dials to place the cut there is always a line there to confirm.  Marking out takes a while, but once you are used to the process, not too long.

Watching parts emerge from the solid is always fun so keep posting the pics


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## kutzdibutz (Oct 15, 2012)

Hi folks,

thanks for the comments- this always gives some motivational boost!
@ProdEng: yes, I really have to get this into me, that so makes sense to have markings. I kind of skipped it mainly because I didnt think of that but also- at least for a small fraction- to move on. Where this can end up becomes quite obvious... 

So and while I was silent around here I was busy somewhere else. At least for the time I could spare. 
This time I changed the sequence a bit to avoid the bending of the front bit. I machined everything of the fork thingy that connects to the piston later on. So here we are ready to mess up again...





And guess what- this time it worked allright, because I payed extra attention... And there are even some lines I put by coincidence, because this was before I recieved the hint.. ;D






Next up I milled the pocket needed as clearance for the displacer rod. So I set it up with an angle of 10°. With the result I'm only moderately happy- I did nicer cuts before... But this is 'inside' the rod and will be barely visible when running.











For cleaning off the excess material along the shaft of the rod I used some mill shafts, a parallel and some blue loctite for the setup. The parallel I removed once clamped in the chuck.






Milling the 'ring' around the bearing I had some mishap again. I was doing a too enthusiastic cut and the part was ripped of the pin and bent the rear part all over. The idea of a photo was lost inbetween the swearing, grabbing the hammer and whacking it back into shape. So the bore for the bearing was not round anymore and also too wide. After a short cofferoom discussion with a friend the solution was more or less clear. Gently gently pressing the ring at 3 locations should give a snug fit for the bearing again. So give it a shot...






That worked, the bearing is now sitting tight again. 
Final touch was the radii on the fork thingy- this I did with a bit of patience by hand. Deemed it too risky machining that...






So thats it, part done. Pheeww....

Cheers, Karsten

PS: the displacer rod is also finished, I will sum that up a little later (today maybe, or tomorrow...)


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## kutzdibutz (Oct 15, 2012)

Hey there,

for the displacer rod I started off with a squared blank again. First the holes for the bearing and the conneciton pin and then milling the rough shape:











Then flipping it over and getting the rear side to the required measure.
















Milling the ring for the bearing I was much more careful and that worked. One side of the angled part I could mill quite easy, for the opposite bit I couldnt really clamp it in the vise. It wasnt sooo much, so I filed it.






Finally there was only the reduction at the front bit left and again filing the dradius. Too delicate for me and machining, and too fast and easy done by hand...






So there it is- finished parts are always nice, especially when they look pretty much as intended...  And slowly its coming together...











So thats all I can report so far. Next up will be the crankshaft stuff. Looking forward to it.

Cheers, Karsten


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## kutzdibutz (Oct 22, 2012)

Hi there again,

some collective update from the last couple of working sessions. 
I was a bit fast in saying that it would be down to the crankshaft yet... First there was another piece to be attached to the main body:





Holes for the positioning pins and in the center the M4 tap.






Next I properly clamped the piece on the mill and machined the two radii.
(still need to get a proper pen or paint for better visibility of the markings...)





After that I drilled the starting hole where the cylinder will be sitting later and rounded off the outer contour.





There were times where my fingers were dangeroulsy close to the fast spinning mill. Definetly out of my comfort zone but I proceeded with the awareness of the extra extra attention to be paid during this operation. I got away with it allright but would be grateful if someone has a hint how to make such things in a safer way. :hDe:

Next was the bore for the cylinder. So I found the center with the dial indicator on the outer contour. Then slowly and patiently increasing the diameter step by step. 











Done that there was disassembly time again to salvage the parts to be re-used. I really wondered why the heck I soldered the cylinder THAT well to the holder... Too much for the small lighter torch but no problem for the bigger one.  






So here we have the collection of scrap material:





The re-use:





And the new parts so far:





Next will be some small parts to connect the rods to the piston and displacer and then finally the crankshaft... 

