MadModder
Gallery, Projects and General => Project Logs => Topic started by: cidrontmg on November 11, 2010, 10:59:09 PM
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Some time ago I built a Stirling engine, shown here http://madmodder.net/index.php?topic=3761.msg40590#msg40590
Since then Iīve mounted it to a base board, and it has been running for many hours (1/4 l of ethanol).
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Model.jpg)
It now runs so nice I thought Iīd build another, a bit bigger (about 1.3 scale) this time. Most of the materials will be similar, but Iīm out of 4 mm ali plate and 16x16 bar, so I will use brass for those parts. Iīve also bought the difficult items (test tube, graphite, bearings, fasteners, etc.), so letīs see how it goes. Thereīs no real plans for this, Iīm just making parts to fit together...
There should be a Stirling inside these.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/oma9.jpg)
And these
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/oma12.jpg)
The flywheel is just to keep the ali bars from rolling away, it wonīt be part of the engine. You will notice that I bought two test tubes, just in case. I didnīt break the tube for my first engine when cutting it, but I might, this time around... The test tubes are 30 mm dia outside, in the above engine itīs 20 mm. Thatīs nowhere near 1.3 scale, I know... But as any politician will tell you, thereīs never too much hot air... The cord in the picture is glass fibre, to be used as a wick for the spirit lamp. Thereīs 1 meter of it, enough for many, many lamps.
The graphite is a lump of 20 mm dia and 42 mm long, enough for 2 pistons at least. There are also 5 bearings (of 10x6x3 mm) in the bag, only 2 will be needed for this build.
I probably wonīt be making this in a hurry, so be patient...
:wave:
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Good luck Olli...... :wave:
I'll be patient! :thumbup:
David D
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Cutting the bars to size. I have a B&D band saw that I misuse for such things.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/oma31.jpg)
Cutting 4 mm brass is a piece of cake. About the same as cutting 6 mm plywood.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/oma33.jpg)
40 and 50 mm ali bars take some time, but far less than with a hacksaw. And way easier to my right shoulder.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/oma34.jpg)
I also cut the 16x16 mm brass, and some 70 mm ali, for the flywheel. Thatīs about the max. that the B&D will take.
There were 2 pieces of the 50x4 mm brass, 113 mm long, 2 pieces of 40 mm dia ali, 53 mm and 20 mm long, 2 pieces of 50 mm ali, 60 and 20 mm long, one 16x16 mm brass, 105 mm long, and one 70 mm dia ali, 18 mm long. Thatīs all the "big" pieces. There will be some smaller pieces also, but they will be salvaged from scrapped stuff. More later.
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Looking forward to watching this build :thumbup:
Rob
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Looking forward to watching this build :thumbup:
Rob
+1 :clap:
Cheers, John :thumbup:
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Looking forward to watching this build :thumbup:
Rob
+1 :clap:
Cheers, John :thumbup:
+2
Gonna like this one!
Eric
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Olli,
My little B&D bandsaw has been the backbone of my workshop for the last 25 years. I did make a pair of roller blade guides for it instead of the plastic ones, and it cuts all my non ferrous stuff without complaint, no matter how large. Just give it a new blade every so often and away it goes.
I am really going to enjoy this build.
Bogs
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Hi Olli, I've always wanted to build a Stirling with a glass tube for the displacer, I believe this will be the motivator to get me going on one. I'm looking forward to watching this build, and and gaining some insight into some of the things it entails. You're certainly off to a good start. mad jack
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Not much done today. Drilled the 16x16 mm bar that will serve as the bearing support. I cut the bar intentionally too long, I wasnīt sure how to make the seats for the ball bearings. Thereīs now an extra hole that will be cut away later, and thereīs still more than enough of it left...
The idea is to mount the bearings to the two sides of the 16x16, so it would be necessary for the seats to be in line, otherwise the crankshaft will not be at 90o to the rest of the engine.
I first tried to use a 5 mm counterbore drill. It supposedly leaves a 10 mm counterbore (the bearings are 10x6x3 mm).
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/oma24.jpg)
Well, the hole was actually 10.30 mm. Thatīs way too much slack to fill with Loctite. Next attempt was with a 10 mm end mill.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/oma26.jpg)
A lot better. The hole is 10.15 mm. Just about the ticket.
These small ball bearings (and anything even smaller, of course) are best treated with like a babyīs eye. Consider that the bearing thickness is just (10-6)/2 = 2 mm (0.0785"). In that space, there are the balls and the outer and inner races. The races are 0.5 mm (0.019") at their thickest. It doesnīt take much force to distort them. Especially the inner race is very easy to expand if the shaft is too thick or irregular. Itīs a very good idea to use silver steel (drill rod), but to my surprise I couldnīt find any 6 mm stock :bang:
OK, next best(?) would be stainless rod, itīs also reasonably even in thickness. As the Germans (from Joachim Steinkeīs page) say "Eine Passung, die nicht geschliffen ist, ist keine Passung", or, a fit that has not been ground, is not a fit. The shaft must be ground (with 800-1000 grit emery paper) to slide with very little force through the bearings. Not to drop through, of course. But if you rotate the shaft in the bearing, and it feels "gritty", itīs no good. Not because the bearing will be destroyed prematurely, as it will, but because these small engines donīt develop much power, and itīs silly to waste a lot of the little in the bearings. It can mean the difference between a good runner, and a non-runner.
