My first engine Stirling 60

[Darren English]

Thanks for the encouragement.

I have now made the support beams. I won't bother to post pictures of them as they are only basic.
Just 4mm dia silver steel cut with a hacksaw and sanded to length.

 

[Darren English]

I'm back! My son is now a couple of months old so I've managed to get some spare time and get back to the build.

Decided to mill the detail onto the flywheels. Sticking with the theme of this build I've changed the drawings to what I think will look best.

They still need a final deburr and not sure what surface finish to give them, maybe black chrome?

 

[Darren English]

Has anyone else on here built one of these before?

It would be interesting to see how someone else has gone about making it.

 

[Ogaryd]

Hi Darren,
I built a stirling 60 about 6 months ago. It's a little tricky to get it running on a tee light candle. I had trouble getting the displacer shaft & bushing operating smoothly. I changed the power piston to graphite. From my experience reducing friction is the trick. I'd be happy to answer any questions.
Regards Gary

 

[xander janssen]

Hi Darran and Ogaryd,

I got my stirling 60 running last weekend. Although machining was finished several weeks ago, I just would not run more than a few turns.

Finding the problem took me a lot of playing around. The first problem was the friction of the displacer rod (polished silversteel) in the reamed brass bushing. I did not use cast iron as mentioned in the plans as I did not have cast iron at the time. When I enlarged the hole in the brass, the friction was reduced a lot without loosing the air-tightness, but now the rod was able to tilt in the bushing and the displacer started to touch the side of the testtube. Now the engine ran a few turns more than before but still not continously.

Finally I replaced the brass bushing by one made from teflon. The hole, through which the displacer rod runs, was drilled with a smaller diameter and 0.5 mm out of center to avoid the displacer touching the side of the testtube. Even with the reduced diameter of the hole, the displacer rod runs virtually without friction and the out of center gives another 0.5 mm clearance to compensate for the small amount of tilting of the displacer rod. Now the eninge runs pretty fast and continously using only a small flame as is should.

cheers,

Xander

 

[Darren English]

Thanks for the tips.

I was thinking of using Nitronic 60 for the bush and 316 stainless for the displacer rod, the reason for this is I have lot's of it laying around. A few of my customers use these in combination as bearing materials but not sure about the friction levels.

Gary, graphite for the power piston is a good idea.


Xander, I hadn't considered using any type of plastics. Certainly worth considering.

One thing that I am doing is increasing the length of the displacer bearing by a couple of mm. I'm also thinking of making the displacer with Ali instead of brass to reduce the weight. Both of these are to try and stop the displacer from tilting and putting pressure on single points in the bush.

Did you both use a brass pin as a pivot for tumbler plate? I'm a bit worried that it will wear out quickly so was thinking of using bearings.

 

[Darren English]

I started on the platform pillars today. I didn't have much time so they are not finished. I need to turn them around, face-off and drill and tap M6.

 

[Darren English]

Have now ordered some small (2x6x3mm) bearings to fit in the central pillar which will support the beam rather than just using a brass pin that the plans call for.
I'm also planing to use the sides of the bearings to add support to the beam.

 

[Darren English]

I was hoping to finish the support pillars off today but my 16C collet holder cracked almost in half.... doh

 

[Darren English]

A bit of progress.

Bearings arrived, they are on the small side!

Decided to do the main cylinder. For the tuning I used our Mazak SQT lathe, it has conversational programming which is great to use and very quick.


After creating the program you can check the shape and tool paths before cutting anything

After turning and before parting off

Milling the support pillar holes

Aligning the part before milling the top detail in

And finished

I then test fitted the power cylinder and test tube

 

[110samec]

The flywheels look a bit like car wheels Are you using CNC? your progress so far looks great

 

[Darren English]

Thanks. Yes all my machines are CNC.

 

[robcas631]

May I ask where you bought the bearing from?

 

[Darren English]

Hi Rob I bought them from here


http://www.technobotsonline.com

I've been trying out a few different suppliers and these are the cheapest

 

[Darren English]

Managed to get a free hour or two so got back to the engine.

I've finished the platform pillars, they just needed facing off to length and a 3.3mm hole drilled. I tapped them M4 by hand.
I would normally do the tapping on the machine but I've had a nightmare job this week with deep hole M3 taps snapping and couldn't face the prospect of breaking any more!


In the chuck before maching.

And after

I also made the flywheel support pillars. The process is the same as for the platform pillars just a little bigger and made from brass.
I changed a few dimensions to give a bit more rigidity.

I got in some 2mm diameter silver steel for the tumbler arm bearing pins, couldn't quite believe how cheap it was .59p (about one dollar) for a 12in length.
These I just cut to length with a hacksaw and belt sanded the ends.

 

[Darren English]

Hi guys.
A little more progress.

I made the bases. In the original plans they are made from wood, I'm taking a different direction.
I'll wait until the engine is assembled to show you, this is mainly because it might look rubbish and I'll have to change it!

I've also made the displacers. I've made these from black Acetal. Nothing complex just a radius one end and threaded the other. I'm using Acetal because I had some off cuts laying around and it is lightweight.

Can't upload pictures at the moment as computer is down, bit of a pain doing it through my phone.

 

[jwcnc1911]

Great looking build! I'm a hot air fan myself. I'm looking forward to seeing this build come together.

However, with a max temp of 180°F I don't think acetal will take the internal temp. Supposedly a tealight candle has a max flame temp of 1400°F and a usable heat of about 590°F to 650°F in your application.

Just something to think about.

 

[Darren English]

I had considered the heat. The temperature of 180F relates to keeping the materials mechanical properties, it's melting point is a bit higher.
I also figure air should be circulating around the engine keeping temperatures down, I'll give it a go and see what happens.

It's a good point though.