[40fordcoupe]

correct - some how I divided 360 by 4 and got 45 - its been a long day.

No problem, 4 out of 3 people don't understand fractions anyway. :cheers:
Cheers

[hilldude]

Try this web site its in german has a sterling like your design.I am trying to build it now http://www.manfreds-hobbypage.de/

[nick.gilling]

Hello all,

well you probably thought I'd forgotten about this, the fact of the matter was I just had no motivation to get out in the garage and start making some bits. I completed the drawings a while back and came up with (what I thought was) a sensible design, cutting out some of the fancy bits in the hope I can just make a stirling to my own design that works and utilising the materials and bearings etc I had to hand.

Over Christmas holidays I've been quite busy in the workshop and a photo is attached with my progress so far as well as a view from CAD of the revised design.

I am now realising that it was a bad decision to make the bearing pillar and displacer cylinder separate as really I could have come up with something that keeps them square to each other. Like the example posted above, that looks a good design but I try to tailor mine to what materials I have and what I think I can do.

Unfortunately carrying out this machining has once again highlighted both my impatience / lack of real experience and it has to be said rubbish machines! I know, a bad workman blames his tools and all that! I'm sure someone with a bit of nouse, or maybe even myself could set them up in order to produce better results .. but that is boring and making things that work is exciting, so I haven't bothered! Actually, I did fiddle around with the lathe for quite a while trying to set the bearings and tailstock alignment up better and also trying to erradicate the strange spiral surface finish I am getting. I thought I had sorted it but it appears not ... very annoying, I've tried everything and can't get rid of them. They are never that visible until I try to polish the workpiece with emery but then it shows up like a sore thumb. I have one last thing to try which is mounting the motor completely seperate to the lathe, I think vibration from that is inducing the marks. It's a very heath robinson drive arrangement that somebody has cobbled together but it would take a while to make a good one to replace it so I haven't bothered. If moving the motor doesn't solve the problems I'm going to invest in a new lathe in a couple of months time.

Incidentally, I'm thinking of a 9x20 or a sieg type C4, which is a new vari speed thing which has digi speed readout and a power cross feed which is pretty rare for a lathe of that size and price. The other option I have is a second hand boxford but it is the CUD which doesn't have a gearbox or power cross feed. The advantage of the boxford is that it has a back gear for slow speeds and I know they are very robust machines. The main problem with the other two lathes is that the lowest speed is about 100 rpm, which is really too fast for cast iron and screw cutting (not that I intend doing much of the latter). I'm also tempted by a mini lathe 7x12 but I think I'd regret this as they don't have taper roller bearings and think I'd probably end up wanting something bigger as I move onto larger projects. What would everyone recommend out of these?

Anyway, back to the Stirling engine.

I first made the baseplate from 1/4" mild steel plate. Basically just milled it square (I didn't bother making it exactly to the drawings I produced as the bit of plate I had required far too much material to be removed! I was quite pleased how it turned out, I thought it was pretty accurately drilled etc although I couldn't fit it in milling vice so just marked out by hand then drilled and tapped. Only problem here was that I snapped an 8ba tap, that was scary but I managed to get it out without ruining the job.

I then made the displacer cylinder pillar. This went ok, was a pretty straight forward component though. The only mistake I really made was making the location diameter slightly smaller than I would have liked. This was my impatience showing through again, I check things think there's loads still to take off and end up taking too much off. It seems to tighten down ok though and a bit of clearance here will probably help when I mess something else up later!

I then moved onto the power cylinder. I thought this had gone extremely well. I made it out of some chromium steel am hoping this will work ok with a cast iron piston. It was left over from a kit of parts I bought for an ic engine many moons ago and was for the very purpose of a cylinder so should be ok. I still need to lap the bore. I don't have any boring tools that small so drilled 23/64 and reamed to 3/8" but the finish isn't that good I don't think so will need lapping. I thought I was being clever by clamping it in place with the displacer cylinder pillar (same thread) and marking through the holes to get them exactly in right place, however, the drill must have run off slightly or I centre punched in wrong place which meant I had to file the holes out a little ... nightmare, but it fits now.