I made a flywheel, ali, 70 mm dia and 16 mm wide. When mounted temporarily to the shaft, and given a hefty push (by a finger), it should turn for at the very least 10 sec. 15 sec is all OK, the engine wonīt be a non-runner because of the bearing losses. 20 sec and over is quite achievable. The more, the merrier.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/FW1.jpg)
I had another bronze flywheel, also 70 mm and 13.5 mm wide, made for an an engine for which it was too small. That much heavier flywheel will turn for over 30 sec.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/FW3.jpg)
But itīs probably too heavy, for high revs. Worth experimenting, though.
Thanks for watching!
:wave:
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Hi Olli, I enjoyed the bit of German lesson, I have immense respect for lots of aspects of German engineering and that quote is a good one. I was wondering what sort of aluminum you are going to be using for the power cylinder, assuming you will be using the graphite for the power piston. I have a kit for a single cylinder Stirling with power piston and displacer operating in the same cylinder, and Jerry Howell advises lining the aluminum with brass or using steel for the power cylinder, even with the graphite for a piston. My flame sucker has a habit of scoring the cylinder every half hour or so of running, requiring lapping out the cylinder, lapping the o.d. of the bronze piston with 600 grit paper, and lapping both the outside of the cylinder valve face, and the valve. I don't mind so much, but it tends to stick when I'm showing it to someone. I'm considering making a graphite piston and valve for it, but don't want to waste the time or the graphite if it's just going to be longer intervals, and still gall up. I've made two replacement cylinders, as the old ones get out of round, and tapered, along with a couple two or three replacement pistons as well, just to keep the little engine running in its original form. Have you run graphite as a piston in aluminum before? Always looking for more knowledge :poke: mad jack
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Hi mad jack, I wish I knew what sort of aluminium it is! The seller said it comes from France, and thatīs all he knew. Itīs probably something similar to 6061, very easy to machine anyway. In the other (smaller) machine, there are aluminiums from (at least) three different sources. The power cylinder is from a bar I bought in Hamburg, Germany, the flywheel is from the same local bought French bars, and the displacer cylinder is made from AFAIK a Norwegian bar bought from Sweden. None of the sellers knew much about their properties. They all machine quite well, and polish also well, but the French bars rapidly lose their lustre and turn dull. In the first picture, if you compare the power cylinder and the flywheel, you see what I mean. When I finished polishing them they were equally shiny. The effect is even stronger in nature than in the photos. The power piston is almost like chrome plated, the flywheel is like the bottom of a Coke can.
Iīve had a graphite piston in an ali cylinder in one engine before these two, a steam (= compressed air) engine. I think they work just fine - if the cylinders are rather cool, as they are with compressed or even hot air. I think even in a flame sucker the temperatures would be low enough. I have no experience about steam or I.C., and graphite/aluminium, and Iīm very skeptical until proven wrong :scratch:
Graphite doesnīt expand nearly as much with heat as aluminium (graphite=0.5-6.5 when aluminium=23.1), so if the cylinder gets quite hot, the graphite piston wonīt follow, and will start to leak. BTW, graphite is "two-directional", it has a laminar structure, like a stack of paper. The expansion across the stack is just 0.5, the 6.5 is along the "grain". A graphite bar is "amorphous", meaning that thereīs graphite particles in every direction. Usually in a graphite bar there are more particles oriented along the bar than across it. So the piston lengthens several times more than it grows in thickness, per every degree of temp. The ali cylinder would expand 46(!) times more with each degree, if all the graphite particles were oriented along the bar. Even if in fact theyīre not, a graphite piston wonīt expand practically at all with heat. So cylinders for graphite pistons should not get very hot, or they will start to leak, no matter what theyīre made of.
Steel has a thermal expansion coefficient of 12 (half that of ali), stainless is 17.2, and brass is about the same as aluminium at 20.3. Anything wonīt come even close to cross-grain graphite in that respect. Pure chromium, and certain glasses are near to amorphous graphite.
Another thing is that a graphite piston will slide freely in just about any cylinder material. It doesnīt much matter, if the cylinder is cool, what it is made of. Graphite will almost certainly be far softer anyway, and slightly scratch against the cylinder walls, and thus lubricate it. And you should never oil graphite. It will not make it more slippery, just the opposite. If you absolutely MUST lubricate a graphite piston, the only alternative is graphite powder :)
I guess Jerry Howellīs Stirling is so-called beta type, where both the pistons are in line. His recommendation is good in the sense that itīs easier(?) to replace a worn graphite piston than a cylinder. Of course thereīs wear in both, no matter how slippery graphite is, and in an aluminium cylinder, it would be worse. A steel liner would be far more wear resistant, and expand a little less with heat than ali. Also it would be a worse heat conductor, so it would remain cooler for longer, and expand less than ali. Iīm not so sure about using brass, it is harder than ali, of course, but just about as good a conductor of heat, and will expand just as much with it.
