Author Topic: LTD Stirling Hard to Find Materials  (Read 8077 times)

Offline NickG

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LTD Stirling Hard to Find Materials
« on: November 16, 2010, 07:13:31 AM »
Hi all

got  :proj: I'm afraid!

Jan Ridders has just made a Tiny LTD Stirling on his website but it calls for some materials that aren't easy for me to find.

It uses a 19mm OD glass tube for the displacer cylinder and a 6.5mm OD for the power cylinder. Then graphite for the piston. He uses brass for the displacer rod guide but I was thinking of using ptfe for that?

I suppose I could make them from other materials but then the power cylinder would be more difficult to make to achieve the fit required.

Anyone have any ideas?

Nick
Location: County Durham (North East England)

Offline Bluechip

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Re: LTD Stirling Hard to Find Materials
« Reply #1 on: November 16, 2010, 08:35:14 AM »
Not sure what you want Nick, but ..

Graphite stuff.

http://www.nogginend.com/index_files/GraphiteRound.htm

Never used them, no idea whether it's cheap, reasonable, outrageous ...

Found it some weeks ago, looking for some cheap PEEK. NAHIH  :bugeye:

Dave BC
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Offline raynerd

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Re: LTD Stirling Hard to Find Materials
« Reply #2 on: November 16, 2010, 09:04:23 AM »
I was talking to (mithering to death) the chap with the LTDs at the Stiriling stand at the Midlands Show. He explained that all his clear plastic displacer cylinder materials for his stirlings are from supermarket packaging. If you have a look around you`ll easily find something glass or plastic 19mm for the displacer cylinder. How about the neck section off a glass bottle of ketchup? Walk around tesco/asda with a ruler- you`ll look like an idot but I`m sure you`ll find something!

The power cylinder is where I messed up with my LTD. I cut a section out of a test tube but it wasn`t true enough. You really need precision glass tubing...which is £££

 

Offline raynerd

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Re: LTD Stirling Hard to Find Materials
« Reply #3 on: November 16, 2010, 09:05:57 AM »
Just another thing... the chap showed me a few of his running really really nicely on graphite and glass. But as he pointed out, he had a few running very nicely on brass power cylinder with polished and anodised aluminium piston!  I`ll be going with that when I try and fix mine. I can`t afford the price of precision glass tubing with delivery.

Chris



Offline BillTodd

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Re: LTD Stirling Hard to Find Materials
« Reply #4 on: November 16, 2010, 09:35:23 AM »
Test tubes - unfortunately only available in packs of 50 for £24

http://www.rapidonline.com/Educational-Products/Science/Laboratory-Equipment/Test-tube-with-rim/123522#

Lab equipment in general from Rapid:
http://www.rapidonline.com/Educational-Products/Science/Laboratory-Equipment

Middlesex university supplies:

http://www.mutr.co.uk/ - loads of interesting stuff (not cheap)

http://www.mutr.co.uk/product_info.php?products_id=8484


Bill


« Last Edit: November 16, 2010, 11:19:09 AM by BillTodd »
Bill

Offline Stilldrillin

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Re: LTD Stirling Hard to Find Materials
« Reply #5 on: November 16, 2010, 10:45:40 AM »

Nick.
I've got several "16mm" test tubes. From this unfinished session......    http://madmodder.net/index.php?topic=2006.0

No problem to post a few......  :thumbup:

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Offline AdeV

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Re: LTD Stirling Hard to Find Materials
« Reply #6 on: November 16, 2010, 11:18:48 AM »
Nick,

I have a chunk of graphite that you're welcome to a piece of; how big is the piston supposed to be? Let me know that and I'll chop some out & send it to you.
Cheers!
Ade.
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Offline Bogstandard

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Re: LTD Stirling Hard to Find Materials
« Reply #7 on: November 16, 2010, 03:12:49 PM »
Nick,

For a start, if you are not going to run it over an open flame like Jan does, you can just use plastic tube for the main displacer cylinder, because the lightweight piston doesn't in fact touch the sides, so doesn't need to be abrasion resistant or too critical on size. The power cylinder could easily be made from very finely bored brass, or even K&S tube. In fact you can run it over a naked flame, if you do it this way (kindly sent to me by Jan for running my eggcup Stirling with a plastic displacer cylinder).



So in fact, all you really need is a bit of graphite, which Ade has already offered you.

So we should be seeing it running by the weekend.


John
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Offline NickG

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Re: LTD Stirling Hard to Find Materials
« Reply #8 on: November 16, 2010, 04:03:37 PM »
Wow,

Thanks for all the information guys.

Dave BC, I wasn't sure how much to expect it to be but it is only a very small amount required so £6 wouldn't break the bank I suppose, will have to save that place to my favourites for future.

Chris, good point, I never really thought that the displacer one isn't really as critical so I could use almost anything, or as you and John say could even be plastic. I did find a 19mm test tube on ebay here which would do the job:

http://cgi.ebay.co.uk/BOROSILICATE-GLASS-TEST-TUBE-SIDE-ARM-150MM-X-19MM-/200542242789?pt=UK_BOI_Medical_Lab_Equipment_Lab_Supplies_ET&hash=item2eb13fc7e5


I've seen one on youtube last night that has a brass cylinder here http://www.youtube.com/watch?v=dAV_nWTwWR4 and I think the original one Jan based his on had a steel piston! I guess anodised aluminium would be good to keep the weight down and provide a scratch resistant low friction surface, I still have trouble with making a bore nice and round and parallel and a perfect finish though, unless I just bought the right sized reamer.  I didn't think the glass tubing would be that expensive but you've obviously done your research Chris.

