Author Topic: Rocker V Stirling Engine  (Read 2202 times)

Offline tvoght

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Re: Rocker V Stirling Engine
« Reply #15 on: September 13, 2017, 09:33:17 PM »
I am following along on the build of this interesting engine, Plani. Good work so far!

--Tim

Online b.lindsey

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Re: Rocker V Stirling Engine
« Reply #16 on: September 14, 2017, 12:50:21 AM »
More nice looking parts Plani. I am anxious to see things start going together and then running of course.

Bill

Offline Plani

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Re: Rocker V Stirling Engine
« Reply #17 on: September 18, 2017, 07:57:19 PM »
Thank you Tim and Bill  :cheers:

Bill, I'm anxious too. These Stirling engines tend to have some "personality" and sometimes it's hard to get them to run. Although on this one I'm pretty confident since it's a proven design to which I made only minor changes  :). So we shall see.....

I went on with the bell crank.
Some aluminum stock was milled to thickness:


Then the 3 holes were drilled and the piece was bolted down using some allen screws to mill the outer contour:


In the same setup the relief for the web was milled:


Since the holes are symmetric and only the contour of the web is uneven the same arrangement could be used to mill the relief on the second side:


Finished part:


Plani

Online yogi

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Re: Rocker V Stirling Engine
« Reply #18 on: September 19, 2017, 11:07:49 PM »
Looking good!  :ThumbsUp: :ThumbsUp: :ThumbsUp:

Offline Plani

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Re: Rocker V Stirling Engine
« Reply #19 on: September 25, 2017, 08:17:51 PM »
Thank you Yogi :cheers:

Next up, The cylinder block:
It all started with some 50mm by 50mm EN AW 6082 aluminum stock which was surfaced first to get a proper datum:


Then the relief was milled using a disc cutter:


Next the cylinder bores were roughed out, making them 1mm undersize:


Then the contour of the backside was milled:


And after milling the outer contour, the holes for the bearing stands and the bearing of the bell crank were drilled and tapped:


First side done:


The part is then turned over and brought to its final hight:


And then most of the aluminum is cut away to form the expansion cylinder:


Going round and round a couple times to mill the spherical part of the cylinder after drilling and tapping the holes for the cooler:


And the last operation is to bore out the bores with a fine feed to get a straight and round bore with a good surface finish. Here the expansion bore is done the compression bore is still to go:


The finished part, ready to be shipped to a specialized company to have it hard coat anodized:


Plani

Online Dave Otto

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Re: Rocker V Stirling Engine
« Reply #20 on: September 26, 2017, 12:35:35 AM »
Very nice!

Dave

Offline Plani

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Re: Rocker V Stirling Engine
« Reply #21 on: October 09, 2017, 10:40:07 AM »
Thank you, Dave  :cheers:

The next substantial part of the engine is the cooler. It's made from the same bar stock as the cylinder block.

First it was faced and the outer contour was milled:


The holes for the hot cap spotted and drilled. They will be tapped later:


Some material from the bore removed:


Roughing out the contour of the cooler:


Since I didn't have a suitable t-slot cutter at hand, I made a fly cutter to machine the cooling fins:


First side done:


The part turned over and removing excess stock:


The cylindric part of the bore machined:


The spheric part of the bore was milled using a ball end mill:


And finally, the o-ring groove and the port was milled and the holes for the bolts drilled:


Finished part:


The edges of the port will be rounded, to allow for a good gas flow:


Plani

Offline cfellows

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Re: Rocker V Stirling Engine
« Reply #22 on: October 09, 2017, 06:24:09 PM »
Wow, that was some heavy machining.  The result sure turned out nice!

Chuck
So many projects, so little time...

Offline Perry

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Re: Rocker V Stirling Engine
« Reply #23 on: October 09, 2017, 07:44:27 PM »
WOW.. I'm watching this too.. That will be quite powerful stirling. Does it take long time to program your cnc to do this? Now with almost zero free time I sometimes wish for a benchtop cnc.. Keep on good work!

Offline Ian S C

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Re: Rocker V Stirling Engine
« Reply #24 on: October 10, 2017, 02:50:34 AM »
with everthing else OK, the part that I find will hold up starting is the fit of the piston in it's bore, and now days i seem to get that fairly right, I used to make the fit too close, and it took a bit of running in to get it free enough to over cme friction, then a few hours running with heat to get full power, but once up to full power there is little or no wear to the bore or piston for the life of the motor. Friction is the killer of these motors, followed by air leaks.
Ian S C

Offline Hugh Currin

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Re: Rocker V Stirling Engine
« Reply #25 on: October 10, 2017, 04:18:07 AM »
Plani:

Beautiful machining. Thanks for the build thread.

with everthing else OK, the part that I find will hold up starting is the fit of the piston in it's bore, and now days i seem to get that fairly right, I used to make the fit too close, and it took a bit of running in to get it free enough to over cme friction, then a few hours running with heat to get full power, but once up to full power there is little or no wear to the bore or piston for the life of the motor. Friction is the killer of these motors, followed by air leaks.
Ian S C

Ian:

Is it then feasible to lap the piston to the bore? I've thought this would give too much space and leakage. But from what you said....

Thanks.

Hugh

Offline Ian S C

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Re: Rocker V Stirling Engine
« Reply #26 on: October 10, 2017, 11:27:06 AM »
After lapping the cylinder, I lap the piston out of the cylinder until it just fits the cylinder, and when it will slide through the cylinder, (I usually add the weight of the con rod) under it's own weight, then all but stop when the end of the cylinder is blocked off, it then should be about right. I find the final fit is more by feel than measurement.
Ian S C

Offline Hugh Currin

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Re: Rocker V Stirling Engine
« Reply #27 on: October 10, 2017, 03:00:28 PM »
After lapping the cylinder, I lap the piston out of the cylinder until it just fits the cylinder..........

Thanks Ian.

Hugh

Offline Plani

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Re: Rocker V Stirling Engine
« Reply #28 on: October 10, 2017, 08:11:27 PM »
Thank you gentlemen for the kind comments! It's very much appreciated!  :cheers:

Perry, I have a CAM program on my shop-computer. So when I'm lucky enough to hit the right buttons, it actually doesen't take very long to make a program for the mill. In this case I imported the solid model from the CAD and made the program from there.

Ian/Hugh, the cylinders of this engine will be hard coat anodized. The aluminum oxide which is formed on the surface in this process is very hard and a little porous. These pores will be treated (by the company who does the anodizing) with ptfe in order to get a surface with very low friction. And therefore I don't want to do any more machining on these surfaces except for maybe a little bit of honing in order to get the ptfe to the surface.
The piston skirt of the expansion piston will be made from cast iron and the goal is to machine it 0.01mm smaller than the bore...we shall see..... Because as Ian pointed out, the fit of the piston should be so that the piston under its own weight doesen't go anywhere when the cylinder is blocked off, but when open it should fall right through.
And the compression piston will get a lip seal consisting of some plastic bearing material which is also supposed to have a very low coefficient of friction.
I haven't done this before, and I'm really curious to see how that will work...

Plani

Offline 10KPete

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Re: Rocker V Stirling Engine
« Reply #29 on: October 10, 2017, 09:39:09 PM »
Remember that Anodizing aluminum is an additive process in that the oxide is 'grown' on the surface of the aluminum.

Talk with your plater about time/thickness for your parts so get the proper fit after Anodizing.

Pete
Craftsman, Tinkerer, Curious Person.
Retired, finally!
SB 10K lathe, Benchmaster mill. And stuff.