Author Topic: Help request for LTD Sterling Engine (Read 6516 times)

prasad · « **on:** February 10, 2016, 05:38:27 PM »

Guys,

I am a new member, got interested in MEM after visiting Cabin Fever Expo in January. Thinking of building a LTD Sterling engine that I can place over a coffee mug. I have a few questions.

In most of the web sites I visited the piston is described as made of graphite. Is graphite a must? If yes where can I buy small pieces of graphite?

If graphite is not a must then what are the alternative materials?

I have aluminum round rods. Can I make the cylinder out of aluminum?

What should be the tolerance between cylinder and piston?

Top and bottom discs: How thick should these be? I have round discs about 0.25 inch thick. I can mill them thinner if required.

Lastly the tube. I have an 4" OD Acrylic tube. Can I use acrylic or should this be in glass?

My apologies for asking too many questions,

Regards
Prasad
Eastern PA

b.lindsey · « **Reply #1 on:** February 10, 2016, 05:59:13 PM »

Hi Prasad,
First of all, are your working from any particular plans? If not I might suggest Jerry Howell's plans for his LTD Stirling. They can also supply the necessary bearings and graphite. Graphite is preferred because of its lighter weight as well as its self-lubricating properties. The fit of the piston is critical in these engines since they generate such little power to begin with. Your .250" plates will likely be too thick. Depending on the overall size of the engine, something more like 1/16" to 1/8" would be more appropriate. Finally as for the displacer cylinder, acrylic is fine, just needs to seal well with the top and bottom plates. In that regards the acrylic will be much easier to machine than glass would be.
Hope this helps some.

Bill

Alyn Foundry · « **Reply #2 on:** February 10, 2016, 06:17:41 PM »

Hello Prasad.

The simplest method is to use a rubber diaphragm as your piston.

I made one a few years ago, I used a disc of Polystyrene for the displacer attached to a PTFE rod that came through the top bushing. I made a 3/4" hole in the top plate where I then glued down a piece of rubber glove ( Marigolds, affectionately called here in the UK ) To this was delicately attached using rubber solution a small diameter Aluminium con rod.

The thing ran quite smoothly on a hot mug of tea, however I decided to put it on our wood burning stove and it went so fast it self destructed !!

The best part is that you can then obtain your graphite and substitute the diaphragm.

Kind regards, Graham.

yogi · « **Reply #3 on:** February 10, 2016, 06:26:07 PM »

Prasad, I can recommend the book from James R. Senft, titled: An Introduction to Low Temperature Differential Stirling Engines.
This will answer all your questions on LTD stirlings. Is this your first engine you are building? If so, I would recommend to follow plans of an existing, proven design. It's quite a tall order to design and build your first engine. In case you have to do some troubleshooting to get it running, it's nice to know that at least the design is sound... Don't let that sound as a deterrent. I'm just hoping to give you the best chance of completing a successful engine.

Regards,
yogi

Hugh Currin · « **Reply #4 on:** February 10, 2016, 06:29:10 PM »

Prasad:

I believe my next build will be an LTD Stirling. I'm not confident I can design a workable engine so will start from a set of plans. After looking around some I decided to start from Jan Ridders' "Low Temperature Stirling" engine. He has two versions, I like the one with a single post. He's very generous giving out plans if you email him a request.

I'll likely modify his plans but keep the critical parts the same. I can't answer your specific questions very well as I haven't started yet. I'm sure many with extensive knowledge will chime in.

I trust you'll post a build log? It would help me.

Thanks.

Hugh

Edit: Spelling corrected, see Marv's post below. I plead typing too fast, and being linguistically challenged.

Alyn Foundry · « **Reply #5 on:** February 10, 2016, 06:41:09 PM »

It's amazing how the memory fades as you get older!!

Attached the remains.....

Displacer was made from " Scotchbrite " scouring pads.

Diaphragm hole was 1,1/8".

Displacer cylinder was from 4,1/2" Acrylic tube with Brass sheet used top and bottom.

Flywheel and hub bearing was a single disc from a redundant computer hard drive. Now missing in action !!

Kind regards, Graham.

prasad · « **Reply #6 on:** February 10, 2016, 11:57:29 PM »

Guys,

Thank you for your quick replies. As a beginner I want to go slowly. Immediately I like the idea of using a diaphragm given by Graham. I found a youtube video that showed it working and I was able to understand. That may be the quickie answer for graphite. I have to find thinner aluminum sheets next. I searched for the book from James R. Senft, titled: An Introduction to Low Temperature Differential Stirling Engines. Amazon lists it for $59.14. At this price I will take a pass. I will continue to search if there is an used book somewhere.