Then was the bearing pillar. There were quite a few firsts for me machining the components for this engine, and this was one of them. Never really machined square stock to round before. I managed to set it running true in the four jaw fairly quickly, I think it was more by good luck than good management though! I found it quite tedious machining it even thought not much metal had to come off I didn't like having to plunge into the workpiece and it seemed to take ages, then getting square into the corners and avoiding chatter. I should have taken the time to grind a decent tool for this. Anyway, I thought I'd done a decent job and there was just the hole for the crank / bearings to drill. I worked out how to do this in the milling machine to get them dead inline with each other. A couple of things I forgot about were a. the alloy bar might not be dead square, which wouldn't really matter. but b. the milling machine spindle may not be square to the table .... this does matter, and immediately after cutting the bearing location holes (i did them with a 3/8 slot drill) I could see they were wonkey! ( The last operation was to drill the 8ba clearance holes for bolting. This is where I realised I hadn't drilled and tapped the ones in the base that accurately, and how true the spiggot on the bottom needed to be and how little room I'd left myself by using 1/2" square stock! Because of the slightly out of position holes in the baseplate, I had to open the holes up slightly larger in the pillar, which meant being very close to the edge, so close infact that a couple of holes bulged minutely out of the sides.... another fault ( I should have designed it with 5/8" square alloy but only had 1/2".

Stupid milling machine ... think I might get a new one of those too ... thoughts are mini mill (new version with bigger table and travel and more powerful motor) or the Chester Champion 16v (this has a fixed column and the head tilts as opposed to the mini mill, which I would feel happier about, and it also has taper roller spindle bearings as well as larger capacity) any thoughts??

Anyway, I fitted the ball races which are quite a good fit and to my surprise a rod the same diameter as the crank pases through the bearings so I have decided to live with that and think I will drill out all holes in the baseplate to 8ba clearance size and put nuts underneath (cylinder and pillar). This will give me more scope for adjustment ... the way this is going I will need it!

Next component was the crankshaft. This was another first for me with machining as the design was to do the whole lot from the solid rather than build it up with shaft, disc and pin. This went pretty well really, the only snag was off-setting in the four jaw to machine the crankpin. It took ages and it's not spot on. I found that It was impossible to get the offset I required gripping on the already machined shaft so had to do it on the raised shoulder. It took ages to machine the pin with light cuts as it was offset and my impatience got the better of me again, it was almost there, it was slightly too tight a fit I thought so took one more cut and it was too loose! I think the pin will simpy turn in the inner races now but if anything is slightly out of line it might give some leway and if it stiffens up it should just start functioning how it was meant! I will see how it goes. The crankshaft looks good but on closer examination there are a couple of slight faults, one of the faces of the disc runs slightly out of true and there are some small chatter marks on the face near the pin. At least I can take plenty of "lessons learnt" from this project if nothing else!

Next was the flywheel which is straightforward. I did a half decent job on this except that I had it all worked out how to keep everything nice and true then forgot, and did something wrong! It has a very slight wobble but is better than my last attempt on the oscillating engine. The other thing I did was deviate from the drawings, the steel I used was a bit harder than I thought and larger diameter so it needed a lot taking off it, I couldn't be bothered so just left it slightly larger! It is not that heavy but has a decent moment of inertia as it spins over for ages in it's little ball bearings so at least that is something!

Well that's as far as I've got, I know there are a few tweaks to make if this is to work and I've got to improve on the remaining components! I wouldn't say I've lost heart, I've been busy and not done much for a couple of weeks but I have spent a lot of time searching the net to find which machines I'm going to buy! This time could have been better spent getting outside and trying to better set up the ones I already have though! I will get back in the garage this week, I need to keep going, then if it is rubbish, then I will invest in some new machinery ... then I will have no excuses haha!

Hope I haven't bored you to death with this but it feels good to get my experience out and down on paper!

Keep watching ... if this is too boring I can simply post pics up with appropriate smily if you like!!

Cheers,

Nick

ps on all of the turned components you can see the horrible spiral effect. The surface finish is good and smooth but you can see this underlying spiral, I just can't work out what's causing it!

[greybeard]

Nick - "I know, I know". (Sibyl, 1983)

My heart bleeds for you mate. Simillar situation here with work on the solar stirling held up while I rebuild the kitchen. Going well till the saw bench stopped. Had to strip the whole thing to extracate the worn out brushes (cheap Einhell unit).
Finally found UK stockists to order brushes (equally cheap).
Delivery time ? "4 weeks plus"
"I don't belieeeeeve it" (Meldrew, whenever)

Regards
John

[epineh]

Man, any post that big deserves at least a couple of replies

Good to see you back onto the engine. Funny I was just thinking the other day that a stirling would be nice for out situation to remove heat from the ceiling space of our home. Temperatures would be at least 70.00 deg C and I would guess it would spike over 80 degrees in the middle of the day. My plan was to install a fan to draw the heat out of the roof space using the heat from the roofing iron as the heat source for the stirling.

I only have about 3000 projects left to do now so I am sure it will be soon

Keep up the good work.

Russell.

