Author Topic: Brass Stirling (#3) (Read 22824 times)

cidrontmg · « **on:** December 15, 2010, 04:11:19 PM »

Hi, after 9 days without Net. Our house was (once again) hit by a lightning bolt, Monday 6th, and it (as usual) burned the cable modem, router, etc. Today we got it repaired, the telecom people had to change >200 m of cable also, and everything connected to it. We have had a wireless LAN here for some years, just because lightning bolts are a once-twice yearly thing, so no computers were hit this time. It´s been "silent" here, Net-wise, and TV-wise... Good opportunity for starting (and almost finishing) another Stirling engine...

I didn´t take many pictures, but some. The engine will look a lot like this.

This is an image from "Maschinen im Modellbau", Jan. 2003, and as you can see, there´s just a drawing without any measures. And some pictures of the finished thing. Not a construction article at all. In fact, that´s the entire story you see. I hope this doesn´t come too close to breaking copyright. Anyway, I like the design, and will try to do something similar.
I have some test tubes to use for something, so they will determine the size, +/-. The rest of the materials will be all brass, except the crank and piston shafts, ball bearings and some fasteners. Many of the screws will also be brass.
Starting with the displacer cylinder (cooler), and the heads. This will be a small engine, the hex brass is 30 mm across flats, and the head fixing screws are M2X7 and M2x9.5.

And here´s the test tube as it will sit on the cylinder.

Bearing support and the flywheel(s). You may have seen the flywheel in the other Stirling build pictures. Since then, I´ve drilled some holes in it, and turned away the crank disk.

Parts for the base. The base plate will be much wider than in the drawing, because I had this brass bit in the junk. The base pillar will also be bored to be the work cylinder.

And the base together. Cylinder not yet bored.

And one more of the displacer cylinder with the test tube attachment ring.

So, that´s for today. More tomorrow, if there´s no lightning strikes again...

madjackghengis · « **Reply #1 on:** December 15, 2010, 07:43:07 PM »

Hi Olli, that looks like a very similar design as the Robinson, but but with the displacer and power piston reversed, but with same method of offsetting the two by 90 degrees. It looks like it will probably be pretty efficient, and a good runner. I'm looking forward to seeing it finished and running. Sorry about the lightning strike, hope you get everything straightened out from it.

mad jack

NickG · « **Reply #2 on:** December 16, 2010, 03:24:41 AM »

Nice engine Olli, you've really got the bug for these stirlings now!!!

Stilldrillin · « **Reply #3 on:** December 16, 2010, 03:49:38 AM »

Looking good Olli!

Never seen that drawing before. As Jack says, it's very much a twisted around, Robinson!

Don't like the sound of the regular lightning bolts.....

Keep safe, stay happy!

David D

arnoldb · « **Reply #4 on:** December 16, 2010, 12:12:14 PM »

That's a really nice start Olli

From the sound of things, you should consider a lightening powered engine

, Arnold

crabsign69 · « **Reply #5 on:** December 16, 2010, 01:10:02 PM »

Quote from: arnoldb on December 16, 2010, 12:12:14 PM

That's a really nice start Olli

From the sound of things, you should consider a lightening powered engine

, Arnold

I was just about to say that too. U beat me to it. hahahaha nice

cidrontmg · « **Reply #6 on:** December 16, 2010, 10:40:09 PM »

Quote from: NickG on December 16, 2010, 03:24:41 AM

Nice engine Olli, you've really got the bug for these stirlings now!!!

Heh, yes. Like I told in the other thread, I bought 4 small test tubes, to have something to practice with, in case I break a few, but then I didn´t, and there are still 3 ready-cut tubes to find a use for. Here goes one, and I´ll keep the other two for spares. They WILL be broken some day.

Quote from: arnoldb on December 16, 2010, 12:12:14 PM

From the sound of things, you should consider a lightening powered engine

Arnold

Ehh, ok, considered. The answer is NO. I emphatically hate lightning bolts. In Finland, I used to have a 30 m high (well earthed) tower for ham radio antennas, and there I got one hit. I wasn´t operating the rig at the time (of course, or I couldn´t be writing this...), but home all the same. I did NOT like the experience.