Cheers, Karsten


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## kutzdibutz (Oct 28, 2012)

oh boy- just spent hours and hours realising how presistant and unforgiving little machining imperfections are when it comes to a nice and even suface finish... :wall:
So my fingers were getting silver while filing and sanding the aluminum parts. An the annoying bit- its not done yet. Still some way to go, quite done with the file, but more time to be spent with the fine grit... (where is that smiley with the beard growing??)

Cheers, Karsten


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## ProdEng (Oct 29, 2012)

A few hours spent filing and sanding will certainly help you to get a better machined surface next time, it worked for me !!!


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## kutzdibutz (Oct 30, 2012)

ProdEng said:


> A few hours spent filing and sanding will  certainly help you to get a better machined surface next time, it worked  for me !!!




LOL!! So true Jan! Definetly taught me a lesson- if I actually learned enough by this I'll see at the next try...


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## kutzdibutz (Nov 1, 2012)

Hi,

so the work with the file took again longer than expected. I thought I was done but then spent another evening... But it was worth it. Not only is the result better, but it also gave me enough time to get the idea to ask around in our material lab at work if I could sandblast the parts. That shortened the one or two evenings with filthy hands and sand paper to 15min during lunchbreak at the sandblaster! Generally I would be happy with the surface finish if it wouldnt be so damn scratch-sensitive. Even only putting it in the basket for US-cleaning left some marks! Also the water left some traces on the nice and clean surface... 





So next try will be glass bead blasting which I would have preferred anyway because it wouldnt leave that sharp and pointy peaks on the surface (looking microscopic) but rather smoother dents. Plus it compresses the very outer layer slightly. I just have to be patient enough to wait for the next meeting I have at the site where I could do this. (already phoned the guy in charge  )

In between I will take care about the small parts and the crankshaft- finished the drawings today.

Cheers, Karsten


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## kutzdibutz (Nov 13, 2012)

Hi folks,

in the mean time I did some small parts. The connection 'bolts' for the main rod are quite tiny. And I thought to myself- careful with the feed... lol






2nd try worked better, but I messed up again trying to cut the screwdriver slits by hand. Even with my thinnest Dremel-disk I was grinding the entire thing down and the groove was nowhere near usable. 






FAIL- repeat...

This time I milled the slits- that worked better. Using some cut off aluminum as soft brackets, and the final product:











Now thats acceptable... 

So long
Karsten


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## kutzdibutz (Nov 13, 2012)

Hi, 

next on the list is the crankshaft. In order not to produce an excessive amount of swarf I gave it a shot soldering the shaft. More or less 1st try but if one never starts, one never will manage that... :
So I prepared the shaft and a bigger hunk of material which later form the two crank disks. 






I used some white flux, brass solder and two torches but the attempt sort of failed. The pieces sticked together somehowbut the wetting of the joint was really poor. It survived the parting of the two disks on the lathe, but cleaning the disk connected to the shaft was too much. The joint gave in. There was still enough force to keep the parts together- way enough for the power of the stirling, but I wanted it better, so next try:






Ready for fore again






The result was moderate again. No wetting through and also no nice fillet.











And I was melting the solder quite well. The brass was liquid, but was somehow refusing to flow into that gap... Some web research left me with the suspicion, brass solder is not really the way to go. Soldering temperature of 800-1000°C is quite a call... I will get silver solder, around 600°C is more do-able. So I guess the flux was burnt before the brass was liquid... Anyway, the piece survived the cleaning on the lathe, good enough for the later requirements to the part...











And here we have another good example why marking the part is quite a good idea- one hole again on the wrong side of the center line. FAIL- repeat. I will learn this eventually... :hDe:






Now thats better:






to be continued...


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## kutzdibutz (Nov 13, 2012)

back again, I broke up the post to imit the number of pictures...