[pminmo]

Interesting paper here: http://www.sunpower.com/lib/sitefile...ns/Doc0002.pdf

[greybeard]

Hi Phil. :wave:
Many thanks for posting that link. My only disapointment is that several of what I thought were my ideas were already there in it.
Nothing new under the solar collector, but at least I must be thinking along the right lines.
Regards
John

[pminmo]

Several interesting videos on utube: http://www.youtube.com/view_play_lis...1DAC37F9349BE2

[nick.gilling]

Just a quick update, I started making the displacer cylinder on a lathe at a model engineering club I go to. The wife has put a big side cabinet right down the centre of my garage leaving it unuseable!

The lathe is a large elliot, looks in a sorry state but it turns out it's much better than my own! I was able to accurately use the handwheels, take large cuts, get a good finish with a slow feed and power cross feed, and put machine the air cooling fins with a parting tool quite easily, I was dreading that part on my lathe. the job is still in there to finish off, it was easy drilling the hole, squaring the bottom out and tapping too.

This has made me want to buy a new lathe even more, just have to be careful in deciding what type to go for, my current thoughts now are, the bigger and heavier the better and a power cross feed is useful too, probably more use than a screw cutting gearbox as I will hardly ever screw cut threads.

Will put more pictures up in a couple of weeks.

Nick

[balsaman]

Keep going Nick! Your projects go like mine. I am always adjusting the next part because the last part didn't come out just right!. You only need to make the very last part right and all will be well!

It looks great in the pictures!

Eric

[nick.gilling]

That's true, I will be so pleased if it works, but if it ends up a static model, at least I'll have learnt a lot!

ps Just seen the photos of your assembly and I've got a long way to go to get anywhere near your standard!

[balsaman]

I make my share of mistakes Nick. I just don't tell anyone! Your attitude is good. With each part, you learn something, even if you learn what not to do. Those are hard lessons learned but stay with you. Keep going.

Eric

[cozmicray]

A coleman lantern glass globe makes a perfect displacer that you
can see the action

check out

http://www.jonbondy.com/ColemanThree.htm

there are other designs there
set them on your wood stove and push some air around!!!

[40fordcoupe]

A coleman lantern glass globe makes a perfect displacer that you
can see the action

Good idea!, what are you using for gasket material on the ends of the globe?
Thanks

[nick.gilling]

Hi all,

As you know, I have been working on my hot air engine very sporadically since the new year, well, before that if you include the design stage. I have just finished the last parts and assembled the engine. Although there are a few mistakes, the engine has gone together and seems to turn over quite nicely. The parts (I think!) were all quite a good fit and I am quite proud of my achievement as it involved lots of new techniques for me.

However, tonight I am quite disappointed as I tried to run the engine for the first time ... not only will it not run with a tea light candle (as I designed it for), but it won't even run with a butane pen torch on the hot cap with it glowing red!

I think I know the problems with it but would be interested to hear anybody else's views also! I think there are a few things:

1. The ratio of swept volumes between the displacer and power piston isn't large enough, so not a large enough volume of air is being heated and displaced. I designed it as 1:1 i.e. power and displacer pistons are about the same diameter, but with hindsight that was silly, I think that would require a massive temperature differential to get it to run, especially on this small scale.

2. The cooling on the cold end of the displacer cylinder is not good enough.

3. There is too much dead space in the tubing between the displacer cylinder and power cylinder, I've not worked this out but now I think about it, it's probably quite large compared with the actual cylinder volumes which can't be good. At the time I remember thinking I didn't want to drill the tubing too small as I thought it might choke the engine somewhat.

4. Friction - I think it's ok, it's got ball bearings for mains and big ends and seems to turn over quite well, however, I have nothing to compare against. It spins over for 4 - 5 secs with the tube disconnected between cylinders.

Does anyone have any thoughts on the above?!

My first thought is to try making a small bore copper tube as originally intended to connect cylinders and reduce dead space, don't think this will solve it though.

Then I was thinking of a larger displacer cylinder, piston, hot cap etc. bigger diameter giving a greater volume of air to heat and displace. I think at the time I designed it to suit the only stainless steel I had for the hot cap ... silly decision!

Either that or just put it down to experience and design and build another one! I changed my lathe for a much better one (Harrison L5 9"x24" with screw cutting gearbox and power cross feed) and sold my milling machine about half way through this project. I am now on the look out for a decent vertical miller so it would be nice to start something from scratch on this far superior equipment.

Maybe next time I should use a recognised design, however, I am semi confindent that I could design one of these and get it to work as it did have some small glimmer of life, it nearly picked up when the hot cap was glowing cherry red, but obviously this is a long way from what I envisaged originally!