I considered building another similar tower here, but after the first winter thunderstorms, I preferred to live a little bit longer.
And an engine which may start for a few milliseconds, maybe once or twice a year, and hopefully when there´s no one around to see it, doesn´t sound like my thing...

Yes, indeed, it looks (and acts) like a Robinson Stirling. That also means that it will run in the opposite direction to the two previous engines. Those run so that the flywheel top moves away from the cylinders. This thing should run so that the flywheel top moves towards the cylinders.
Once again, I did a mock up, to get some measures for the next parts.

And made the parts. The displacer piston rod is not yet to length, I´ll cut it later when I have the displacer made. I´m planning on using a small ball bearing (from an old hard drive) to attach the power piston rod to the "balance" arm. I also made a small nipple to connect the plastic tube to the power cylinder.

And bored the power cylinder and made a piston. It´s a blind hole, so it cannot be reamed. I let the boring bar (thickest I have) run several times slowly through the bore without advancing, until it didn´t shave even dust any more from the bore. The piston is a 7.2 mm ali bar which is pushed to a 7 mm hole in the Teflon bar. No need to glue it, I don´t think I could get it apart without breaking anything. When the air from the hole in the PTFE has been pushed away, there´s an almost perfect vacuum holding the pieces together, if you try to pull them apart. And of course the ali "heart" will stiffen the Teflon for turning it into size. The cylinder bore is 13.7 mm, that seemed like "enough". The engine in the drawing has a 12 mm cylinder. This engine will have a shorter stroke, however.

There´s also need for a tapped hole in the cylinder side, to let the pressure in. And BTW, it is an excellent idea, NOT to push the piston all the way down in the cylinder, before drilling this hole. It can be a real PITA to get it out, if it´s a reasonable fit (and especially if it´s a bit too tight... Don´t ask me how I know...). With the hole, you can blow it out. In the drawing, the said hole is rather high from the cylinder bottom, I´d prefer to have as little "dead" air space as possible in the cylinder. There´s more than enough in the connecting tube anyway. So my hole goes to the small cone that is an artifact from the drill, from boring the initial hole.

The piston entering the cylinder. I am holding the tube plugged, and it won´t enter any more. If I let loose of the tube, it will start descending, and hit the bottom some 25-30 sec later. It may be too snug, but that´s easily remedied.

And another mock up. The power piston rod has no big end yet, it´s just tied to the balance arm. As you can see, the power piston and the displacer are not aligned, as in the drawing. The drawing has a double power piston rod, that goes on both sides of the displacer rod. That might be a good idea, but I´m trying to get away with just one rod. It will need either a better guidance in the balance arm, or a little more slop to compensate. Of course I´ll try first the slop...

The displacer proper once again seems problematic. I still don´t have suitable ali tubing, or any smaller test tubes (as in the drawing). And I don´t think I have any suitable electrolytes either, this time. Brass tube might be one possibility,but I´ll figure out something.
That´s about the size of things as of writing, there might be some days before I come up with the displacer.
Thanks for all the comments, much appreciated!

Stilldrillin · « **Reply #7 on:** December 17, 2010, 02:10:18 AM »

Olli.
Only one comment...... They're beautiful parts you've made!

I'm sure it will run just as good as it looks.....

David D

NickG · « **Reply #8 on:** December 17, 2010, 03:33:49 AM »

Couple of comments -

@ putting piston in cylinder before air hole was there - I thought only I did stupid

things !!!

Again, like me, you can't resist mock ups - I had the flywheel balancing on top of my tiny stirling!

Looking good, that fit on the piston is easlily good enough.

Nick

cidrontmg · « **Reply #9 on:** December 18, 2010, 08:48:27 PM »

Some more. I think this might work as a displacer. 18 mm stainless tube is easily available here. Not only in DIY supermarkets, but there are lots of wine piping makers who use it. In Finland, it was known as "dairy tube", here it is "winery tube", but same stuff, thin-walled (0.7 mm) stainless. I got lots of 30-50 cm cutoffs for free from a wine tank maker. I made press fit end caps from ali, and the first one was short.

