Author Topic: Jan Ridders' Simple LTD Stirling Engine - craynerd build log  (Read 36934 times)

Offline raynerd

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Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« on: August 03, 2010, 06:58:56 PM »
I`ve not posted this until now as I`ve got 101 projects on the go and wanted to get a little closer to finishing this one before talking about it. I have been posting little blogs on my website and so I`ve basically pulled my three enteries on this build from there. I`ve been working on this for about 3 weeks now on and off. One thing I`m starting to learn is that things take time and up until now I`ve been rushing everything to get a result ... hopefully this will pay off but yet to see....these engines aren`t easy to run but really blow me away!

This is Jan Ridders Simple LTD Stirling....

--part 1 July 15th 2010 --

I made an attempt at an LTD Stirling Engine several months ago and failed quite miserably. I know these things are temperamental but after my first attempt I did have quite a few ideas for improvements...nothing new, things that people have already been doing but stuff that I ignored! So over the last few months despite having 101 other projects on the go I started collecting materials. I decided on a glass cylinder with a graphite piston for the power piston and also point bearings as shown in Jan Ridders latest LTD simple stirling plans.

Here is the lump of graphite I`ve managed to get hold of... it is a fair old lump!


And it seems to cut OK. I hacked a long block off the top and turned it down holding the vac under the tool to pull all the graphite dust away. This was just a test but I used the same process to make the displacer piston bushings.



The power piston will have a glass cylinder. I needed to know that I can cut test tubes before I got into this and this setup worked a treat. Turning the glass slowly in the lathe I eased the dremel cutter slowly into the tube. I believe you can cut it half way and snap it the rest of the way but I actually held a cloth under it and cut right through.



Here is a collection of most of the materials. The only thing missing is the 2.5mm silver steel which I forgot to include in the picture.



The container was purchased at Asda for 1 and is about 101mm OD. I rang a plastic company and for a 100mm OD clear acrylic piece of 20mm length they wanted 12 plus 10 postage!!!! I think this will do the trick nicely and it cut far more easily than the tapered Tesco spaghetti tube I used last time - the 20mm cut off length can also be seen above!  You can also see the glass cylinder.

So I`ve now made some progress with the displacer cylinder, top and bottom have been cut and the top displacer rod hole bushed with graphite. The displacer cylinder will be permanently sealed once completed unlike some designs (and my last attempt) which used screws to clamp the cylinder in place. I think I had a problem with air leakage last time so this time I`ll stick to Jans idea of a permanent seal. I`m actually going to use sealant to permanently bond the bottom section of the aluminum to the plastic displacer cylinder. I`ve cut the top aluminum so that there is a rim of the same ID of the cylinder. This allows me to lock the cylinder onto the rim and I`ll use a small bead of silicon just on the outside join to seal the two as it is held tight without any bonding. If anything does go wrong it`ll be easier to cut this small seal if I need to disassemble the displacer again.






-- Part 2 - 21st July 2010 ---

Still pushing on with this, I have now cut a new cylinder to size and with a better finish from a 16mm OD test-tube with 14mm ID. This is the graphite piston to a perfect polished fit. This is the first time working with graphite and I`m very impressed with the fit!



Wasn`t quite finished in this picture but you can see the mirror finish starting.



This is the graphite bush for the displacer rod.




Since I don`t have a boring head for the mill and didn`t want to offset the plate in the mill, I luckly had this step drill that gave me just the 16mm by 3mm shoulder I needed just to sit the glass piston cylinder inside.




I then turned up two supports...



And here is the insert for the graphite power piston.




And what I have so far....



------ Part 3 - 3rd Aug 2010 ---

A little update here as I feel I am coming to the final straight!

Here is a picture of the parts so far but not including the glass cylinder and graphite piston - they are safe away from potential smashes! I`ve now cut the main parts for the crank shaft assembly - the displacer and piston rods, various size parts to the crank axis and of course the four webs.


I`ve also turned the tiny graphite bushes that sit between the webs and allow smooth movement of the rods.


I have now made a small error as at the same time I`ve not soldered the other axis to give the 90deg shift. I DID thread them onto the axis to keep them aligned whilest silver soldering these bits and my intention was to solder the axis for the 90 deg shift in my next "shop time". Of course when I solder the next bits, it`ll loosen the current soldered parts!! I am strongly considering gluing the other parts that make up the crank assembly. Especially with it being a stirling engine, there are few excessive forces or temperatures to worry about.



--------------------

I`ll keep updated from here, any advice appreciated. I really hope this runs!!

