Rotary Engine Build

[vederstein]

Well,

I got started on the rotary engine:

http://www.homemodelenginemachinist.com/f12/rotary-engine-design-19381/

I used my CNC'd mini-mill to do the connecting rods. But first I had to make a fixture out of some scrap to hold them. After the profile was made. I drilled out and reamed the rods.

In the last picture, the rod on the right is a main rod.

 

[vederstein]

For my limited skills, the block isn't a very easy part to make.

1. Turned down the barstock and bored out the middle.
2, Flipped the piece in the lathe to turn a boss for my rotary table chuck to grab onto. The part is larger than the 3" rotary table/chuck I have.
3. Chuck the part onto the mill and rotary table.
4. Mill/Drill the details of the five cylinder mounts.
5. Put the part back into the lathe and face off the mounting boss. There's some marks from this operation that I'll put the part back into the lathe and take a skim cut to clean it up.

 

[agmachado]

Hi,

Very cool your project!

I will watch the next steps...

Cheers,

Alexandre

 

[vederstein]

Well, a crankshaft on an rotary engine is kind of a misnomer, but here it goes...

The first step is to face of a piece of leaded 1-1/2" barstock.

 

[vederstein]

Then the idea was to turn down to .501 diameter to match the cylinder block. But after a trial fit, I realized my fit in the block well, sucked.:wall:

The block bore, which I hand reamed, was crooked. So I chucked up and indicated the block back in the lathe. I took some cleaning cuts and re-bored the block back to "squarish".

This explains why my crankshaft has a different diameter than the drawings I've submitted...

 

[vederstein]

Then I continued with the stepped diameter.

BTW: The shaft diameter was to be a .500 slip fit, but I screwed up the bore in the block. So, after cleaning up the messy block bore and turning the crank to fit, I'm quite please with the slip fit I've created. The modification was that the shaft diameter on the bore needed to be changed to fit (approximately from .500 to approximately .553 diameter).

Anyways, the next step was to thread the shaft. Now, I consider myself an advanced novice machinist. Not quite intermediate, but good enough to make some interesting scrap if you know what I mean.

So I single pointed some 1/2-20 fine threads on the crankshaft. They're not perfect, but they hold. (Good enough for the toy I'm creating).

After the threading operation, I used my parting tool the create the o-rting grooves. Then I drilled/tapped the end of the shaft for the "steam" (i.e. compressed air).

 

[vederstein]

I've never been very good at parting off, so I turned the part to diameter and cut it off in the band saw. Then I turned the part's fat end to width.

 

[vederstein]

Then I indicated the crankshaft in the mill on my 3" rotary table and drilled/tapped/counterbored the crank offset (.500".)

 

[vederstein]

At this point, one may question how the hell do these parts fit together?

The follow two pictures and video should help...

(I'll show the stand components when I have them all completed.)


[ame]http://youtu.be/bfx2fEQVMWk[/ame]

 

[AussieJimG]

That's coming along nicely

Jim

 

[vcutajar]

This looks like an interesting build. I'll be following.

Vince

 

[vederstein]

The stand isn't very difficult to make. Other than the hole/thread spacing, the parts don't need to be precision, so a bit of blueing and machining to the scribed lines is sufficient.

 

[vederstein]

Back to the CNC'd mini-mill.

The program was much more difficult (I program by hand and do not use CAM software) but the cylinder head is made. The method of manufacture is very similar to the connecting rods, but the larger size of the part required a much longer machining time. It takes about 2-1/2 hours for each part. My feeds and speeds are quite slow because I'm paranoid.

After the milling, the cross port is drilled and tapped for a plug.

Then make four more of these!!!!

In the final picture, you can see the engine starting to take shape.

 

[vederstein]

The cylinder is pretty simple. Instead of boring a piece of solid barstock, I took the simpler route of purchasing tubing to the correct ID and OD. Extruded aluminum tubing is pretty well controlled dimensionally and I felt safe using this material.

The steps are as follows:

1. Face off.
2. Use a piece of emery cloth to clean up the raw extruded surface.
3. Use a parting tool to turn in the o-ring groove that seals the cylinder to the cylinder head.
4. Part off to length.
5. Drill in the exhaust hole. (I forgot to get a picture of this step).

 

[vederstein]

The pistons are created from solid roundstock. A super-perfect slip fit with the cylinders is desirable, but not wholly required. The engine is designed to use o-rings for piston rings.

You may not have ever realized this, but typically a 10% o-ring compression is what's used for dynamic o-ring sealing. That's why a 1/8" thick o-ring isn't an 1/8" thick. The depth of the seal gland. Look at the following chart:

Seal Nominal Actual Gland Percent
Series Thickness Thickness Depth compression
000 1/16" .070" .063 90%
100 3/32" .103" .093 90%
200 1/8" .139" .125 90%
300 3/16" .210" .188 94%
400 1/4" .270" .250 93%

Ok, the larger thickness seals isn't as exact, but pretty cool though.

Anyway, the steps to make the pistons (all five) are as follows:

1. Face of the material.
2. Turn the material to size.
3. Check for fit with the cylinder and fine tune if necessary.
4. Cut the oring groove with a parting tool.
5. Cut out the center (drill and mill).
6. Part off the piston.
7. Cross drill the piston for the wrist pin.

The final picture shows the piston installed on one of the connecting rods.

 

[AussieJimG]

Great job. I like your pragmatic approach. I will be following.

Jim

 

[willburrrr2003]

Wow, this is a neat looking project! Thanks for sharing with us, and I look forward to following your progress

Regards,

Will

 

[vederstein]

The timing and rotation direction is though the crankshaft on this design, so there's only one (maybe two) chances of getting the timing right without ruining the crankshaft.

The porting is 29 degrees after the top dead center. I used a protractor to position the engine block. I then transferred punched the location on the crankshaft. Then the crankshaft was drilled to the center, cross porting.

After that I assembled the engine.

 

[vederstein]

After several hours of tweaking, I got the engine to run. I realized I made a serious design error. I thought an exhaust port at bottom of the piston stroke would be enough to get rid of the working fluid.

I was wrong. I needed to add exhaust porting in the crankshaft as well. This video is only a work in progress. I need to make a new, thicker, crankshaft for sealing and performance. I also need to open up the block bore to fit the crank.

Initially the engine is started at 60 psig. I bring it up to 80 then slowly lower it to about 25 where it stalls out.

[ame]http://youtu.be/gIxpT6YazsI[/ame]

 

[vcutajar]

At least it's turning and you seem to know what needs to be done. Well done.

Vince