The center hole in parts I use for proper referencing on the machine as well as mounting guide. The holes are reamed to 4mm and I use a positioning pin later for alignment during machining.
















So here we have the parts of the crankshaft:






And assembled with the locking pins bolted in:











So I'm quite happy with that- not far from assembly time! 

Cheers, Karsten


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## kutzdibutz (Nov 14, 2012)

woohoo1
Sometimes paitience is payed off! Today I could get access to this glass bead blasting thing and I'm really happy with the result. Silky-smooth surface- excellent! For once I'm not ashamed of close-ups... 











And woohoo1 again- assembly has officially started!! I'm so curious if everything will fit together as intended... 






Just didnt have the time to assemble everything today. So far it is quite balanced out, bit heavy on the flywheel side. There is the pistons and fire tube missing. I will go mental if it happens to be fully balanced when complete. That would be just too much of a coincidence. ;D (didnt really pay attention to that detail during design...)

Cheers, Karsten


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## Rocketcaver (Nov 30, 2012)

Beautiful work!


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## kutzdibutz (Dec 21, 2012)

thanks rocketcaver.

Hi folks,

time for an update again... A quite long frustration found an end. During assembly I noticed a minor resistance in the movement of the displacer piston connecting bar. Having had a closer look to the bore through the piston I realised it was not perfect- it had some weird burr inside. So I reamed it to the next diameter which meant I would need a new connecting bar again. And this sucker provided me with some extra grey hair! It ended up too thin and convex but cylindrical and all in different attempts. On top the switch of my grinder was broken and I was running out of sharp tools... (explaining the convex shape) :rant:
Long story short- it took 5 (FIVE!!) attempts to finish this bit!





The assembly of the piston and rod was also a bit fiddly and needed some furhter de-burring. But nothing too dramatic.





Trying to fit the piston in the cylinder it became apparent that pressing the cylinder into the holder it did something to the dimension of the cylinder itself. So another go looping the part in... 





But eventually I got so far to have piston and rods assembled.





BUT: 
I do not know and cant really explain what made think I would only need the pocket for displacer rod clearance on the one side of the main rod... :wall:





Yes, clearance is also needed on the other half of the revolution... ts ts ts... Assumptions during design lead to rework. 

And there is also some clash that stops a full revolution at the connection of the displacer rod. 





Fixed both in the mean time- but now I need to go for glass beads once more... 

So long
Karsten


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## starnovice (Dec 21, 2012)

Very educational post.  Thanks for sharing your mistakes and how you fixed them.  Great work!

Pat


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## kutzdibutz (Dec 22, 2012)

Thanks Pat, I don't mean to be educational- it's just my two penny worth...
(but maybe its the sometimes trial and error that adds some flavour  )

haha- and talking of errors- did it again... When looking at the 'freed up space' at the piston I realised I was a bit enthusiastic and also freed up most of the hole the piston connects with the rod... There was some material left but very thin and even though a stirling has not that massive power with time that could give in. So I drilled that hole a bit bigger and pressed some brass bushings in. now there is more contact surface for the connection pin to the rod. 





And looking at the milled pocket at the rod I decided to skip the effort running around for glass beads- I didn't do much damage to the other surfaces and at the end it doesnt look too bad...





So I also finished the displacer pushrod to fit the displacer itself. All the movement is free in the revolution. There is only the firetube to be mounted but workshop time was more than up... Plus I want to swap it with a stainless steel version for heat conductivity reason (following a recommendation from the beginning of this thread). Lets see how this machines, otherwise I'll keep the brass version...





So happy holidays everyone!
Cheers, Karsten


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## kutzdibutz (Dec 23, 2012)

Hey there, 

couldnt resist to assemble in between and fire it up...
And it runs- not that big surprise since I re-used most of the running parts, but its still nice to see. At the end I'm quite happy with the balancing, as well with the dynamic balancing... 
The little dinging happens when the displacer hits the end of the firetube. So there will be a little bit more room with the stainless steel firetube I'm on.
(sorry for the crappy video- one more hand would be helpful...)





http://s1056.photobucket.com/albums/t370/kutzdibutz/stirling/?action=view¤t=IMG_1311.mp4

Cheers, Karsten


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## Brian Rupnow (Dec 23, 2012)

Excellent work!!! I was setting back in the bush with heavy doubts---It looked too heavy to run. It appears to run great. CONGRATULATIONS!!!