Offline sbwhart

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #1 on: August 04, 2010, 08:53:33 AM »
That looks nice Chris:- slowly does it is the answer.

Stew
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Offline Bernd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #2 on: August 04, 2010, 11:22:32 AM »
Nice Chris. Hope it runs for you the first time around.  :thumbup:

Now to that 101 "craynerd" peojects list. I got you beat with 202 "Bernd" projects.  :lol:  :lol:  :lol:  :lol:

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Offline Stilldrillin

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #3 on: August 04, 2010, 12:41:57 PM »
Wow Chris!  :bugeye:

Those parts are nicely made!  :clap:

Purposeful is the word, I think...... 

Good luck with future progress...... That will be a runner, no problem!  :thumbup:

David D
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Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #4 on: August 04, 2010, 04:40:10 PM »
Cheers guys, fingers crossed its a runner!  :med: :med:

I actually dropped one of these little crank assemblies last night and chipped the graphite bush so I`ve just come back from the workshop after repairing that. At one time I would have just run with the chipped one but ohh no, this is the new patient me... a new rebuild and better fitting than before  :lol:

Chris

Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #5 on: August 04, 2010, 04:43:12 PM »
Can anyone recommend a super glue that may be suitable for holding the rest of the crank assembly? - steel in brass.
Chris

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #6 on: August 04, 2010, 06:57:45 PM »
Very nice Chris  :clap: :clap: :clap: :bow: :bow: :bow:

Rob  :thumbup:

Offline mklotz

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #7 on: August 04, 2010, 07:25:56 PM »
Can anyone recommend a super glue that may be suitable for holding the rest of the crank assembly? - steel in brass.



A very handy weapon in the model engineering arsenal is Loctite 420 - a wicking superglue.  Over on HMEM I posted about a test I did on this stuff...

http://www.homemodelenginemachinist.com/index.php?topic=9099.msg98378#msg98378

Caveat:  I've never tried it on graphite.
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Offline NickG

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #8 on: August 05, 2010, 02:39:38 AM »
Nearly missed this Chris,

excellent work!  :bow:

Nick
Location: County Durham (North East England)

Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #9 on: August 05, 2010, 01:00:16 PM »
First of all, thanks for the replies! Kvom - interesting stuff regarding the loctite. A quick google didn`t bring up any obvious suppliers of loctite 420. I have heard that 601 is a good one and 603. It is certainly something I will be ordering soon.

An update ---

I`m off work for 6 weeks at present and so I`m getting more done than I ever have! - I`m having a great time between the workshop and looking after my little one.

I was lying in bed last night thinking about gluing the rest of the crank shaft and then I thought again, should I really not be following the plans! I`d also ignorantly cut the crank shaft into all the right sized little bits to soft solder into position. It was only when I chose to read the text that comes with the plans does it explain to insert that as one long piece, soft solder and cut the small sections out. Of course, despite having to remake the crank axis, this method allows perfect alignment and the only thing I had to do was set the cranks 90deg apart. I thought about a fancy jig and then decided that I could do this using a couple of pin vices.

My soft soldering leaves a lot to be desired. My flame seems too fierce and I end up with a huge blob of solder around the part. However, some time, effort and a lot of sanding got rid of the most of it.

Here is everything assembled so far. Perhaps I`ll have some time for the displacer tonight!



After going on about the displacer and how pleased I was with the graphite, I`m now not sure! It seems to move freely and when I blow it, the pressure builds up and the piston shoots out. However, the fall through test doesn`t work very well, it still falls through with a finger sealing the top... humm would you go with this piston or try and change it?  The piston will be something that could be changed once all is assembled. I`m tempted to run with it....
« Last Edit: August 05, 2010, 01:09:03 PM by craynerd »

Offline sbwhart

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #10 on: August 05, 2010, 01:55:18 PM »
These have a good choice of loctite they don't seem to stock the one your after though.

http://www.bearingshopuk.co.uk/loctite-173-c.asp

Stew
A little bit of clearance never got in the road
 :wave:

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Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #11 on: August 05, 2010, 02:06:15 PM »
Stew - Yea thanks, they do. I found those as well last night but your right, I couldn`t find that one.

Does anyone have any thoughts on the graphite power piston? As I`ve said, if you blow in the end of the cylinder if shoots out so it clearly holding a good seal but if you put your hand over the top of the cylinder, it falls down the cylinder which it shouldn`t. For saying that the brass piston insert makes it quite heavy!

Chris

Offline Stilldrillin

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #12 on: August 05, 2010, 02:16:31 PM »
Stew - Yea thanks, they do. I found those as well last night but your right, I couldn`t find that one.

