Jeroen Jonkman's Sterling 60

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Ken I

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This is my version of the Stirling 60
Stirling60.jpg

I have made a few changes and build notes.
Jeroen has previously posted these for free use in the public domain so I presume he won’t mind me repeating it here.
I fully acknowledge that this is Jeroen Jonkman’s design “Stirling 60” dated 17th October 2012.

I redrew the entire thing as I prefer to have a full set of dimensionally usable drawings in AutoCad. This helps me get my head around the design and plan my way forward as to how I’m going to make the model.

Also if I make any changes or adjust to compensate for errors or size availability issue, I can more easily see what the effect is going to be.

Changes Made:

1) I changed the candle holder to an alcohol / meths burner as I frequently had soot build up from candles.

2) I did not solder the cylinder assembly to the main post (I felt there were quite enough parts soldered together in that assembly and thought it might prove troublesome) so I secured it with M2.5 cap screws.

3) I made the power piston from cast iron and added labyrinth sealing grooves.

4) I changed the candle mounting boss to tapped through so that the securing screw also became the height adjusting screw for the candle holder.

5) I made the displacer shaft bush from cast iron and eliminated the shoulder to support it in the displacer cylinder electing to go for a push fit (it doesn’t need to be terribly tight).

6) I used a Ø2 headed ejector pin for the crankshaft small end pin and secured it with an M2 grubscrew (as opposed to soldering)

7) I used the remains of the Ø2 pin as the displacer shaft. It’s a hardened and precision ground pin – an off the shelf item for plastic toolmaking etc.

8) I made all the conrods as soldered assemblies using tubes rather than machining the whole thing from solid.

9) I made the smaller columns and crank cross-head from 12mm A.F. Hex brass bar – for aesthetic reasons (although it makes the cross head easier to make and solder assemble.)

I have attached the various files. The *.zip file contains the MSword.docx build notes and the *.dxf files.

Here;s a video of it running :-
I "cheated" in that I did this from a "Hot Start" it takes a few seconds to warm up otherwise.
Regards, Ken
 

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Roger w

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Thanks for your post/ drawing updates.
I have had trouble starting mine as the drawings I had were incorrect and some parts missing.
Let you know how it goes.
Ps what clearance between the piston and test tube is the optimum?
Thanks Rog
 

Ken I

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Roger, No Idea - on mine it is 0.9mm clearance all round but I suspect smaller (like 0.5mm) might be better. I am also unsure as to how much "dead space" to allow at the end of the tube - it was one of the things I wanted to experiment with but never got around to it. On my drawings it is 2.9mm - but on my model its 4mm because I cut the test tube a little long and left it like that.

Since you can make the tube "short" and its held by the "O" rings you could play with it to your heart's content.

I had immense difficulties getting mine to run - it was just too tight - it has to be insanely free running - I got up from writing this to give my engine's flywheel a finger flick (cold engine) and is spins for about 2 seconds doing about 8-10 revs in that time. Is grinds to a halt uniformly without any jerkiness or indications of tight spots.

I spent a lot of time dressing and aligning things and finally I put a 75mm dia. expanding rubber mandrel (used for holding spindle sanding tubes) in my lathe and used it to drive the engines's flywheel for maybe a total of an hour at about 800 rpm to "run in" the motor. I must have done 5 to 10 minutes stints in alternating directions (oiling liberally) until suddenly it started working.

Since then it has improved with running more and more and now starts quite easily - rather remarkable as I once thought the damn thing would never run.

Remember its only a 1 candle power engine - that's not much even in mousepower.

Regards - Ken
 
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Roger w

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Roger, No Idea - on mine it is 0.9mm clearance all round but I suspect smaller (like 0.5mm) might be better. I am also unsure as to how much "dead space" to allow at the end of the tube - it was one of the things I wanted to experiment with but never got around to it. On my drawings it is 2.9mm - but on my model its 4mm because I cut the test tube a little long and left it like that.

Since you can make the tube "short" and its held by the "O" rings you could play with it to your heart's content.

I had immense difficulties getting mine to run - it was just too tight - it has to be insanely free running - I got up from writing this to give my engine's flywheel a finger flick (cold engine) and is spins for about 2 seconds doing about 8-10 revs in that time. Is grinds to a halt uniformly without any jerkiness or indications of tight spots.

I spent a lot of time dressing and aligning things and finally I put a 75mm dia. expanding rubber mandrel (used for holding spindle sanding tubes) in my lathe and used it to drive the engines's flywheel for maybe a total of an hour at about 800 rpm to "run in" the motor. I must have done 5 to 10 minutes stints in alternating directions (oiling liberally) until suddenly it started working.

Since then it has improved with running more and more and now starts quite easily - rather remarkable as I once thought the damn thing would never run.

Remember its only a 1 candle power engine - that's not much even in mousepower.

