Opposed Piston Engine

[jwcnc1911]

Fantastic Gail!  I'm extremely interested in these right now.  The latest HSM has an "OPOC" in it.

I will be following this, it seems like an IC engine I could get into.

[GailinNM]

For those interested there is a wealth of information on the internet on opposed piston engines.

A couple of places to start for a historical perspective are:
http://en.wikipedia.org/wiki/Napier_Deltic
http://en.wikipedia.org/wiki/Opposed-piston_engine

For a more modern view start at:
http://www.ecomotors.com/
and do a search on EcoMotors.

EcoMotors Is a 5 year old startup company starting to build a modern opposed piston engine for automotives.  Building a plant in China and has an impressive list of backers including Bill Gates.

My version is just for fun. 

Alan: I don't expect vibration to be a problem.  Hoping for low enough speed operation that it won;t be.  I did nothing during design to minimize it.  Also everything is fairly massive for such a small displacement so I expect that to soak it up as it did on the "Tiny" series.

JW: I don't get HSM anymore so was not aware of the OPOC article in it. Thanks for mentioning it.

Gail in NM

[swilliams]

This looks like alot of fun Gail, I'm following

Steve

[GailinNM]

Enough of the introduction.  Time to make some chips.  I don't have all the parts detailed out so they can be made but I have at least one solution worked out for any problems that I can think of. Besides there is nothing like making a few parts to commit you.

I started with the flywheels on this engine. Nothing new and exciting here that could cause a design change. Besides I had the material. 

I bought some 2-9/16 (2.562) diameter 12L14 bar stock ends from a screw machine shop that runs BIG screw machines.  After sawing off a couple of blanks 0.425 inch thick I faced off both sides to a finished thickness of 0.375 inch.



I already had a set of soft jaws for the mill vice to hold this size of stock as I have used the stock for several other projects. Using the CNC mill the spoke relief depth and the spokes were cut from one side.  The spokes were cut deeper than necessary so after flipping the flywheel over all that was necessary was to cut the relief to expose the spokes.  A 0.375 hole was put in the center to mount a taper lock hub in later.





And a pair of flywheels. After the hubs are mounted the outside diameter will be turned on a mandrel so they run true.  A little bit of light polishing would be in order also.



Gail in NM

[GailinNM]

OK,I know that making flywheels is not very exciting.  Notice however that even though I used CNC on these it would not take a lot more time to do these on a manual machine.

The flywheels were fairly generic.  Could be used on a lot of projects so now we really start to get committed with a part that lis fairly specific to this engine, The crankshaft.

The crankshaft has 3 throws with the center one 180 degrees out from the two outside ones.  I started off with a piece of 3/4 inchl diameter 1144 steel finished up to a length of 4.25 inches.  I chose 1144 steel, sometimes known as Stressproof, as it has very little tendency to warp when being cut.  It also machines very easily.

The ends were turned down to a finished diameter of 0.187 to fit a 3/16 X 5/16 flanged ball bearing. The center section length remaining is 1.593.



A note on the bearings used. For the Crankshaft the industry standard part number for bearing is FR156ZZ.  The F stands for flanged and the ZZ suffix means it has a shield on both sides.  For several years I have been buying my small bearings from:
http://www.avidrc.com/product/1/bearings
Most small bearings are US$1.00 each with prompt shipping at nominal cost.
Other bearings that will be used on this engine are R133ZZ (3/32 X 3/16) for the crosshead and FR2-5ZZ  (flanged 1/8 X 5/16) for the camshaft.

Gail in NM

 

[GailinNM]

With the throws being 180 degrees apart, it's time to turn the round center section into a flat center section 0.250 inch thick.

The blank was set on a wide parallel and 0.250 inch was machined off one side.



Then the blank was turned over so the just machined flat was resting on taller parallels and again 0.250 was machined off.  This will leave 0.250 in the center.



And the results looks like this.



Gail in NM

[GailinNM]

To Machine the throws (Crankpins) I made a simple fixture.  Starting with some 1-1/8 inch diameter 12L14 I turned about 5/8 of an inch down to 1 inch diameter and then parted it off to 3/4 inch long so it left a1/8 wide rim.  The part was tnen reversed and the parted off face was cleaned up.  None of these dimensions were critical except the 1 inch diameter need to be close enough to grip well in a 1 inch collet.