The flame sucker might benefit from a graphite piston. Theyīre notoriously hard to lubricate. A graphite piston would solve that. The problem would be keeping the "cold" end of the cylinder cool enough that the piston wonīt leak. If the piston is tight in the cold end, it will be sucked towards the flame (hotter) end, and there it would be more leaky. The flame (=hot gases) will get sucked inside even if it is, but it shouldnīt leak much near the bottom dead center. In my Stirling, there are two narrow grooves in the piston, theyīre trying to imitate a labyrinth seal. Not sure if they do anything useful really, but every little helps... And at the very least, the grooved piston weighs a little less... :D
:wave:
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Started with the cylinders, doing the cooling fins. First the displacer cyl.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/DCyl1.jpg)
continued with the work cyl. Thereīs lots of ali ribbon in the swarf bucket already...
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/WCyl1.jpg)
The original work cylinder has a blind bore, no separate head. Thatīs good against leaks, but doesnīt somehow look right... This time Iīll make a proper separate cylinder head, leaky or rather not, and make some fins there also. Cooling fins here are more for the looks, they donīt serve any useful purpose. Who cares. Just some more milling for aesthetics...
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/WCyltop1.jpg)
Then thereīs the piece that unites the glass cylinder with the displacer cyl. Thereīs of course a hole for the test tube. Starting the hole.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/DCyltop1.jpg)
The test tube is a nominal 30 mm, but in reality itīs 28.9 mm +/- 0.01. I bored the hole 29.3 mm, so thereīs 0.2 all around it. It must not be too snug a fit in the hole, or it is likely to develop a hairline crack. Seems to fit OK.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/DCyltop3.jpg)
Then thereīs the screw holes for fixing the heads. I plan to use similar M3 hex cylinder heads to the original. It has 4 holes, this time Iīll do 6. I also want to sink the screw heads somewhat. The heads are very concentric with the threads, and actually meant to be sunk, they provide some guidance to the piece to be fixed. Often they are not, thereīs not enough thickness in the piece, or theyīre left protruding because they enhance the "technological" appearance... Whatever, I first milled the screw head seats (6.5 mm), and then drilled the 3 mm holes.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/WCyltop3.jpg)
And hereīs todayīs catch. Not much, but thereīs a bucket of ribbony swarf at least.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Cyls1.jpg)
The O-ring in the middle is 30 mm outside dia. and 4 mm thick. This is how it will be around the tube when the engine is assembled. A little over half of it will be in the chamfer.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Testtube2.jpg)
More when thereīs more to show. Thanks for watching!
:wave:
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Hm. I forgot one picture thatīs rather relevant. "A little over half of it will be in the chamfer." What chamfer??
The chamfer is here.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/DCyltop2.jpg)
Done by turning the top slide to something like 40-50o, the angle is not very important, neither is the width of the chamfer, something like 5 mm. It will probably need some adjusting when the engine is assembled. The idea is that most of the O-ring will be inside the chamfer, and it will be pressed against the cylinder top. That way, it will seal the glass tube both along its side, and against the displacer cylinder.
:wave:
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Very nice work so far!
Anxious to see how you cut the test tube. When I tried it, I had disastrous results
Eric
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Beautiful work Olli! :clap:
David D
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Beautiful work Olli, and a very fine lesson on the structure of the graphite, I appreciate the fine detail you go into and will store it for the future. Your guess is right, regarding the Stirling being a beta type, and I will do a build log when I get to that project, and decide in the mean time, exactly how I will do the cylinder. I really want to cast it of bronze, having a good bit of scrap, but I have to practice my wood working techniques some as it's been some time since I had to put draft on patterns. In the mean time, I'm looking forward to seeing this engine you build come to be, and see it running. :bugeye: :whip: :poke: mad jack
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Yep, Lovely work Olli, I love stirling engines, will be watching closely!
Nick
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Not much done today, but something.
The two 50x4 mm brass platters will make the cylinder supports. I drilled plenty of holes to them and screwed them together and drew the center line. The cylinder centers will be 65 mm so I marked them, drew a couple of circles for the cylinder outlines and bolt holes, and drilled two M4 holes. I took some pictures, but managed to get them way off focus. I donīt much like the (Chinese) camera I recently bought, itīs really a camcorder, and does pretty awful stills. Min. focus seems to be about 50 cm... A new (Japanese) camera is on the way...
Anyway, I used the B&D to remove most of the excess brass, and put the platters into the rotab. And (slowly and carefully) milled the outlines of the cylinders. And drilled the fixing holes (M3 for the time being). An M4 cylinder head is not much to hold on in the chuck. But it went rather well.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/oma30.jpg)
And here they are still together.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/oma22.jpg)
I will use M4 screws to fix the cylinders, M3 seems rather skimpy. The cylinder central holes will need to be opened up quite a bit, and Iīll fly cut all the surfaces, although the brass stock was rather clean and not too scratched. But the brass might be a bit warped, and the sides that will go together when assembled, will need to be true and flat. And the platters are unnecessarily thick. Iīll use M4x16 stainless screws because I have a huge stock of them. The thread length in M4x16 is 12 mm, so it leaves just 4 mm to go in the cylinder. It would surely be enough, but if I fly cut 0.25 mm from each surface, it will be another mm, for the six screws. Certain is certain... :thumbup:
There will also be a milled channel in the middle of (at least) one of the pieces, to pass the air (pressure) between the cylinders. Thatīs for maybe tomorrow. Weather forecast is rain, time to stay indoors.