I don´t know what happened, but it´s not usable. OK, good practice anyway, and I made another that was certainly long enough, initially... It is well known that shortening to length is far easier than the other way round...

A problem immediately appeared when I then attached it to the rod, and tried how it would move. Very poorly. I had been planning to use an all-ali displacer, which obviously would have been a lot lighter. I turned the tube to 17.5 mm, still heavy. 17.3 mm, and rather heavy even so. Another 0.1 mm away, not looking much better. Hrm. There´s only 0.3 mm left of the tube walls...
Enough with thinning the tube. I´ll have to make another cylinder cover, which has a longer hole for better guidance for the rod. There is room inside the cylinder, but it won´t be enough. The spigot must also be longer. That means the displacer rod must also be longer, with a shorter joint to the crank...

What must be, must be, so I made another cover, displ. piston rod, and the joint. New parts here, in situ. As the new cylinder cover is also a bit thicker, there´s plenty of room to sink the screw heads. I think you already have noticed that I like sunk screw heads...

If done "correctly" (like in a Swiss watch, or a good shotgun), the screwdriver slots should also all point to the same direction (up, so any dirt falls better off). So you would need to pair every screw to its respective hole. Well, I´m not THAT correct...

And then I tweaked the displacer length so that it will almost bottom at both ends, but not quite. It comes close to the glass cylinder, but without touching it.

Now it seems to be moving rather happily. The next things will be the power piston big end, and a hole with a nipple for the plastic tube in the displacer cylinder. Then it should be in running order, that is, all parts made at least for the first time.

arnoldb · « **Reply #10 on:** December 19, 2010, 03:03:00 AM »

Nice going Olli

I don't blame you for not wanting to have anything to do with lightening - Had my own close call with it about 14 years ago... Was outside and just felt all my hair starting to raise... Hit the deck and it hit a tree about 15m away from me. I keep inside when there's thunder in the air now, and still prefer fiberglass fishing rods to graphite compound ones.

, Arnold

sbwhart · « **Reply #11 on:** December 19, 2010, 03:14:00 AM »

You're making a real nice job of that engine Ollie

can't wait for the video of it running.

Stew

NickG · « **Reply #12 on:** December 19, 2010, 03:53:54 AM »

Olli, I've never thought that about CSk screws before but you're right, they do look classy. Good luck hope to see another runner very soon then

madjackghengis · « **Reply #13 on:** December 19, 2010, 09:45:31 AM »

Hi Olli, looks like you're moving right along with the next stirling, and things looking up with that thin stainless. "And bored the power cylinder and made a piston. It´s a blind hole, so it cannot be reamed. I let the boring bar (thickest I have) run several times slowly through the bore without advancing, until it didn´t shave even dust any more from the bore. The piston is a 7.2 mm ali bar which is pushed to a 7 mm hole in the Teflon bar. No need to glue it, I don´t think I could get it apart without breaking anything. When the air from the hole in the PTFE has been pushed away, there´s an almost perfect vacuum holding the pieces together, if you try to pull them apart. And of course the ali "heart" will stiffen the Teflon for turning it into size. The cylinder bore is 13.7 mm, that seemed like "enough". The engine in the drawing has a 12 mm cylinder. This engine will have a shorter stroke, however." I took the quote, only to say, as long as you don't bottom out the power piston, the bore can be reamed, and in situations such as yours, I've reamed a cylinder and then carefully run a boring bar to the point where the reamer's taper starts, and bored out that bottom little bit, getting perhaps an extra half a thousandths clearance for that little bit, but not affecting the compression significantly at all. My lathe has a tendency of getting swarf under the rear flat way, and goes from turning straight to a slight taper without warning, if I don't specifically clean out that way and under the back of the cross slide, so I use reamers for cylinders when possible, but with the DRO, I can move a boring tool right down to the end of the reamed part, and make the cut through just the part of the taper of a machine reamer while avoiding touching any of the reamed area. By the way, I'd be inclined to use a piece of copper tube, say eighth inch or so, for the line between displacer and power cylinders, and solder it, just to be sure its airtight with minimum dead space.

mad jack

picclock · « **Reply #14 on:** December 19, 2010, 05:20:41 PM »

Hi Ollie

Really nice work there - and if the finishes are as good as the camera makes them look, it will be quite a stunner.