Over to the mill and the parts was clamped in a vice using a vertical vee block and centered under the spindle using a dial test indicator. I zeroed the dials, actually the
DRO in my case. Moving over 0.250 inch (half of the 0.500 stroke) a 3/16 holde was drilled and reamed. Switching to a 1/4 inch endmill a slot 1/4 inch wide and 3/32 deep was milled on a line through the just drilled hole and the center of the part.  I know my endmill cuts slightly narrow so I moved over just a bit on each side and cleaned up the cut until the 1/4 inch wide part of the crankshaft blank fit smoothly in the slot.

Last operations were to band saw a slot so the fixture could compress and grip the crankshaft blank and to deburr  the fixture. 

It does not make any real difference if the fixture grips on the 3/16 shaft or the 1/4 inch wide section. One will  grip and the other locate in either case.  Close is good enough.




Gail in NM

[GailinNM]

After applying marking out fluid to one side of the crankshaft center section, a rough layout of the crankshaft was scribed on the blank. The excess material around the center throw aws sawed away but the end throws left intact.





Inserting the crankshaft into t0he fixture we made, the fixture was clamped in a 1 inch collet in the lathe.  It would just a well in a 3 jaw chuck as long as the slit in the fixture is roughly between two jaws. I used a 1/16 inch parting tool to turn the crankpin to 5/32 diameter (0.1563).  There are many different ways advocated to turn the crankpins, but I have never had trouble just using a well sharpened parting tool accurately set to center height.



While squaring up the parting tool, I had set the compound over to 30 degrees. So with the same setup I cut the web on the tail stockj end of the blank.



The blank was reversed end for end in the fixture and the the other web was finished up on the inside throw. The crankpin was polished using a 400 grit abrasive cloth strip.

The excess material on the outside throws was sawed away.


the The crankshaft was installed in the fixture with the outside throws on center.  The crankpin NEAREST to the headstock and the associated web were turned the same way that the center crankpin was turned.  Then the crankshaft was reversed end for end and the last crankpin was turned.  Both of the crankpins were polished. and the finished crankshaft looks like this.



Gail in NM

[smfr]

You've been busy, Gail! Looks like good progress so far 

Simon

[Bearcar1]

Onya' Gail. I like the method you used for turning that crank. The fixture is simple and functional. Very good    I can't wait to see more.


BC1
Jim

[GailinNM]

Simon: Not really too busy.  The flywheel and crankshaft were both made several weeks ago.  I wanted to make sure of my post stroke capabilities before I published anything.  I have a few more parts made that I will post on then things will slow down as I have to make parts to be able to write anything.

Jim: I have been using a that style fixture for many years now.  It has limitations but if the crankshaft does not exceed them it works well.

Don't expect much this coming week.  Doctors are going to play games with my eyes and I won't be able to see well enough to do much in the shop or on the computer.  Also I am gaining two new grandchildren as the courts finalize their adoption by my daughter.  She has been fostering them for two years so I have been their temporary grandpa for that time. Really the only grandpa they have ever known.  Big family gathering as soon as the judge signs the order.

Gail in NM

[vcutajar]

Following quietly from the background.  Thanks for the detailed descriptions.

Vince

[NickG]

Gail, the CNC'd flywheels came out well. Is that a CNC you've built yourself? Did it do them just by moving the x and y axes? Presume so or that would have been a chuck rather than a vice if a rotary table was involved? Probably shouldn't be but I am surprised at how round things are by moving 2 axes at 90 deg to each other at coordinated speeds!

Like the fixture for the crank. I've used similar for disc type open ended cranks before, the problem being it is liable to slip but yours can't. I've recently had problems with a crank like this pinning and loctiting, the time taken to whittle the stock down and make the fixture was probably less than me messing on trying to pin, loctite and straighten it, might end up have to silver solder!

Nick

[Tennessee Whiskey]

Gail, great little fixture. Are you setting the tailstock over or is there another little neat fixture on that end also?

Whiskey

[ths]

Good on your daughter, and good on you.

Nice crankshaft demo.

Cheers, Hugh.