:wave:
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Nice work again olli. I think I am getting tool envy as it seems a great deal more can be achieved with rotary tables, I have to stick to basic shapes. I guess you still need experience and the right techniques though, if I tried it it would probably end up like a dogs dinner!
Nick
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Nothing done today, it didnīt rain as promised, and the new camera arrived. This thing (Canon SX20) focuses from 28 mm on. Thatīs practically touching the lens. Some learning curve ahead, it is a point-and-click, but thereīs lots of ways to make bad pictures even so. One sample that wasnīt a total failure.
:wave:
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Nice work!
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Nice work and great pic!
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Some more work done. Drilled some holes, tapped a little fewer, fly cut the brass pieces a bit thinner, scrounged the scrap bin for some more parts, tried some polishing (no real success, but the scratches show better), and mocked up what I have now. I need to measure and mark some lengths and distances from the assembled parts, so itīs not just for showing up. But thatīs the main reason, of course... :)
Cylinder heads in place.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Mock2.jpg)
Flywheel, again with 5 holes. The bottom plate started life as a CPU cooler from a scrapped computer. I sawed the fins away and fly cut the surface, leaving it slightly thicker in the middle, because the cooling fins were cut that way. Also thereīs a bit missing from the left corner. Thatīs not my doing, it (and the fin) was cut away already in the computer. Some electrolytes in the main board apparently came too close to comfort. I guess Iīll round the whole corner later on.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Mock3-1.jpg)
Taking shape.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Mock1.jpg)
There are some Sharpie marks in the cylinders+heads, to keep them always oriented the same way. Later on, they wonīt be needed. After the air passages are bored, the cylinders can be oriented just one way in the support. You might notice that the bearings will not go entirely in their milled cavities. Theyīre some 0.2 mm proud. Thatīs to make the distance between them as big as possible - every little helps, etc.
You also might notice that this engine will be a mirror image of the smaller model.
Have to take some measures now, or the rest of the parts wonīt fit together...
Thanks for watching, more in the pipeline.
:wave:
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Wow Olli That is coming along very quickly. Very impressive.
Eric
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Beautiful work Olli, I know how good it must be if it's showing up like that on close ups, the camera always makes stuff look worse than it is.
I can't work out where the air passages are going yet so I'll have to keep watching :lol:
Nick
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Some more. I rounded the base board corners. I donīt have a "proper" tool for this, so I took a wood router bit, it has carbide tips, so itīs all OK with aluminium. Took several passes, small chips everywhere... Ran the mill probably faster than at any time before.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Rounding4.jpg)
I also polished the board, tool marks and scratches incl. And the rest of the stand. They can now be put aside for a while.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Stand2.jpg)
Then it was about cutting the air passages in the cylinder supports. In the platter that goes next to the cylinders, there are two holes for passing the air to the cylinders, and a channel uniting the holes. In the other platter, thereīs just the channel. I used a bit of scrap ali to hold the platters in the mill vise. Drilled and tapped some M4 holes in the sacrificial bit, and attached the platter with some screws. And drilled the M4 (so far) holes.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Channel1.jpg)
And milled the channel
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Channel2.jpg)
Hereīs the two plates, and the ali "jig" to hold them.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Channel3.jpg)
The displacer cyl. will have a hole that aligns with this hole. It will go straight "up" to the bottom of the displacer cylinder. The hole for the power cylinder in the previous engine needed a bit more complications. There is a brass pipe that goes right through the cooling fins towards the cylinder top. There is a horizontal hole, bored into the cylinder top, that unites this pipe and the cylinder. And then the hole in the cylinder side was plugged with a small piece of ali. You can see the said pipe and the ali plug in the other engine, in here. Itīs sort of "hidden", not too obviously visible. But itīs there. :D
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Brasstube1.jpg)
In this engine, thereīs a separate cylinder head, so the brass pipe will pass right through along the whole cylinder, and also go some way into the head. And then Iīll mill a channel in the cyl. head to pass the air above the piston.
More when thereīs more
:wave:
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Thanks Olli, now I know how it works! :thumbup:
Nick
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Some more photos. I drilled the hole for the tubing alongside the power cylinder, and milled the hole in the cylinder head. The tubing end protrudes slightly into the head.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Tubing2.jpg)
Then thereīs need to open up the holes in the cylinder support plates for the power cylinder, to create space for the connecting rod. Not much space above the lathe ways, but enough. I drilled it to 20 mm. The piston will be 19 mm (cylinder bore = 19.05mm = 3/4"), so it can enter freely.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Lathe_boring1.jpg)
And then bored the cylinder to 18,5 mm, and opened it with a 3/4" reamer. I donīt have a drill chuck nearly big enough to hold 19 mm, but the reamer has a centre, so no big problem. You can see thereīs a homemade handle to facilitate turning the mandrel by hand, and slowly feeding with the tailstock, a lot of cutting oil, a spanner holding the reamer from turning, it worked quite well. The bore is straight, uniform in size, and with a rather good surface finish.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Ream2.jpg)
I had a slight change of plans. I was intending to use graphite for the power piston, but turning graphite is a messy business. The graphite bar is 20 mm dia, so about 1 mm needs to be turned to dust. Itīs not terribly much, but...