I am waiting for the drawing from Jan Ridders. I found he has plans for many different engines. I asked for a another plan and found it a bit too much for me as a starter. Now I am waiting for the Coffee cup engine drawings from him.

Thanks everyone,
Prasad
Eastern PA

b.lindsey · « **Reply #7 on:** February 11, 2016, 12:09:04 AM »

Prasad, just be aware that these engines can be tough to get to run at times. They require close tolerances and no binding whatsoever. If this is to be your first build, you may want to consider a more forgiving project as your first build, and work toward the LTD Stirling. These can be frustrating even for experienced builders.

Bill

prasad · « **Reply #8 on:** February 11, 2016, 01:19:50 AM »

Bill

Thanks. I have been under the impression that coffee cup type LTD Sterling is a relatively easy project to build as a beginner. From what you say it may not be. That being the case could you suggest something that I can build? Much appreciated

Thank you
Prasad

yogi · « **Reply #9 on:** February 11, 2016, 02:48:11 AM »

Parsad, I payed $13.- for my book from James Senft, $59.14 is outrageous!

I'm a firm believer in building what you are interested in, but like Bill said, LTD Stirlings are the most difficult to build. So if you are not stuck on LTD, I would recommend something a bit easier to build.

Regards,
yogi

prasad · « **Reply #10 on:** February 11, 2016, 02:51:40 AM »

Hi Yogi

That makes two of you saying the same. OK, I had wrong opinion that LTD Sterling would be easy. can you suggest any model that would be easier to build? I am lost as of this moment. I am still searching for the book. I have not found any other than Amazon.com where it is listed at $59.14. I may have to look at ebay where someone may be selling a used copy.

Thanks
Prasad

b.lindsey · « **Reply #11 on:** February 11, 2016, 02:56:59 AM »

Perhaps a bar stock mill engine or oscillator. Many start with one of Elmer's Engines. There are a few build logs on the forum now or recently.

Bill

yogi · « **Reply #12 on:** February 11, 2016, 03:05:18 AM »

I just did a quick search, and sure enough, there aren't any out there for a normal price. Wow. Keep your eye peeled on eBay, like you said. That's probably the best bet.
I'll have to look through my stuff to see what I could recommend for a beginner. Does it have to be Stirling, or could it be steam (running on air)?
I have to second Bill again. Steam engine are ideal beginners engines, and Elmer has some nice designs. Look through the forum and see what else inspires you, and go from there...

mklotz · « **Reply #13 on:** February 11, 2016, 02:57:18 PM »

I hope that you're comfortable with mathematics. If his book on LTDs is anything like his Ringbom book, which I have, it will be very heavy on mathematical theory and light on construction details. If at all possible, get a look at the book before you spend that kind of money.

I've built several LTDs as well as conventional steam/air engines and I'll emphatically echo the advice to not make your first project an LTD. Elmer's engine plans can be found at...

http://www.john-tom.com/html/ElmersEngines.html

Build a wobbler, then progress to engines with articulated valves, then the latter with reverse. Developing your skills, especially patience, takes time but you'll find the journey enjoyable.

Oh, and one more thing. Unless you're building the engine from coin silver, it's a 'Stirling' engine, not a "Sterling" engine. The principle of the Stirling engine was developed by a Scots minister named Stirling and the spelling of his name matches the spelling of the Scottish city.

Stuart · « **Reply #14 on:** February 11, 2016, 03:26:22 PM »

Prasad

Have a look here http://www.model-engine-plans.com/engineplans/index.htm

Beamer works very well

The duplex engine is more difficult

The plans are emailed and contain construction notes

Stuart

AOG · « **Reply #15 on:** February 11, 2016, 05:17:50 PM »

I would like to recommend Elmer's number 25 as a good starting place. My build log can be found here:

http://www.modelenginemaker.com/index.php/topic,3945.0/all.html

It will give you an idea of what your up against

Tony

MMan · « **Reply #16 on:** February 11, 2016, 05:25:24 PM »

Hi Prasad,

I did an Elmers 25 as my first. The written article that describes making it is worth following too. The way it is structured, each new part involves learning a new skill. Very enjoyable.

Do not give up on Stirlings for the future, just not as a first engine.

Mman.