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## starnovice (Dec 24, 2012)

Well done Karsen!  I really like your decision to use glass beads.  I notice it has a built in governor. If it runs too fast it turns away from the flame to slow down 

Pat


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## kutzdibutz (Dec 24, 2012)

Thanks guys! 

Brian, completely out of curiosity- at what point / which part did you expect too heavy for it to run? The piston and displacer I re-used, so no weight added, the rods (especially the main rod) look a bit beefier, but they are made from aluminum, so not that much added weight either. Havnt directly compared them to the 'origina' parts, but I guess its about break even. The parts with the massive weight added is the crankshaft and I did this intentionally in order to have a chance to compensate the reciprocal piston movement. (which works reasonably well- could be done better for sure, but I'm quite happy with the result)

And Pat- well spotted, well spotted... 

Laters
Karsten


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## Brian Rupnow (Dec 24, 2012)

About post #19 and #20 I was thnking "Too much mass".--Parts look to heavy for a Stirling engine. Then again, I have never built a Stirling engine. Most of the ones I have seen on this forum are rather delicate, fragile looking things. Your's looks like it could be used to pull stumps.


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## kutzdibutz (Dec 24, 2012)

Hmm- #19 and #20 are the body parts. Correct me if I'm wrong, but to my oppinion they could be as heavy as they like and it still would run as long as the moving bits dont get too heavy. There I think its a matter of taste if one likes elegant or sturdy. Obviously I'm more the sturdy-type, mainly because I judge my machining skills as too clumsy... ;D (or I want to keep it simple if possible)

Cheers, Karsten


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## Tin Falcon (Dec 24, 2012)

Karsten the tille of the thread does not do justice to the engine. the engine looks great. looking through the posts it does look like a lot of redesign and remaking of frame parts. but I love the end result. 
Tin


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## kutzdibutz (Dec 24, 2012)

Thanks Tin,
the title of the thread aims more at the initial stiling with all that bent metal- and 'that thing' before the re-design looked rather crappy... And it was about that time of starting the tread I got the idea about doing something to the looks of the stirling. Nowdays I would maybe name it different but thats how things grow and they still have the same name... 

So 'Stage 1' of the makeover is almost completed, 'Stage 2' will include a actual working performance upgrade. (a cooling fan that actually adds some net power output, not only spins and consumes more than it delivers) But there I first need to get into CAD a bit more again...

Cheers, Karsten


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## kutzdibutz (Dec 30, 2012)

So ladies and gents,

machining the stainless firetube I thought- this better be key... But at the end it worked quite allright. Startet with the bore to the desired depth, then the outer contour and parting at the right location. 











hands filthy, part shiny- thats how its supposed to be!





Used some grinding paper for a nice smooth surface finish just before parting. The frietube has a wall thickness of 0.3mm, further I didnt want to push it (sissy me...) and the stainless really works well- the heat doesnt travel as into the 'cold' part as with the brass. Nice hint Marv (mklotz).

Mounted the stirling on the very temporary base plate and officially declare stage1 of the re-make completed.





And I also made a bit nicer video of it running...
http://s1056.photobucket.com/albums/t370/kutzdibutz/stirling/?action=view¤t=stirlingre-makestage1complete.mp4

As said already- next up will be  an actually working performance kit, a proper burner and a nice baseplate. So CAD again for a change...

Cheers, Karsten


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## kutzdibutz (Jan 1, 2013)

Hmm- big question mark poppingup. After some fiddling around in CAD I'm not so sure about the cooling fan anymore. Somehow the proporions look a bit ridiculous... Side view of the fan housing- I could reduce the outer diameter slightly but not too much really.