So I was thinking about a Teflon piston. Or rather a Teflon wrapper around an aluminium core. Teflon is also a very low friction material...
I turned an ali bar to 12 mm dia, 23 mm long, and made 10 mm deep hole with M4 thread into one end. And turned a 23 mm stump of Teflon to 19 mm dia, with a 12 mm hole in one end. And pressed the two together. Rummaging in my scrap bin, I found a 70 mm long 6x6 brass bar, and bingo! - a con rod. Unfortunately it was some 4.5 mm short...
I also found a bit of 13 mm bronze bar. I turned the bar to a nicer(?) shape, and milled a 6 mm slot in it.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Bigend1.jpg)
And soldered the two together.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Solder1.jpg)
Now the con rod is long enough. I made a small brass piece, 6 mm dia, with a M4 thread to go into the piston, and a flexible joint with the con rod. So thereīs the power piston as it now stands.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Pwrpiston2.jpg)
Thereīs a reddish tinge on the Teflon, donīt know why. But itīs really snow white. The bronze "big end" really is rather reddish, clearly different from the brass. I turned two thin grooves in the Teflon, and wound them full of plumberīs Teflon tape. Not that itīs really needed, the piston has a good compression even without it. But it seems to wipe away "something" from the cylinder bore, and it can be easily replaced. And the compression "fine tuned". The stroke is 20 mm, it will be the same also in the displacer cylinder.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Conrod2.jpg)
The power piston now breathes freely through the tubing, and with a hefty flick of a finger on the flywheel, it turns something like 22-23 revolutions (a bit difficult to count). If you block the tubing, it just bounces back and forth, not even one full rev. So thereīs still some hope - it hasnīt jammed solid yet...
:wave:
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Olli,
Nice work. I was wondering about the use of teflon for a piston but I bet it's more difficult to achieve a good fit than with graphite? I suppose the heat won't be (hopefully) much at the cold end so it should cope with that ok. It sounds like you've got a good seal but a high compression ratio - it shiould be a fast runner provided there's enough volume of air heated to overcome the compression, or rather you heat the air enough.
Nick
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Olli.
Some time back, I used PTFE for the 5/16" diameter pistons, in a special Mamod steam engine.
When the steam hit, they expanded by around .0025", jammed solid........ Modified, to a thinner PTFE sleeve, still gave .0015 expansion..... :doh:
I think you will have to experiment, even at Stirling temperatures...... :wave:
The experiment was a success....... The engine is still performing as hoped for, with it's new owner, in Australia. :thumbup:
David D
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Hi Stilldrillin, NickG,
I havenīt used PTFE for a piston before, so it well might not be a good idea, but still worth trying. I can revert back to the graphite (I still have it...) if itīs a no go! I just didnīt feel like turning graphite right then. I had other engagements that evening, and didnīt want to show up there looking like someone just rescued from a coal mine... Iīve turned graphite a couple of times, and it makes an awful mess. At least it did with me! :lol:
Experimenting is certainly in the books, thatīs the main reason for building this engine. I also want to experiment with other displacer sizes and materials. And balancing the engine, etc. Teflon and graphite, although both very low friction, are quite different as to thermal expansion. Graphite-not at all, PTFE-plenty. In this particular Stirling type, the work cylinder always stays cool, so I hope PTFE will behave. If not, too bad, and on to something else. :)
What Iīm worried about now is balancing the engine. That connecting rod is sturdy, but boy is it heavy! Drilling holes in it (or grooves) will make some difference, but Iīm afraid not nearly enough. Taking off some material from the crank disk will also make a bit of difference, but still not enough I think. Lead weights opposite the crank pin... Might be...
Thanks for watching, more on the way.
:wave:
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Not much. Did another flywheel to experiment with. Rather, it was an old brass flywheel that had an 8 mm hole. Too large, the crank axle is 6 mm. I guess I could have done a split taper fit, but it also had a smallish hub, nowhere near the +/- 22 mm needed (the engine will have a 20 mm stroke). So I made a plug, cut a 5 mm disk of 30 mm brass bar, and soldered them together. Then I cut two lobes away with a 2.25" face and side cutter (and didnīt take pictures :bang: )...
And then Loctited the plug in the flywheel (green goo in the picture). Itīs now waiting to harden, will drill and ream it tomorrow. And probably drill (again...) 5 holes to make it lighter.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/AltFW1.jpg)
:wave:
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Crisp work Olli! :clap: :thumbup:
Mine never looks so good....... ::)
David D
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A few bits more. I cut some glass. I first cut the flared portion off the test tube, to get a feel how it works. Not too well, seemingly, because I broke the flared end... This doesnīt seem to be genuine Schott glassware, although itīs branded as Duran. Or maybe Schott has a factory in China... So a bit more care, and another trial cut. I just need 78 mm from the bulb, and thereīs 200 mm of it. Better this time, but not good. One more cut, this time with feeling, at the right length. Third time lucky, seems like the real McCoy. The cutting tool is next to the pieces, a "Dremel" diamond disc, definitely made in ROC. This is still the first test tube, I bought two.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Glass1.jpg)
The tube needs a hole in the displacer cylinder, so it had to be bored to size. The piston rod is 6 mm, and now I have bought some more silver steel (drill rod), and there will be two Oilite bushings to guide and to seal it. The displacer will be some 25-26 mm dia, the glass tube is 27 mm inside, so the rest of the displacer must be bored also to 27 mm.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/DCylbore1.jpg)
There must also be a small step (+/- 10 mm long) for the test tube to enter, its outside is 29 mm.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/DCylbore2.jpg)
And enter it does.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/DCylbore3.jpg)
Test tube in place, with the O-ring, and a bit of silver steel with the bushings.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Glass3.jpg)
Bushings pressed into the displ. cylinder.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Bushing1.jpg)
And another mockup. Seems to be rather square and reasonably well aligned.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Mock8.jpg)
Itīs not missing much, the displacer proper and its connecting rod. Might run during the weekend. Or maybe not... :)
:wave:
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yep, nearly there Olli :thumbup: , I'm confident it'll run - your machining looks spot on.
