# A radial 3 cylinder compressed air engine ...



## MuellerNick (May 2, 2013)

Hi!

An other side-side-project (note, that the nesting level is reduced) is this little aerial 3 cylinder radial compressed air engine. While working on a side-project, I realized that I could recycle these cylinders. The other ones were more complicated, so I removed that portion of the code and cut down the machining time for one cylinder to less than 5 minutes.
Only thing missing was all the rest around the cylinders.
Many years ago, I already had built a similar engine that I liked a lot. So I already had a vision how it had to look like.
I wanted to make the case as a casting. So I have drawn one and almost wanted to start milling the pattern. But sleeping over it, I had a way better idea when I woke up. Threw the whole work away and started new.

That's how it looks like:




















Now, it is almost 3 o'clock in the morning here and I have assembled two more variants:


A different color to the left, and a bare metal one (just tumbled) in the middle.

I have more pictures for you to come, but you'll have to wait 'till Monday. I'll leave for a vintage motorcycle fair this morning.

I intend to publish the plans, but I do have to draw them first. My sketches aren't any help for anybody except me.

And here is a machining video of the case:
[ame="http://www.youtube.com/watch?v=lIjrwBpEduY"]YouTube[/ame]

Nick


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## Conibear (May 2, 2013)

Nice Very Nice Am looking forward to your plans.


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## MuellerNick (May 2, 2013)

Oh, re the "compressed air". You don't need a compressor! It already runs if you blow into the tube.
So a really green product, for the Californian market. hahaha


Nick


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## MCRIPPPer (May 4, 2013)

how do the valves (if any ) work on this engine? is there an exhaust valve? 



very nice looking engine!


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## MuellerNick (May 5, 2013)

Here are a few more pictures:


The fully machined case.



and from the back



A cylinder barrel. The fins are 0.4 mm wide, the grooves too. Maybe a bit challenging. I'll change that in the drawing to come.



The cylinder head. The left port on the left head is just a fake for the exhaust. There is only one port that makes the air in and out. And this one has a connection to the cylinder.
Machining the head was a bit odd. That part never saw a lathe, all done on the mill.



The crankshaft's web. Also completely done on the mill. A 10 mm mill for roughing, a 6 mm mill for milling the pin and the bore. After that, a thin disk mill to mill the collar on the back. The disk mill also finally cut off the web from the bar stock.



The crankshaft's shaft. Turned and then milled in the rotary axis. The circular groove, the flat and the bore do all the valve work. I'll come back to that in a later posting.



Piston (out of PA6) and the conrod. The conrod was milled from flat stock and then each layer sawn off. I used two spindles of the mill. The HF-spindle for the shape and the standard spindle for cutting off with a circular saw.



The pattern and the core box.
The pattern for the cylinder heads is quite straight forward.


Nick


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## MuellerNick (May 6, 2013)

And now for the plans 
View attachment Ansaugrohr.pdf

Inlet tube

View attachment Auspuffrohr.pdf

Exhaust tube

View attachment Gehaeuse.pdf

housing

View attachment Kolben.pdf

Piston

View attachment Kurbelwange.pdf

crankshaft web

View attachment Kurbelwelle-W.pdf

Crankshaft shaft

View attachment Kurbelwelle.pdf

Crankshaft assembly

TBC


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## MuellerNick (May 6, 2013)

View attachment Pleuel.pdf

connection rod

View attachment Spinner.pdf

Spinner

View attachment Zylinder.pdf

Cylinder

View attachment Zylinderkopf.pdf

Cylinder head.

If there's something missing, let me hear.
Don't take all dimensions too seriously (like the 10.39, 17.49 & 24.48 in the housing's plan).

Have fun!
Nick


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## cfellows (May 6, 2013)

If you'll pardon me, I assume the green part is the core box and the other, larger part is the pattern?

How did you make the pattern?

Thx...
Chuck


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## MuellerNick (May 6, 2013)

> If you'll pardon me, I assume the green part is the core box and the other, larger part is the pattern?



It is the other way round. The pattern is green and is a positive (embed in sand -> negative, pour with aluminium -> positive)
Same with the core. Just an other breed of sand.



> How did you make the pattern?


The core box now? Well, I milled it. What can I say? 
Milled it in three layers (or two?) because it is quite deep. Too deep for the 1.5 mm mill that I used therefore.
Anyhow, the pattern was milled the same way, also in several layers.
I mill one layer, glue the next one on top of it, mill that one with 1 mm overlap (and hope no glue-drops running down the cavities of the first layer).


Nick


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## MuellerNick (May 6, 2013)

Here is a short video of it running:
[ame="http://www.youtube.com/watch?v=3mOuUmQy2UI"]YouTube[/ame]

I have cleaned the lens now! hahaha


Nick


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## Chriske (May 9, 2013)

Very nice engine...!


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