NickG · « **Reply #17 on:** February 11, 2016, 05:48:36 PM »

Hi Prasad, most people start with an oscillating steam engine. They have few parts, simple, quick to build and forgiving in their design. That's not to say you should but I would consider it first. There are lots of designs freely available on the internet.

Bertie_Bassett · « **Reply #18 on:** February 11, 2016, 07:47:00 PM »

my first (and so far only) engine was a LTD stirling roughly built around one of jan ridders plans. mostly made out of what I had to hand and most ppl thought it wouldn't run!

although I had a few hiccups making the crank and getting a good seal on the displacer shaft it actually ran second time around and was actually easier then I thought it would be.

fcheslop · « **Reply #19 on:** February 11, 2016, 07:52:58 PM »

Hi Prasad, have another look around Jans site as he has a very good write up about designing Stirling engines may save buying the book.
My first Stirling was Moriya by Mr Senfit the drawings are on the web for free and can thoroughly recommend it as is fairly forgiving for a simple rag hand like me.
On Huib Vissors site I think there is some links to simpler Stirling builds also on the BloOOo forum there is a nice design for free
As others have said a Stirling may not be the wisest choice for a first build but you know youre own capabilities.

cheers

prasad · « **Reply #20 on:** February 13, 2016, 11:46:42 AM »

Quote from: Bertie_Bassett on February 11, 2016, 07:47:00 PM

my first (and so far only) engine was a LTD stirling roughly built around one of jan ridders plans. mostly made out of what I had to hand and most ppl thought it wouldn't run!

although I had a few hiccups making the crank and getting a good seal on the displacer shaft it actually ran second time around and was actually easier then I thought it would be.

Thanks Bertie, that is very encouraging. I viewed your photobucket video. Looks great. I am still lost on materials I need to gather before jumping to a model.

Regards
Prasad

Doc · « **Reply #21 on:** February 13, 2016, 04:19:06 PM »

With a LTD engine you need to be very mindful of fits and clearances they are a pain to get working correctly. If this is your first build I would suggest taking your time and make sure you have the fits and sizes correct. I myself did not start with a LTD I built several steam engines and a atmosphere engine (called a flame licker) before I did an LTD. Of all my engines I've built I would say the most finicky and hardest to get running was the LTD. But don't let that discourage you just as I say take your time.
Here is a video of one of mine running on some ice placed on the top plate I did that with some dry ice too but it seemed to run about the same as just plain old ice. It will run on a cup off anything hot too this vid was I was just playing around with it. I think they have sat on the self since and have not been run I made 3 of them.

<a href="https://www.youtube.com/watch?v=rBly6VJSRzQ" target="_blank">http://www.youtube.com/watch?v=rBly6VJSRzQ</a>

Bertie_Bassett · « **Reply #22 on:** February 13, 2016, 05:31:56 PM »

like I said, I used what I had to hand.

main plates were about 11mm thick, I recessed the base so it was only about 2mm thick to aid heat transfer.

the power cylinder was a glass test tube, with the piston made from an old motor brush. displacer cylinder was made from balsa wood sheet and is hollow. The rest of the bits were the gears and shafts from an old valve actuator.

oh and the displacer shaft seal was made with a small bit of black delrin, pvc should also work well there. I did a build log over on madmodder if you want any more details.

if your carefull the bearings in an old hard drive are perfect for these engines, as they have so little resistance

Doc · « **Reply #23 on:** February 13, 2016, 05:54:33 PM »

I tried to use Delrin but found it to be problematic it would work for a while then not I think the Delrin takes on moisture and then drags a little too much. I changed it out for graphite and it solved the problem.

NickG · « **Reply #24 on:** February 13, 2016, 06:30:45 PM »

Yes, graphite or PTFE for the glands would be ideal.

Zephyrin · « **Reply #25 on:** February 13, 2016, 08:02:45 PM »

If you have not played already with an engine, buy a cheap one, as easily found on eBay. You will appreciate the goal to reach as regards freedom of movement, and airtightness. It is a point hard to feel without testing it, and hard to describe in post...and building your own, that I suggest much larger than these commercial engines, would be certainly more straitforward knowing that.
Absolutely free movement and airtightness together, this is difficult to do for a first...

NickG · « **Reply #26 on:** February 14, 2016, 05:02:24 PM »

Zephyrin, good advice, I did the same - then decided there was no way I could match the CNC accuracy (might have a go now after numerous steam engines a hot air engine and 3 flame lickers). I got the vast majority of my money back re-selling on eBay.

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Author Topic: Help request for LTD Sterling Engine (Read 6516 times)

fcheslop