Nick
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Hi Nick, that engine is really moving along, and should be running here, shortly. Cutting glass is always a bit dicey, I've had good success with thin tubes by wrapping a cotton string around and tying it off, then putting some lighter fluid on it and lighting it, and hitting it with some water when it is about burned out, cracking it off pretty cleanly where the string was. Some care with a propane torch, taking lots of time to heat up the edge evenly very slowly, and the edge can be melted to a nice round profile, and eliminating cracks from starting from an unfinished edge. I always practice on the throw away piece because I never can be patient enough until I've cracked on before sucess strikes. I'm wanting very much to find a couple of test tubes myself, with all this inspiration. That ought to be a fine running engine when you're done with it. :bugeye: :poke: mad jack
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Hi madjack, the way you suggested (with a "burning string") is also good. I cut the tubes for the previous engine that way. For the other engine, I bought 4 test tubes (showing great confidence in my glass cutting abilities..). I cut them all that way, all broke exactly where intended.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Tubes1.jpg)
Itīs also a very good idea to "polish" the cut edge with heating. Slowly is the key word, and careful... I overheated one of the tubes, and it instantly began to creep. See the left side on the pic below. Itīs not round anymore :bang:
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Tubes2.jpg)
The tube is usable, thereīs tolerance enough in the cyl. bore. But if it ever comes into contact with the ali cylinder wall, itīs fairly certain to crack. Borosilicate glass develops hairline cracks very easily, it doesnīt shatter to small pieces.
I went to cutting with a diamond disc, although the burning string method works very well. But I also wanted to try if I can cut an opening in the cylinder side. Havenīt tried that yet, but I will :D
Test tubes usually canīt be bought one off, they come in lots of 10-50. Not that it matters much, theyīre cheap(?) in bigger lots, and you often need more than one :) One source for single/a few tubes is
http://www.bengs-modellbau.com/material/buildingmaterials/index.php
theyīre in Germany, the same site in German http://www.bengs-modellbau.de/
the German site is far bigger. Good quality, lots of hard-to-get things, and they send very fast. No connection except a happy customer :thumbup:
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The end in sight. The only piece missing is the displacer, and that has caused some head scratching. Seems I donīt have (and canīt quickly arrange) 25-30 mm aluminium tubing. :bang:
So what else is there... Plastic - no. Wood - no. Some heavier metal - ehh, no... A cigar case would be just about ideal - except I donīt have one that big. Might need a Robusto- or even Gordito- size. I have some cigar tubes, but the biggest is 16 mm dia. Not nearly enough.
It is of course possible to make a tube from a solid piece of bar. Starting with a 30 mm, and making swarf and throwing away some 95% of it just doesnīt sound good. Hm. What comes nowadays in aluminium cases... Even many cigars come now in plastic tubes...
After rummaging through some accumulated and increasingly unlikely trash (it tends to accumulate...), I hit the jackpot. An electrolytic capacitor, quite old and most likely dried up years ago. Outside dia. = 25.5 mm. Hehe. Just what the doctor ordered.
So I opened it up, by turning a bit away in the lathe, and stripped it of its (dried up) innards. It turned out to have massive amounts of rock-hard asphalt inside. I cleaned it away with paint solvent, and got just about everything out, but it was a struggle. I then turned an end cap for it.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Elcap2.jpg)
British made even. And then glued the end cap in place with Loctite. And itīs a nice fit in the tube also.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Elcap3.jpg)
So tomorrow, Iīm going to finish it. I think Iīll wipe the texts away, and polish it slightly. Thereīs a few dents in it, but I hope it will do. At least until I get some bigger cigars in ali tubes. :)
Thereīs also the need for a bigger spirit lamp. Iīll first try, and hope it will work with the smaller engine lamp, but of course this engine needs its own. Back to scrounging the scrap buckets...