However, a slight word of caution (just call me Doctor Doom). PTFE is a fickle material when it gets warm

. It has a high coefficient of expansion and gets very floppy.

I used it in a temperature controlled oven once for testing TV Triplers for export to the Emerates. And despite using 3/8 inch thick material ran into significant issues. An easy check would be to put your piston/cylinder assembly on a radiator or in an oven to check for fit when its warmed up. I hope I'm wrong about this but .. .

Look forward to seeing it running.

Best Regards

picclock

cidrontmg · « **Reply #15 on:** December 19, 2010, 07:07:18 PM »

Hi Mad Jack, right you are in that a blind bore can be reamed. Another thing is, if it´s worth while. In this case, it´s a short cylinder, 1.4", and the piston stroke is only +/- 6 mm (1/4"), from the bottom. That means the piston crown would work entirely in the conical area of the reamed bore. I think it´s easier and faster to just bore all the way, if you must bore it anyway for the bottom part. Saves one setup!
About the copper/brass connecting tube - I´ve also been seriously considering that. Not only would it be tighter (if done well...), it also would not be flexible, like a plastic tube, which will expand and shrink with pressure variations. I realize it won´t flex much with the pressures we´re talking about, so it´s more theoretical. And plastic tube does work in practice. But even so, in comparison to a metal tube, it will flex many times more, and we´re talking about very small pressure variations. Any flexing is power lost. Another thing would be the looks. A brass tube wins hands down. I don´t like the looks of plastic tubes in small steam/Stirling engines, they seem cheap, and out of place, and temporary (add any other derogatory adjectives here). The only snag in using a brass tube is, it would probably need two junctions, and it is very short, an L with 10 x 20 mm legs. One alternative would be to soft solder it in place... This needs some more consideration, but I´m fairly sure that I´ll make a brass tube before even trying it for running.

Hi picclock, yes indeed, Teflon and heat/steam don´t mix well. I´ve heard about (never did myself) PTFE pistons in steam engines, and they can be made to work, but it´s not very straightforward. I wouldn´t even bother with a Teflon piston in an I.C. engine. Gamma type Stirlings however are "different" beasts in the sense that the work cylinder/piston never gets hot, usually not even warm (and if it does, there´s a grave design fault...). In this particular design, the cylinder is quite massive, and bolted to the thinnish base plate. The base plate admittedly also carries the displacer cylinder, which will heat it somewhat. But I fully expect that after even a longish run (1/2 hour), the work cylinder will be only modestly warm. Should that prove not to be the case, I will mount the cylinder to an ali plate. Next step would be this.

Otherwise, it goes to a wooden base board.

Brass is nice to work with, it will polish relatively easily, and stay that way, for a while at least. And it can be blackened also easily, I am considering blackening the displacer cylinder. It would also slightly help with cooling, but of course it would be more for the looks. And maybe also blacken the screws. Here (almost) properly aligned.

I guess I will blacken a few, see how they would look.

cidrontmg · « **Reply #16 on:** December 24, 2010, 10:26:55 AM »

Fat lady sings again. A picture of her with many swinging arms.

I also did a video, technically awful, shaky hands and poor eyesight. But the essential is there

She needs quite a bit of pre-warming, but then runs and runs. One lamp fill of spirits will keep her happy for some 40 minutes. These machines seem to need longish run-in periods, they pick up more speed the longer you run them. Common to many other engines. But she runs quite happily as it is.

