Jeroen Jonkman's Sterling 60

[Ken I]

This is my version of the Stirling 60

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

 

[saaq22]

thanks sumch

 

[Brian Hein]

That is very nice. The brass and wood look spectacular together

 

[Roger w]

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]

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

 

[Roger w]

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]

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]

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.

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]

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

 

[Technical Ted]

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]

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

 

[Technical Ted]

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

https://www.homemodelenginemachinist.com/threads/stirling-60.30328/
Ted

 

[almega]

I realize this is a bit old but I am taking a crack at building a variation of this engine and wanted to understand how you made the displacer body. Did you spin some brass sheet and then solder in the base?

 

[Technical Ted]

I'm not sure how the OP did his, but I've made three of these. I machined mine out of 360 brass round bar stock, making it around 0.015" thick walls. I drilled the ID and then went in with a rounded end mill to produce the internal radius. Then, machined the OD and cut off. I made a steel plug with a matching radius on it to insert inside when I turned the piece around in a collet and machined the OD radius. This plug gave it support while machining. I choked it up in the collet as much as I could to give it the most support.

Worked well on all 3 of mine.

Ted

 

[Ken I]

Almega, The base and tube were turned and soft soldered together - it hasn't come apart yet - so it doesn't seem to get hot enough to melt the solder.
The original highly polished finish has developed a darker golden patina with use.

I drilled the bore of the body and followed up with a 12mm diameter spherical mill for the inside.

After measuring very carefully, I turned a sacrificial mandrel in aluminium - and using a radius turning attachment machined that to a matching R6.0 end - I then locktited on the body - backed up the radius turning attachment 0.35mm and finished the end.
Trying to machine a 0.35mm wall will just deform without the mandrel support.
Removed by heating with a butane torch until the locktite degraded (and the fumes blew it off). A quick clean in Acetone to remove any residue.

Have a look at the drawings and build notes attached to post #1 (The MSword file build notes are in the Zip file).

Regards, Ken

Edit - Technical Ted - you posted when I was typing - so we both used the same method independently.

 

[almega]

Ted & Ken - Thanks a bunch for the responses. It seems you each used a similar solution and I will give it a try. I was going to use aluminum for my displacer since it is much lighter than brass, but I think I may have an issue trying to solder it, so that is probably out. I will give your solution(s) a try and hopefully will have success. I also have to build a radius cutting tool for the external radius. Oh well, just another project to do while I wait for the bearings and some metal to arrive. Thanks again to you both.

 

[Technical Ted]

I have a ball cutting attachment I made, but I simply used a radius tool made out of a piece of HSS. 360 brass cuts very freely. Just take it easy. Also, I used 620 Loctite and haven't had a problem with any of the 3 engines. IMO, brass looks much better than the aluminum, but beauty is in the eye of the beholder!

Ted

 

[almega]

I finally took a crack at this and made one in 12L14 and a second in 6065. Both worked out great and resulted in wall thickness of a little under 0.015". Rather than solder the end cap I will be using high temperature JB Weld, good for 1000 F degrees. Alcohol burns at about 760 so should have no issue with the adhesion. I appreciate the help and suggestions.

 

[Technical Ted]

I used high temp Loctite on my brass ones and they are holding up fine, so I'm sure the JB will work well for you.

Ted

 

[Steamchick]

I collected some aluminium cigar tubes for this... but have not made an engine... yet...

1. Does the end need to be hemispherical? - or is it just aesthetics? Does look good anyway.
2. Do you fill the displacer with wire wool or anything? A model I bought told me to do so, but didn't give any clues as to "how much" wire wool to use... Any suggestions?

Ta, K2