:wave:
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Hi Oli, that capacitor turned out to be a nice fit, and leaving the printing on it leaves something interesting for people to wonder about, so that was a good job. Looks like you should be down to the end pretty quick here. I take it the test tubes hold up well to heat and you don't have to order special ones. I want very much to have an open and visible displacer, just to add another visual component to the engine, but the only tube I have is tiny, only about half an inch o.d. I definitely need to order some test tubes of substantial size. I like very much the way you have the power cylinder and the displacer cylinder side by side, I think it makes a very good looking engine. I'm looking forward to seeing it run. :bugeye: mad jack
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First setbacks, one minor, another major. The displacer piston (the electrolyte cap.) is, I think, too short. I had to cut the glass cylinder (twice) to get it short enough. The piston should almost hit the cylinder bottom, and also almost hit the glass cylinder, at the resp. dead centers. Now it does, but the glass cylinder is a stump. Not looking good.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/1stass.jpg)
Iīm fairly certain Iīll have to make another piston and cut the other test tube. It might work as it is, but thereīs a bigger problem.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/1stass2.jpg)
That (displacer) piston rod leaks furiously. When I flick the flywheel, it goes swoosh, swoosh, with the power piston going up or down. I made sure thatīs where it leaks, with soap suds. :bang:
As you might remember, there are two Oilite bushings to guide and to seal the piston rod. They seem to guide it well, but the seal is non-existent. No wonder the piston rod was so very free to move... In the previous engine, I used the same construction, except the piston rod is 4 mm, here it is 6 mm. And in the previous engine it works perfectly. Blast. :doh:
I didnīt think that would be a problem... Now, Iīll have to push the bushings out, and then make a tighter bronze bushing (not Oilite). The piston rod I think Iīll keep, it was quite hard (sic) to make. I have a 6 mm reamer, remains to be seen if that will finish the bushing airtight, but still freely moving.
Another possibility would be a Teflon bushing. The Oilites are 10 mm dia and 10 mm long each, so there would be 20 mm to give guidance to the rod. Should be enough. Or maybe use one Oilite and replace the other with Teflon. This will need some experimenting. But it certainly wonīt even attempt to run with that kind of a leak.
So it ainīt over till the fat lady sings. And she hasnīt started yet.
:wave:
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I get the impression there is always something extra to do with these engines Olli, nearly there though. :thumbup:
Nick
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So it ainīt over till the fat lady sings. And she hasnīt started yet.
Don't worry Olli.
She's poised, and tuned up! :thumbup:
Setbacks are character building, I'm told....... :D
David D
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Well, the fat lady just started singing (but sheīs not finished yet). She sings so loud that the table shakes (the engine/flywheel is still largely unbalanced).
Some more pics.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Runner1.jpg)
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Runner3.jpg)
This shows the shorter power stroke.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Runner2.jpg)
Changes since yesterday: Pushed the Oilite bushings out, and substituted one of them with a Teflon bushing.
Changed the (=made a new) power piston connecting rod. The old one might have worked in a well-balanced engine, but it was too heavy (I told you...).
Shortened the power stroke, drilled and tapped another hole in the crank disk. The displacer volume is now so much less than intended that it cannot push the power piston all the way through the power stroke. Thereīs still a mismatch, but at least it runs, sort of.
I will make another much longer displacer piston, and cut the other test tube to size. Maybe also lengthen the displ. stroke. And make another spirit lamp. I temporarily pulled the wick out from this lamp, so I could get a bigger flame for testing (and filming). But this engine needs a lot more heat than the smaller one. And of course will consume more alco, so the itsy bitsy burner is a bit ridiculous.
The engine so far makes lots of noise, that also needs some tlc. The other one is very silent.
The flywheel(s) must be balanced. As it is, it will promptly walk off the table.
And general blinging might be of benefit..
My son will go to London next week, and he promised to get me a cigar in a one inch tube. I just need the tube, but I will smoke that cigar also :D
Always nice when a new engine behaves. :beer:
Thanks for watching, more when thereīs some significant changes.
:wave:
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She runs :bow: A great looking engine too! Ive been thinking of building a stirling engine and this thread has only helped to further convince me!
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Nice one :bow: :bow: :bow: :bow: :bow:
sweeeeeeeeeeet runner :clap: :clap: :clap:
Rob
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...
I probably wonīt be making this in a hurry, so be patient...
:wave:
Ummm... 17 days isn't hurrying? :lol:
Very nice build BTW. and she is a runner!
Great job.
Eric
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...
I probably wonīt be making this in a hurry, so be patient...
Olli! :wave:
Ummm... 17 days isn't hurrying? :lol:
Very nice build BTW. and she is a runner!
Great job.
Eric
My thoughts too Eric! :scratch:
Good luck Olli...... :wave:
I'll be patient! :thumbup:
David D
I was prepared to be very patient, if necessary. Now, I'm clinging on by my fingertips..... (http://serve.mysmiley.net/sign/sign0182.gif) (http://www.mysmiley.net)
Blummin well done Olli! :clap: :clap: :thumbup:
David D
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Well done Olli - it's brilliant! :clap:
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17 days... from stock to runner... very very nice. I am impressed. :thumbup:
Eric
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:clap: :clap: Wow Olli - you pulled this one off quickly! VERY nice :bow: :bow:
Sure beats the heck out of the fat ladies I've heard singing!
:beer: Arnold
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Well, thank you all for your comments, I didnīt think it would go this quick myself. Iīve done a few engines, and usually (=every time except this one) they have given more than enough labour pains. BUT - itīs not "finished" yet, although it runs (or at least limps). It sorely needs another longer displacer piston + tube. As it it, it wonīt run very long, some 15 minutes, and then the displacer cylinder gets too warm, and the music stops. It gets too warm exactly because it is too near the heat source. The glass tube extends now some 30 mm from the ali top, the original idea was something like 70 mm (=over twice as much!). I expect with that modification it will run "forever". And have far more power and speed.