The housing I dont want to skip. I want some guidance of the flow and better fan efficiency. Here some other view of the desaster... (havnt bothered to model the fan blades and guide vanes yet). 










There should also be a connection piece to the cooling ribs. Couldnt figure out how to model that yet- its a bit of a weird shape with the transition from round crossection to rectangular following the outer diameter of the ribs...

I would really be looking forward to designing the blade and vane angles and then make the stuff but at the moment I'm 50/50 between do it or not do it at all... scratch.gif

Any inputs and ideas welcome and highly appreciated!

Cheers, Karsten


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## kutzdibutz (Jan 11, 2013)

Hi all,

had some time to think about that 'upgrade kit' with the cooling fan and stuff. Some headscratching and a measurement later it becomes more or less apparent to me that the fan installation is not only looking pretty silly but there is also no big benefit to expect. The stirling lives off the temperature difference between the hot and cold part. One could maintain a sufficient temperature delta by 
a) having a good and focussed heat source on the hot side
b) take the heat away as good as possible on the cold side
c) stop the heat from travelling from hot to cold (or better say hinder the travel as much as possible, it cant really be stopped)

a) I need to work on, there is no question. 
c) is fairly well considered thanks to the recommendation to change the material of the fire tube. Next to that I introduced another seal so its not too easy for the heat to travel.  
Concerning b) I thought a fan would assist the cooling. Which it would for sure. But looking at the actual situation with the stirling in operation I would guess the hot part to have app. 500°C, the firetube starts to glow in a dark red. And the cooling ribs I can touch without burning my fingers. Thats when suspicion started to grow if a fan would help or not. So I measured the temperature of the cooling ribs and they are at app. 50-60°C. So there is a temperature delta of around 400K. With the fan I could maybe gain another 20-30K but thats not that impressive compared to the 400K available and a fan would need to be powered... So with that in mind I will skip the fan- and it also tells me that c) works reasonably well. 8)  

So next thing will be a proper burner.

Cheers, Karsten


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## kutzdibutz (Jan 20, 2013)

Hi folks,

so this weekend I had a friend coming along and we did some speed measurements. Max speed measured was 1250rpm! Relly pleased with that!

In the meantime I must have lost my motivation to make a nice burner and base plate... If someone spots my motivation- please direct it back to me otherwise I will struggle to really finish that project... 
One other thing, I'm thinking of a consumer for the stirling- preferrably something pretty stupid and useless... But so far only a water fountain came to my mind. Hmm- lets see if I get a better idea. Any suggestions?

Cheers Karsten


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## JaamieG (Jan 21, 2013)

Very nice and neat construction. I really like it.
I am planning to build a Stirling as soon I have finalised the 2-stroke motor.
Good inspiration.
Cheers,
Giacomo


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## franscubitt (Feb 4, 2013)

Hi Karsten
in your lovely build, is the joint of the Hot cylindar to the cold side there to provide a thermal brake?
I have built severall Stirlings but none a pretty as yours and have not yet used a thermal break although common sence tells me it
should help a lot?
Cheers Frans


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## kutzdibutz (Feb 5, 2013)

Thanks Giacomo.

Frans,
yes, the flange works as thermal barrier and yes, I think it is key. Having said that it doesnt mean a stirling wouldnt work without that... But as I mentioned in the post on top of this page you can do two things- b) and c) and if you do c) reasonably well you can skip certain things at b). Thats where I decided to skip the cooling fan. 
The thermal barrier in my design works like this: (the weird hatch represents insulation material, in my case PTFE)





Cheers, Karsten


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## franscubitt (Feb 7, 2013)

Thanks very much,
I am trying to develop a low power Stirling made from an oil barell that can be made by Poorer communitys for lighting ect so at present making a crude small scale test 10W Stirling so I really appreciate your answer.
Cheers Frans


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