I´ll post a few more pictures after it´s blinged and cleaned a bit. For now, a clunky Stirling for Christmas bells

It is mounted to a piece of Chinese bamboo kitchen cutting board...
Thanks for watching, everyone, and a merry Christmas (if you celebrate it).

madjackghengis · « **Reply #17 on:** December 24, 2010, 11:56:50 AM »

Hi Olli, good to see you get the engine running, it looks good and sounds very good, complete with real engine noise. I had suggested the copper tube because of its smaller volume, and being able to soft solder it in place, "minimizing dead air", but you're right about expansion and its effects on efficiency. I take it you don't have to revert to a heat sink and can use the wood base you'd planned. All in all, a fine engine, and I think I will have to emulate this one. I found a smallish cigar tube in my tool box, it's been there for a couple of decades, but I just found a piece of very thin walled stainless tube which is the right size to go with the cigar tube, and I like the style of your engine, so I think I will be making a similar one soon. Very nice all around, and a nice looking and sounding video as well.
Merry Christmas, and God Bless you in the Coming New Year. May God Bless us one and all. mad jack

Stilldrillin · « **Reply #18 on:** December 24, 2010, 12:18:24 PM »

Olli.
Yer've done it again!

You're making it look very easy now!

Wishing a Merry Christmas to you, and all MadModders, everywhere.....

David D

NickG · « **Reply #19 on:** December 24, 2010, 02:38:40 PM »

Really nice Olli, well done once again!

cidrontmg · « **Reply #20 on:** December 25, 2010, 02:43:44 PM »

No bling yet, but some more pictures. I´ve done a burner, and modified some bits. And I think I´ll do still some mods. It´s running better all the time, but I believe it´s not yet as good as it might be with little(?) additional mods.
The burner, not looking much as yet, but working, and no leaks.

One end cap is the same ex-displacer cylinder cover that I had to make new.

This is how it looks at this stage.

Something that is no longer visible. The displacer must have a vent hole. Here, 1 mm dia. It is otherwise rather dangerous (to the engine). It is an airtight chamber, which gets very hot. Without a vent hole, it will build quite a pressure inside, and maybe pop one end cap away. And destroy the test tube. If you build something similar, keep in mind...

The tube that connects the cylinders. It is brass, and the displacer end is threaded 5/32X40, and screwed directly to the cylinder (with thread sealer). The other end has a normal tubing joint. The "back curve" is needed for the locking nut to move somewhat.

The displacer rod sealing seems to be a critical point in these engines. Once again there was an audible leak in there, so I made a Teflon bushing. Now it is quite tight.

I cut two half moons off the crank disk, to balance things somewhat. In this type of engine, there are reciprocating masses moving at 90^o to each other, so balancing the crank so that it is "neutral" (=will stop at a random position) will not balance all of the engine. To my surprise, this mod was pretty effective. The engine vibrates very little.

I still will need to attend to the power piston big end. There´s a ball bearing there, but the structure is too heavy. It sits on top of the power piston, so any extra weight there is power wasted.
More when there´s more.

madjackghengis · « **Reply #21 on:** December 26, 2010, 09:26:40 PM »

Hi Olli, it looks like youre getting that stirling together very nicely. I always enjoy when an old piece, discarded, can be re-used, it feels like sort of organ donation engine to engine. I went back to get a better look at all the parts and pieces on your power piston, I got to thinking if you wanted, you could set up a spriing under the piston which comes close to counter balancing the static weight, and with that for rebound, you would get most of all that power back, you'd just keep the mass and the associated inertial loads and factors such as its most natural rpm. You've got so much mass involved in the direct movement of the power piston it probably wouldn't be as effective trying to substantially reduce the weight directly on the piston rod, although it could do fine with a plain bearing on a pin, given it doesn't rotate much in angular movement. Don't mean to criticize, just some thoughts from looking long and serious at that design, planning on building one of similar nature at some point soon. I think it's looking very sharp with the polishing up, and the matching burner done up. I enjoy the extraordinary number of moving levers and pieces.

well done, mad jack

arnoldb · « **Reply #22 on:** December 28, 2010, 10:40:14 AM »

Nice one Olli; runs like a charm

, Arnold

picclock · « **Reply #23 on:** January 04, 2011, 07:07:46 AM »

Hi Ollie

Very nice to see it running, it certainly looks the part in the video.

Glad to see that my predictions (and prejudices) with the PTFE (Teflon) piston expansion were unfounded.

Hope the rest of the year turns out as successfully for you.

Best Regards

picclock

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Author Topic: Brass Stirling (#3) (Read 22824 times)