Regards - Ken
Thanks, I will have a go again tomorrow
😀
Thanks Rog
 

Roger w

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Started today after a lot of tinkering
Roger, No Idea - on mine it is 0.9mm clearance all round but I suspect smaller (like 0.5mm) might be better. I am also unsure as to how much "dead space" to allow at the end of the tube - it was one of the things I wanted to experiment with but never got around to it. On my drawings it is 2.9mm - but on my model its 4mm because I cut the test tube a little long and left it like that.

Since you can make the tube "short" and its held by the "O" rings you could play with it to your heart's content.

I had immense difficulties getting mine to run - it was just too tight - it has to be insanely free running - I got up from writing this to give my engine's flywheel a finger flick (cold engine) and is spins for about 2 seconds doing about 8-10 revs in that time. Is grinds to a halt uniformly without any jerkiness or indications of tight spots.

I spent a lot of time dressing and aligning things and finally I put a 75mm dia. expanding rubber mandrel (used for holding spindle sanding tubes) in my lathe and used it to drive the engines's flywheel for maybe a total of an hour at about 800 rpm to "run in" the motor. I must have done 5 to 10 minutes stints in alternating directions (oiling liberally) until suddenly it started working.

Since then it has improved with running more and more and now starts quite easily - rather remarkable as I once thought the damn thing would never run.

Remember its only a 1 candle power engine - that's not much even in mousepower.

Regards - Ken
Hi ken
Got running today, the main issue I can see is the piston rod bearing material.
To tight and it don't run, to slack and you get piston slap (which I have)
To get over this I super glued a 1mm pin on the underside of the piston , this has helped to get it running but only with a hotter flame , won't run on a candle?

Ant thoughts?
Thanks Rog
 

Ken I

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Ahh - I get it - I did not put a shoulder in the cylinder for the bush - I felt it was easier to go right through with a reamer and rely on the push fit of the bush. That also allowed me to make the bush a millimeter or so longer - which I felt would help.
I made the bush from cast iron and reamed the bore 2mm which gave a beautiful fit on the precision ground ejector pin that I used.
jjs.jpg

Since the displacer is a soldered assembly it has to be assembled in situ. However if you can get the bush to a light push fit you can assemble it and the conrod and push it into place after completeing the soldering and pin fitting operations to the displacer conrod.
Obviously you must have the fit such that you can assemble it by pulling on the conrod and pushing on the displacer without causing damage..
Another good reason to leave out the shoulder in Jeroen's original plans. This also facilitated by not having the assembly soldered to the main post or the conrod pin soldered to the crank - too many bits have to be assembled by simultaneous soldering in the original plans - leaves little room for several dissemble / reassemble debugging.

Regards - Ken
 

Roger w

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Started today after a lot of tinkering


Hi ken
Got running today, the main issue I can see is the piston rod bearing material.
To tight and it don't run, to slack and you get piston slap (which I have)
To get over this I super glued a 1mm pin on the underside of the piston , this has helped to get it running but only with a hotter flame , won't run on a candle?

Ant thoughts?
Thanks Rog
Ahh - I get it - I did not put a shoulder in the cylinder for the bush - I felt it was easier to go right through with a reamer and rely on the push fit of the bush. That also allowed me to make the bush a millimeter or so longer - which I felt would help.
I made the bush from cast iron and reamed the bore 2mm which gave a beautiful fit on the precision ground ejector pin that I used.
View attachment 115929
Since the displacer is a soldered assembly it has to be assembled in situ. However if you can get the bush to a light push fit you can assemble it and the conrod and push it into place after completeing the soldering and pin fitting operations to the displacer conrod.
Obviously you must have the fit such that you can assemble it by pulling on the conrod and pushing on the displacer without causing damage..
Another good reason to leave out the shoulder in Jeroen's original plans. This also facilitated by not having the assembly soldered to the main post or the conrod pin soldered to the crank - too many bits have to be assembled by simultaneous soldering in the original plans - leaves little room for several dissemble / reassemble debugging.

Regards - Ken
I'll order some material and change it
Thanks Rog
 

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Technical Ted

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If you don't want to have to solder the parts (I didn't) you can use Loctite 620 instead. It's high temperature and works great for this application.

Ted
 

Ken I

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Ted, thanks for the tip. Jerone's original plans also suggested that - I considered it but figured (correctly) that I would probably end up stripping it several times, I decided to go with screws for the otherwise awkward disassembly points.

Roger - when machining the CI bush make sure it comes out true - corkscrewed grain down the centre of spuncast bar tends to lead the drill astray. Its a problem I encounter all too often.

I Can't Drill Straight

If you want to be really accurate - leave the bush oversize on the OD then turn up a 2mm spiggot (light push fit) - mount the bush on it - if it runs true you have wasted your time but if it runs out then locktite it on - finish machining the OD dead true to the bore. Remove by heating to destroy the loctite and finally clean in solvent.

Regards, Ken
 
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Technical Ted

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Here's another thread that may have some info that will help you tune things up...


Ted
 

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