How people sucessfully get the LTD Stirling Engines to work is now beyond me ... hats off to you guys!

Nick

[KTD1]

Hi Nick,

Welcome to the addiction! I had to set mine down for a while to do some “paying work”. I have managed to build a couple of fairly low temp engines. In response to your questions I can only say yes to all of them. Everything you have mentioned is affecting the engine. Mine run on a tea light as well. They are extremely sensitive to friction. There is only so much energy in a candle and the efficiency of the engine must be high enough to overcome the friction. For bearings I used leftover pilot bearings from router bits. My cylinders are made from borosilicate glass and the piston is made from graphite. The displacer is made from balsa wood. The engine must be also as tightly sealed as possible. Any escaping gas is thrown to the wind instead of pushing upon the piston. Dead-space is another efficiency loss as you are just using energy compressing gas that cannot be harnessed. As near as I can estimate, the ratio between swept and power piston on mine is 23.5 to 1

Hope this helps.

[nick.gilling]

Hi KDT1,

Firstly, your engines are magnificent! I can only dream of 1 day being able to produce such a piece of work!

I am determined to either get this one running or start from scratch as I have learnt some useful lessons. I like the look of mine but I have now realised it's not the best way to make it. I could have designed it so that datums were tied up and inherent in the design. Having said that, although there are some mistakes, it does spin pretty freely and I think if I make an improvement on the ratio of volumes and use a meths burner it should just about run!

Thanks again for the useful information.

Nick

[nick.gilling]

Quick update on this engine. I bored out the displacer cylinder to 9/16" and made a new hot cap and displacer piston 1/2" diameter. This now gives a ratio of swept volumes of 1.78:1 instead of 1:1 (it was never going to work with 1:1!)

The engine nearly ran with the small butane torche, however, if I also put an ice cube on the cold end the engine did run. Only at a couple of hundred rpm though.

So I think the main problems now are lack of cooling on the cold end and heat transfer between the hot cap and the cold end.

Fins are far too small, I think water cooling would be the way to go but since the displacer cylinder is aluminium it would not be easy to make a water jacket. I always mess things like that up, however, maybe I could make one up from brass sheet and glue it on with some sort of epoxy resin?

I should make a new hot cap with a flange and some insulating material between it and the displacer cylinder (cold end).

Once the ice cube has gone, the temperature difference between the cold end diminishes too much and the engine quickly comes to a stop. Not sure how long it would run with cold water surrounding the displacer cylinder, maybe 5-10 mins. I might try to make this jacket and a spirt burner and at least I can do short demonstrations then. Now that I have made the larger displacer though, the engine looks a bit out of proportion as I also took the opportunity to make it 1/2" longer.

Will post up pics and video soon.

Nick

[Mac T. Knife]

First off, I am just getting into digging around stirling engines,and I plan on building a LTD engine.

At the beginning of this thread, You planned on using aluminum for the displacer piston,,, Are you still using this? Since you are moving air back and forth from cold to hot, I would think you would want a piston made of a material that doesn't conduct heat as well. One website I read mentioned making the wall thickness of the displacer cylinder thinner where it meats up with the cold side,,,,, reducing the heat path, similar to a small gauge wire conducts less current than a larger gauge wire.

[nick.gilling]

Hi all,

Another update on my first stirling engine. I've now made a burner and a wooden base. You will be able to see that woodwork is not one of my strong points but it is OK. Also made a burner, I was quite pleased with the way that turned out, however, it could do with having a larger capacity. It runs out too quickly, I realised this as I was making it! Also, I should have offset the hole for the wick as I've found it prefers the heat to be pretty much at the end of the hot cap when running, which means the burner is right at the edge of the wood and doesn't look right! This is also because I extended the length of the hot cap as stated in previous post, this means the hot cap is now too long relative to the engine base!

I also started on a sheet brass water jacket which I think may allow the engine to work by covering the displacer cylinder in cold water. However, I'm in two minds whether to put it on, I would have to glue it somehow onto the aluminium, then I'd need to make some bits that slot down from the top and glue them in place also, sounds messy! I was thinking I could make a square aluminium plug for the top with a slot in it to make it look prettier. What are peoples thoughts on this? I could just leave it air-cooled as a static model and put this one down to experience, but on the other hand it would be nice if I could at least demonstrate it working for a few minutes!

Please see pictures and videos below,

Nick

ps. Mac T. Knife, yes I used aluminium bored out to a thin wall, as you said, you need it thin so it conducts the least heat possible. It also has to withstand a hight temperature though for this engine, for a LTD it doesn't. I also took the opportunity to make it longer which will reduce heat transfer.