Does anyone have any thoughts on the graphite power piston? As I`ve said, if you blow in the end of the cylinder if shoots out so it clearly holding a good seal but if you put your hand over the top of the cylinder, it falls down the cylinder which it shouldn`t. For saying that the brass piston insert makes it quite heavy!

Chris

Carry on Chris!

You can always change it later, if necessary......  :thumbup:

David D
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Offline Dean W

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #13 on: August 05, 2010, 09:58:03 PM »
Wow.  I miss one day and miss a whole build!  It's looking good, Chris.

I see the yoke for the piston is held in by a single screw through the bottom of the piston.  Could that be leaking
air?  It doesn't take much pressure to blow a piston out of a cylinder, but it has to be a pretty good fit to keep it
from falling through by gravity. 
If the bottom of the hole for the piston yoke isn't truly flat, it may be letting air past the fastening screw.

Just a question, not a criticism.  The base looks pretty thick.  Is it that thick in the plans for this engine?

Thanks for all the good pictures!

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Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #14 on: August 06, 2010, 02:25:34 AM »
Thanks for the questions and ideas. Sadly no pictures yet but I made the displacer cylinder, axis and connecting head last night.

Dean, good observations. You are correct about the screw holding the piston yolk in place, I have also thought that and my intention was to put a small dobb of sealant on the last few threads when I was happy with it. The plans call for the graphite to be threaded but I really struggled doing that! I guess I can`t call if I`m happy with it until I seal it up! My other thought, that Kwackers pointed out when he visted recently was that I`ve used the top part of a testube. When I cut the testtube, the finish isn`t very good so my thought was that if I use the top, I`ve only one cut to make and the top has a nice polished, liped edge. We both wondered however that if they do pull the lip of the testtube out at the top when blowing the glass, maybe the top of the testtube is not uniform or at least less uniform than if I took a middle piece from a testtube ?? - just a thought. Maybe I will attempt another piston before fitting it all together, at least there is more likelyhood it will work and it will save disappointment.

Also, regarding the base again you are correct. I need to chuck this bottom plate up and skim the bottom to 1mm thickness but not all over. I`ll leave it the same thickness at the edges, just from where the plastic cylinder rim fits I`ll bring it down to size. Sadly the Boxford is in bits at present and it won`t fit on my other lathes. My inverter should arrive in the next few days and I`ll want to immediately test that anyway so I will have to rebuild the sadlle and install the new 3 phase motor and at that point I`ll be able to do these little bits.


Thanks for looking, it is really helpful hearing others views.

Offline NickG

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #15 on: August 09, 2010, 06:15:38 AM »
Chris,

The top displacer cover on yours looks thick too - is that to drawing? I'm not quite sure how this will affect it's operation - it may retain more heat than a thin cover would, will the heat transfer as well though the thick base as it would a thin one? or if your top plate is thick, will you need the base to be thick too? I don't know the answers to these questions but what I'm trying to say is, I'd leave the base as it is until you've tried running it, as it could affect something.

I'd also try your existing power piston after sealing it up. If that doesn't work, try a new power piston first before altering the base - much easier to make than a new base!

nearly there  :thumbup:

Nick
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Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #16 on: August 09, 2010, 10:27:21 AM »
Hi Nick, just read your message. I`m trying to stick to the plans as much as possible as I believe these are tricky to run as they are so I want to work as near as possible to a known method and dimensions. The plans call for a 1mm thick base and the top I think 5mm, although my base is 6mm, I`ve now thinned it down in the centre to just shy of 1mm so the clear perspex displacer now sits on a small shoulder and the bottom disk is then recessed to 1mm thin base. I`m guessing the thicker edges could actually effect it so I may remove them if I have a problem.

I`m sure someone will correct me but my understanding is that this engines, LTD - low temp differential, work due to the difference in temperature between the top and bottom plate. In theory, the base size shouldn`t matter but of course if it is thicker it`ll take longer to heat up, especially if I`m hoping for it run of a low temperature source - like the palm of my hand  :lol: .. I wish!  A thinner base will heat up quicker and having a thicker top plate would mean it will heat up slower and therefore maintaining a great temperature difference for a longer period and greater running time. I`m guessing putting grooves in the top plate would give a greater area for heat loss and would make the engine perform better.

I am going to run with this graphite piston. I`ve thinned the top plate last night and also made the holder for the flywheel. Pictures to come later...


