Compressed Air V8 Cirrus

[cfellows]

Well, I seem to be back in the engine building mode. I want to pick back up on the compressed air powered Cirrus engine, but I decided to go with a V8 version. It will have a 3/8" bore and 1/2" stroke. I'm making it relatively small because I don't want it to use a lot of air and make the compressor start up every 30 seconds.

I started some tentative machining yesterday trying to make a cross-plane crankshaft. My first attempt didn't turn out very good.

It all went together OK, but when I chucked up one end in the lathe, the runout on the other end was abyssmal, like 1/4". So, I moved on to my second choice, a crankshaft turned from solid.

Here's a picture of the raw stock. I turned a 1" diameter piece of 12L14 down to 13/16" and drilled center holes in each end.

I had to noodle on it a bit to figure out the best way to do it. I decided in the end to turn it between centers. So the first problem was to drill center holes on each end, at 90 degree intervals 1/4" off center. I needed an identical set of holes on each end, and each corresponding pair of holes have to be exactly opposite each other. Luckily, I have a nice tool makers vice that is ground square and flat on all sides, so I was able to clamp the blank in the vice, then use my height gauge to find the center and scribe lines all the way around and a second set at 90 degrees to the first. I also scribed a center line on the face of Jaw #1 on my four jaw chuck. Using the 4-jaw chuck to offset the the work by .25" I drilled the holes, loosening the work and rotating it 90 degrees between holes, lining up the radial line on the end of the blank with the scribed line on the face of the chuck jaw. I think I got them pretty true.

I'm designing this engine as I go, so work may be slow at times. Just hope I can see it through to the end. Tomorrow I start turning the connecting rod journals, saving the mains journals until last.

Chuck

 

[steamer]

I'll be watching Chuck!

Dave

 

[Don1966]

Ha! Chuck welcome back to the grinder. I quess you got tired of the honey do's. I be here watching bud.

Don

 

[vcutajar]

Will be following also.

Vince

 

[ShedBoy]

Welcome back Chuck, this sounds like a great idea.

Brock

 

[gbritnell]

Hi Chuck,
I would try milling as much of the stock away as possible. Milling is a much smoother operation than trying to plunge in with some sort of necking tool. Naturally to finish the journals it will need to be turned on a lathe but I have found the less you have to do on the lathe the better.
This should be a great project.
gbritnell

 

[cfellows]

I took George's advice and milled away the bulk of material around the soon to be connecting rod journals.

Then I went back to the lathe and turned the journals down to their finish diameter of 7/32". This was done using my 4-jaw chuck, not between centers as originally planned.

I still have to widen the gap which I will do next.

 

[stevehuckss396]

I want to pick back up on the compressed air powered Cirrus engine, but I decided to go with a V8 version.

So is this going to look like a Whittle V8 only bigger!!

 

[tvoght]

Hi Chuck,
Did you re-chuck after each journal so that the journal you were turning was just beyond the jaws?

I'll be watching your build,

--Tim

 

[cfellows]

So is this going to look like a Whittle V8 only bigger!!

Hi Steve, yes I'm using the Whittle in terms of overall look. Don't know what the bore and stroke of the Whittle is, but mine is 3/8" x 1/2". The cylinder barrels will be 5/8" x 3/4" and the overall length of the crankcase will be about 3" or a little more.

Chuck

 

[cfellows]

Hi Chuck,
Did you re-chuck after each journal so that the journal you were turning was just beyond the jaws?

I'll be watching your build,

--Tim

Yes, I rechucked the blank in my 4-jaw for each journal. I used a live center on the outboard end, loosely applied mostly just as a guide. The spindle speed was low, around 600 RPM.

 

[AussieJimG]

I watch, I learn. Thank you Chuck I am following.

Jim

 

[cfellows]

I finished up the crankshaft this afternoon. Turned out really nice. Of course, it took me all day to make it. Quite a process!

Kind of hard to tell from the photo, but this is a cross-plane crankshaft. That means that the throws are 90 degrees apart as you proceed from one end to the other.

Chuck

 

[Don1966]

That looks great Chuck, was it difficult to make? I only count 7 throws, how can that be since this is a V8? Anyway I am still following your progress.

Don

 

[cfellows]

That looks great Chuck, was it difficult to make? I only count 7 throws, how can that be since this is a V8? Anyway I am still following your progress.

Don

Thanks, Don. Actually there are 5 main bearing journals and 4 connecting rod journals. There is a main bearing journal on each end and 3 in the middle. There are 4 connecting rod journals and each will hold two connecting rods.

Chuck

 

[Ogaryd]

Hi Chuck,

That crankshaft sure looks pretty, Keep up the good work.

:bow: Gary

 

[cfellows]

Hi Chuck,

That crankshaft sure looks pretty, Keep up the good work.

:bow: Gary

Thanks, Gary. I showed the crank to my wife this morning. Usually all I get is a grunt or something like, "Oh, that's nice". This morning she said, "Wow, that's cool. Looks like a piece of jewelry".

Chuck

 

[kutzdibutz]

Hi Chuck,

Haha- another common reply would be: 'What? And that small thing took you all day??' :big:

But sure the part looks great!
I would have big respect making a crankshaft from one piece, I'd rather build the crankshaft with big diameter and thin ring ball bearings, center pieces and bolts. Mainly because I could correct small mistakes by re-doing comparably small and easy pieces, not the entire shaft. Hmm- I guess thats part of the 'growing with the experience' what challege one seeks...

... and certainly the bling-effect is much higher with your approach! :bow:

Cheers, Karsten

 

[cfellows]

Got some more done on the engine today. I started roughing out the top part of the crankcase.

Here is a picture of the block I'm using. It's magnesium and was cut from a 1" thick piece that I've had laying around for a long time. The overall dimensions of the block is 3" x 1.7" x 1" thick.

Here is the block mounted in my milling vise read to surface one of the sloping sides. I'm using a 1.25" indexable face mill to form the 45 deg angled faces.

This is the block with one of the angled faces finished. This magnesium machines really nicely. I was able to mill away .100" on each pass.

And here is the piece with both angled faces milled, along with crankshaft for size comparison.

I was careful to vacuum up all the magnesium swarf after I finished. It's not likely to catch fire since the kindling point is around 700 degrees, but didn't want to take any chances...

The next step will likely be to hog out the underneath side of the crankcase. Not entirely sure how I will do that, probably with an end mill.

Chuck

 

[cfellows]

This is iteration #2 of my crankcase, top half. The first one would probably have worked, but I missed a lot of the dimensions, by a lot, so couldn't in good conscience continue with it.

With this iteration, I've mounted the crankcase half in my dividing head. I will use the rotating motion and lower the end mill a bit at a time to achieve a semicircular, concave cutout in the metal. I think this will give me a lot more consistent result. The metal cuts really nicely so I don't think the long overhang will be a problem. I plan to go slow. Could really use a CNC mill at this point, but this will have to do.

I may shoot a video of part of the process to show how it works. This is work for tomorrow.

Chuck