Many thanks for the offer David, but I'm not sure whether it would work with a smaller displacer, I guess it would just need a bit more heat but it would change the ratio of swept volumes and all that you see! What do you reckon John?

Thanks Ade, that would be great. Jan just sent me the plans today, wow this thing really is Tiny - the power piston is 4.5mm dia x 5mm long!!! Don't really fancy my chances having seen it but think I'll give it a go none the less!

John, what is K&S tube? What is that you have between the flame and your displacer cylinder? I see you managed with the bent crank, Jan said he had to change his to a fabricated one.

Thanks again guys for the advice and offers.

Nick









Location: County Durham (North East England)

Offline AdeV

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Re: LTD Stirling Hard to Find Materials
« Reply #9 on: November 16, 2010, 04:45:26 PM »
Yipe, that is small.... You'd be able to make about a thousand pistons out of the hunk of graphite I've got! I'll slice off a piece tomorrow - there'll be loads more than you'll need for this job, hopefully enough that you can do other engines at a later date - PM me your address and I'll get it in the post tomorrow.  :thumbup:
Cheers!
Ade.
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Offline Bogstandard

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Re: LTD Stirling Hard to Find Materials
« Reply #10 on: November 16, 2010, 06:28:21 PM »
Sorry Nick, I should have worded it differently.
The photo was sent by Jan, and it is his egg cup Stirling on there. My three do in fact have built up crankshafts, but are about to be modded because I am fitting ball races onto the crank ends rather than a needle point, which I find very difficult to adjust correctly.






The problem with these tiny engines is that the size of the hot water reservoir, even a coffee cup, very quickly goes cold. So Jan shows in the picture a stand, holding a glass shot glass being kept warm by a tealight, giving at least an hours running.

K&S tube is a seamless brass tube that you can normally buy in short lengths from model shops.

John
« Last Edit: November 16, 2010, 06:32:12 PM by bogstandard »
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Offline cidrontmg

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Re: LTD Stirling Hard to Find Materials
« Reply #11 on: November 16, 2010, 07:25:48 PM »
There“s also Bengs Modellbau (in Germany), that sells many hard-to-find things, graphite and test tubes (just one, if you want just one) among them. Several sizes at http://www.bengs-modellbau.com/material/buildingmaterials/index.php
That“s a Google-translated page... I“ve bought several times of them, they send very fast. Everything high quality.
Just noticed that the English site is only a small part of the German site, graphite can be found here
http://www.bengs-modellbau.de/material/halbzeuge/
And there“s quite a lot of other interesting stuff in the German pages.
Like craynerd said, test tubes work fine for displacer cylinders, but they“re too leaky for a power cyl. They don“t need to be true, inside or out, so they have largish tolerances. Like Bogs suggested, brass (or aluminium) would be far better.
But I guess you are already covered...  :)
 :wave: 
Olli
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Offline NickG

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Re: LTD Stirling Hard to Find Materials
« Reply #12 on: November 17, 2010, 04:08:07 AM »
Thanks Olli,

Your egg cup stirlings look great John, did Jan put water in the shot glass when running or just rely on the heat it absorbs?
Come to think of it, I have seen yours before, I remember the different flywheel designs.

Does the K&S tube have an accurate bore or would it need boring & lapping? I was looking in the metal place's catalogue that I use and looking for seamless tube but wasn't sure what the finish and roundness would be like. Then I thought I could use ground steel for the piston but the graphite Ade has kindly donated will be just the job for that now.

Thanks,

Nick
Location: County Durham (North East England)

Offline Stilldrillin

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Re: LTD Stirling Hard to Find Materials
« Reply #13 on: November 17, 2010, 04:23:34 AM »
Nick.
I've used K&S 3/8" bore tube for steam loco cyls. It measured .002" oversize, and no measurable ovality. The pistons I made fit beautifully.....

http://madmodder.net/index.php?topic=3325.0

Found some in a local Craft Shop, now.  :thumbup:

David D
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Offline Bogstandard

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Re: LTD Stirling Hard to Find Materials
« Reply #14 on: November 17, 2010, 04:41:17 AM »
Yes Nick, you fill the glass with water, and top up when necessary.

As Dave has said, K&S tubing is very acceptable and should be fine for what you want to achieve, in fact they nestle very nicely inside each other, if ever you want to make something that telescopes.

No need to worry about getting it spot on internal size, somewhere near should be fine, and make the power piston to fit.

BTW, I do like the other one you showed, that lends itself for scaling down to something a little smaller because of the block on top of the displacer cylinder rather than using tubes.


John
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Offline NickG

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Re: LTD Stirling Hard to Find Materials
« Reply #15 on: November 18, 2010, 04:31:41 PM »
Thanks John,

Yeah that one I stumbled across on youtube is quite a nice design, think mine will be a bit of a hybrid of the two.

Arv, many thanks, the graphite arrived today and there is plenty to try again when I cock it up!  :thumbup:

Nick

Location: County Durham (North East England)