Chris

Offline mklotz

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #17 on: August 09, 2010, 11:24:57 AM »
Chris,

You may know this already but be aware that you can run your engine from a 'cold source' just as easily as with a heat source.

At exhibitions I baffle the onlookers by setting my LTD on a cold pack (or saucer of ice cubes) and letting it run off the heat available from the air or sunshine hitting the top plate when out of doors.  After the spectators have seen this I plop the engine onto a cup of coffee and it begins to run in the opposite direction.  Spectators generally know nothing of physics so they're astounded.

Incidentally, take the engine to your local bar/pub and do what I described above.  The trick is usually worth a free pint or two.  :D
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Offline GordTopps

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #18 on: August 09, 2010, 12:49:01 PM »
Good tip!  :D :)

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Offline kwackers

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #19 on: August 09, 2010, 01:26:22 PM »
I use ice lollies too.

People just don't get it - the idea an engine can run off 'cold' causes some of them great difficulty. They simply don't consider room temperature to be 'hot'.
In real terms though 273 deg K is almost the same as 300 deg K...

Offline mklotz

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #20 on: August 09, 2010, 01:44:45 PM »
I had one lady spectator who introduced herself to me and offered to shake hands.  I noticed that she had nice warm hands so, playing the evil genius, I set about convincing her that the engine ran on the psychic energy that humans emitted.  She looked sceptical so I told her to put her fingers on the (upper) 'hot' plate and, if the engine speed increased, it would prove that she had a good 'aura'.

She did, the engine sped up, and her eyes dilated and her mouth dropped open.  Last I saw her she was running off to tell her girlfriends all about 'psychic' engines.

My wife, standing in the background and watching all this, read me the riot act for falsely raising the hopes of the clueless but she had a hard time being serious about it for all the giggling she was doing.
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Offline Stilldrillin

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #21 on: August 09, 2010, 02:33:01 PM »
Recent show. Warm handed Spectator........




I wondered if I'd get the engine back! He wandered off with it, to show all his pals......   

David D
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Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #22 on: August 09, 2010, 02:35:27 PM »
Hi guys, thanks for your replies. Yes, Kvom, I did know they could run on a cold source but only because I`ve seen them doing so on youtube and it makes sense but I wouldn`t have considered it. I guess any temperature difference between the plates will cause it to run.

OK, here are some pictures for you. I`m pretty sure that this is all the parts are now complete and I`ll spend tonight polishing them up and then finally sealing the displacer if I have time.

Here is the displacer being cut from foam board. It actually cut very nicely on the lathe with a sharp tool, much better and more accurate than using a craft knife.


This is the holder for the displacer being formed





I next needed to make a similar holder for the flywheel. The plans for the flywheel to be glued to the holder but I wanted to be able to change it from something more aesthetically pleasing, I`m not keen on two CDs stuck together..but again I want to stick to the plans until it runs!


To make the flywheel changeable, I wanted to drill 4 holes so that I could attach it with small screws. So onto the milling machine and mounting my new Boxford spindle nose attachment so I can use the Boxford chuck. Only ever cutting gears, believe it or not, I`ve never using it this way around so have only just run into this potential disaster!! It doesn`t fit!!!!! I need a solution for future!


Luckily with about 2mm clearance I could just centre spot the hole locations but it certainly wasn`t ideal.




Two CDs were glued together and attached to the holder


And now all the pieces in the box ready for polishing and assembly!


OK, I couldn`t resist a quick mock up..notice this was a temporary single disk on the flywheel, it seems to run very very smooth but then the power piston wasn`t in. It did give me an idea of what it would look like.


Hopefully further updates shortly! I will need to leave it at least 18 hours for the sealant to dry and of course that is if I get onto it tonight.
Thanks for the comments and interest so far.
Chris





Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #23 on: August 09, 2010, 02:37:17 PM »
Oh yea, forgot to mention, I cut a middle section out of another testtube and using the same piston with no modifications it seems excellent!! Much better and doesn`t fall through with a finger on the top! :D Thanks to Kwackers for his suggestion on that one.

Offline NickG

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #24 on: August 10, 2010, 10:48:50 AM »
Chris, you're right to try to keep to the drawings with thicknesses, I've not seen one with a thick top plate before so I thought you had made it thicker.

Am I right in thinking the bottom of your base isn't flat then? How will it collect the heat, if only the thick edges contact the heat source, or are you planning to run it on top of a cup that it will drop over?

Looking good and the new cylinder sounds promising - can't wait to see the result fingers crossed, I think you have a runner!  :thumbup:

Nice work.

Nick

Location: County Durham (North East England)