Also I should point out that Iīm retired, so I have more time for the shop than anyone with a daily work. And with the weather mostly rainy, even a naturally lazy guy gets some things done.
Proof of which is the new lamp I put together. Rainy day, once again.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Lamp1.jpg)
The thing started as a tea light (candle), itīs made of tinplate (iron, basically), and it has a lid, with a glass window. I soft soldered a curved 6 mm tubing to it, made a small cap for the tube (to keep the spirit from evaporating, should there be any left from running). And pulled the wick into the tube. This has a far bigger flame than the other, with a 4 mm tubing for the wick. 4 mm outside = 3 mm inside = 7 mm2. 6 mm out = 5 mm in = 19.6 mm2. Not quite, but almost three times. With this lamp, the small engine really spins!
The lamp being of iron is handy in that you can fix a magnet to the base board (a round neodymium just needs a drilled hole), and it will keep the lamp from moving with the engine vibration. Thatīs why the base in the small lamp is a round steel stamping. Although I admit that all-brass lamps look nicer... :)
Thereīs more to come, but not tomorrow!
:wave:
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Fat lady doing a duet.
:wave:
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Blummin well done Olli! :clap: :clap: :clap:
Love the slower revs of the big 'un..... :thumbup:
David D
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Blummin well done Olli! :clap: :clap: :clap:
Love the slower revs of the big 'un..... :thumbup:
:clap: :clap: I agree fully with David Olli
:beer:, Arnold
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Well Oli, it looks like you've got it running, and done a very nice job in getting it so. I expect your experience with parts fulfilling your original expectations will make it run better and with more power, and make it a matter of full satisfaction. For the moment, they run very well, and certainly show your fine labor in bringing them about. I really like the glass for the displacer cylinder, and the brass/aluminum combination for looks. Good job all the way 'round :beer: :jaw: mad jack
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Well, Iīve been fiddling around with the engine, done some slight changes, and come to the conclusion that itīs "good enough". I first made another crank disk, with even less throw, itīs now something like 13.5 mm. And cut some half moons away for balancing. The con rod is still a bit too heavy, have to drill holes in it. And round it closer to the M3 head.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Newdisk1.jpg)
Then I made a little bit longer "core" for the power piston, so that the Teflon mantle comes closer to the cylinder top. When I shortened the crank throw, it of course didnīt go all the way to the top any more. Now it does.
Then there was the overheating. To improve cooling, I cut the fins in the displacer cylinder some 1.5 mm deeper. There was (and still is) material enough. And what do you know, it now keeps on working for as long as it gets its rum ration. Iīve run it for over an hour non-stop, no signs of heat death. It just keeps on choogling. Even with the pudgy glass cylinder. And with a very brisk pace also. At least as much revs as the small engine does. What it needs though is copious amounts of spirit (=heat) - a huge flame. The displacer gets way hotter than in the small engine, but it doesnīt seem to be any cause for worry. The O-ring obviously gets even a bit hotter, but itīs still the original, and no signs (or smells) of it burning. Also the glass cylinder is holding its own, but it has started colouring red.
(http://i866.photobucket.com/albums/ab229/cidrontmg/StirlBuild/Redtube1.jpg)
Iīve seen the same phenomenon in some photographs of German test tube Stirlings. Canīt say what is the cause.
I also changed the flywheel to the "original" ali thing. With the brass flywheel it would also run well, but slower.
And made yet another Teflon bushing for the displacer rod. That seems to be a sensitive point. I now left it a bit bigger on the outside, so that I really have to press it hard in its hole. And that seems also to tighten it around the rod better, itīs now quite air tight, and still very free to move.
Thereīs no Teflon tape in the power piston grooves any more, just the original mantle. What Iīve found is that oiling anything in the engine will not improve things. The Teflon piston should be as clean as possible. I often wipe it with a rag wet with alcohol, similarly clean the cylinder, wipe anything away from the displacer rod, etc. The Oilite bushing seems to slowly emit an oil film on it - no oil is definitely better.
So now Iīm left with a number of Stirling "spare parts", and wondering what to do with them...
One idea would be something like this - but I donīt have 4 extra test tubes... Just three. (First picture)
Another nice engine would be like this, except FAR bigger... (see the match for scale in the Second picture)
Or maybe not a Stirling at all.
Thank you all for the encouragement and interest! I just might post some more pictures for this thread when Iīve had enough of blinging the lady, and mounted it to a proper base board.
:wave:
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Well Oli, I have to say if fifteen minutes isn't long enough, then my flame sucker is a definite disaster, having eaten out four cylinders and six bronze pistons, with an average run time of a couple minutes, and needing work on it every five or six times I run it. As soon as I get the graphite piston done, along with a graphite valve, I hope it will run long enough to stop working on it, so I can use the one test tube I found in my box, which is about half an inch in diameter. I think you chose right in calling it "good enough", it certainly runs, and well, so don't spend too much time fiddling with it, you know you've got lots of other engines just waiting to escape out of your mind and hands. Good job all the way around :headbang: mad jack
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Well done Olli, both fantastic engines. What's next then? :poke: