Author Topic: Opposed Piston Engine  (Read 62305 times)

Offline Bearcar1

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Re: Opposed Piston Engine
« Reply #30 on: September 09, 2013, 10:51:51 AM »
Here's hoping the courts follow through and your daughter is successful in her quest, Gail. And as for your eyes, I'm sure that you will, but follow the dr's orders to the letter, things will turn out OK. We shall all be pulling for you and looking forward to your next installment. Be well and rest up.


best regards


BC1
Jim

Offline AussieJimG

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Re: Opposed Piston Engine
« Reply #31 on: September 09, 2013, 11:05:04 AM »
Take it easy Gail, we will still be here.

Jim

Offline GailinNM

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Re: Opposed Piston Engine
« Reply #32 on: September 09, 2013, 04:51:44 PM »
Thanks for all the comments.

Nick:  The CNC mill is a 29 year old Bridgeport that was CNC from the factory.  One of the first Boss controls to have servo motors instead of steppers.  I bought it new but it's like me and has lots of aches and pains.  Still accurate enough for me however and it would cost more to update it than it would be worth when I finished.  As  long as I keep it tuned up it will turn a circle with 0.001 TIR or close to it. Poor by modern standards but OK for me.

Whiskey:  The end of the crankshaft asay from the headstock is not supported.  That's the reason the order of the cuts is important to keep the set up rigid. Worst case the cutting tool is less than an inch from where the material is supported. I have attached the un-cropped photo of the pin turning operation so you can see the larger picture.

Jim (BC1):  I am confident that every thing is set in the courts.  When the judge says to bring cameras and invite friends it is a good sign.
RE the eyes.  There is nothing that can be done to make them better.  No treatment available for my better eye and for the other eye the treatment only slows down the progression of the deterioration.

JimG:  I will try to post a few simple things when I can along the way. I play the eye doctor game about once a month.  Some times I am only shut down for a few hours and other times it's a couple of days. No way to tell in advance so I assume and prepare for the worst case.

Gail in NM
I would like to be the kind of person my dog thinks I am.

Offline Brian Rupnow

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Re: Opposed Piston Engine
« Reply #33 on: September 14, 2013, 04:18:23 PM »
Gail--This is a fascinating build, and I will follow along. I hope that your eyesight does not deteriorate any farther. Congratulations on your "new" grandchildren. I have 3 grandchildren, two girls and a two year old boy, and they bring a lot of joy to my wife and I.---Brian

Offline GailinNM

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Re: Opposed Piston Engine
« Reply #34 on: September 14, 2013, 04:24:10 PM »
See, I came back after all. Eyes getting worse, but at about the rate expected.  Adoption went smoothly. Photo at:
 http://www.modelenginemaker.com/index.php/topic,2405.msg41247.html#msg41247 

Brian: Thanks for the comments.  I have other grandchildren also. Oldest is 19 and in college in Flordia.

With a couple of parts made, it's time to start making some parts to tie them to gather and build upwards.

The base is just a piece of 0.50 aluminum that is squared up to 5.562 xy 2.437 inches.  The corners are rounded and the top edges got an 1/8 inch radius on them just for looks.  From the bottom, the holes for mounting all the parts were drilled and counter bored for 2-56 socket head cap screws.  The 4 corners were drilled and tapped 2-56 x 0.375 deep to mount the base to the stand when complete.

Gail in NM




I would like to be the kind of person my dog thinks I am.

Offline GailinNM

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Re: Opposed Piston Engine
« Reply #35 on: September 14, 2013, 04:55:33 PM »
The side frames are made from 0.188  6061 aluminum plate.  They were contoured on the CNC mill.  They could just as well be done on a manual milling machine, but I probably would have simplified the shape.

The two frame sides are mirror image of each other except for the 2-56 tapped hole that is sort of between the two large holes at the right end.  The hole on the bottom one is to secure the hall effect device holder for the ignition system and the hole on the top one is the mount for the idler gear to drive the cam shaft.  If you look closely that that hole in the photo you can see that it is in a plug that is inserted in the frame.  I put hole in the wrong position by 0.020 inch when I made the part, so I put a 0.250 diameter plug in to cover up the hole and put a new hole in the plug.

The largest thole is for the crankshaft bearing and the next largest hole is for the cam shaft bearing.  Thew two counter bored  holes are for the mounting screws for the tappet mounting plate that also acts as a spreader for the frames.

On the left is 0.189 wide slot.  This is a slightly loose fit on a 3/16 (0.1875) OD ball bearing which rolls in the slot to act as a crosshead for driving the opposing piston that is away lfrom the crankshaft.  Demands on the crosshead are not very criltical because the connecting rod is so long that it only has a max angle of less than 4 degrees.

In the bottom flat edge, not visible in photo, are three 2-56 tapped holes to mount to the base.



Gail in NM
I would like to be the kind of person my dog thinks I am.

Offline GailinNM

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Re: Opposed Piston Engine
« Reply #36 on: September 14, 2013, 05:59:23 PM »
Now I do a little bit of assembly work to start getting a look and feel of how things are going to look.  I made up two PTFE (Teflon) washers 0.25 OD x 0.16 ID and about 0.03 thick.  Split them with a sharp knife at installed them on the center throw of the crankshaft by twisting them open to slide over the crankpin. The center connecting rod will install between these washers and they will keep the rod from touching the crankwebs.  It should not anyway, but a little extra safety margin does not hurt.

A 3/16 (0.1875) x 5/16 (0.3125) flanged bearing was slid over each end of the crankshaft.  I had left a little radius between the shaft and the crankweb when I turned the crankshaft so the bearingdoes not quite seat against the crankweb.  If I had not left the radius I would have made up a thin washer in installed it so the crank web could not rub against the outer race of the bearing or have turned a small shoulder for the bearing to seat against.
Gail in NM

I would like to be the kind of person my dog thinks I am.

Offline GailinNM

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Re: Opposed Piston Engine
« Reply #37 on: September 14, 2013, 06:45:22 PM »
One of the frame sides is mounted to the base.  The crankshaft with bearing is inserted into the frame side and the other frame side is slid on and fastened to the base. Everything else should be able to be inserted between the sides with them mounted.

Now it looks like I might actually be building an engine.

Gail in NM


I would like to be the kind of person my dog thinks I am.

Offline Dan Rowe

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Re: Opposed Piston Engine
« Reply #38 on: September 14, 2013, 07:14:59 PM »
Gail,
I am watching this with a lot of interest. Very nice work.
It might even get me to think about a model IC engine.

Dan
ShaylocoDan

Offline GailinNM

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Re: Opposed Piston Engine
« Reply #39 on: September 16, 2013, 02:10:05 AM »
Hi Dan,
Glad to have you following along. You always have interesting posts on unusual methods.
I figured that if any IC engine project could interrupt your Shay projects it would be the Gauge1, approx 7/8 scale,  Woolwich  locomotive project that I finished up a couple of months ago.  Lots of fun.  Now back to the current project.
Gail in NM
I would like to be the kind of person my dog thinks I am.

Offline GailinNM

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Re: Opposed Piston Engine
« Reply #40 on: September 16, 2013, 02:34:36 AM »
Now onto things that look more like an engine. 
Junkers and others used a single cylinder with a piston coming in from each end. That worked well for the two stroke engines with ports cut into the cylinder sides for valves.  Not so good for a four stroke with poppet valves.  I drew some various ways up but did not really like any of them.

To simplify the verbal descriptions I am going to refer to the end of the engine nearest the crankshaft as the inboard side and the end away from the crankshaft as the outboard side.cylinder

With The design I ended up with inboard end looks just like a side valve single cylinder engine.  But instead of a head, another cylinder (the outboard cylinder) is mounted in line withe the first cylinder.

The two cylinders are almost the same.  The only differences are the location of the oil cup hole and the mounting holes. 

The oil cups are offset from the center line of the cylinder.  On the inboard cylinder it is to get them out of the way of the valves and tappets.  On the outboard side it is to gove more clearance to the end of the sparkplug to reduce the risk of sparking to the wrong place.

On the outboard cylinder the mounting hoses are 2-56 clearance through all the fins.  On the inboard cylinder the holes are tapped 2-56 and only go in a short distance from the cylinder mount end.  The mounting screws go through the outboard cylinder, both cylinder mounts and thread into the inboard cylinder flange so the whole mess is clamped up. There are assorted orings and gaskets involved also.

Gail in NM
I would like to be the kind of person my dog thinks I am.

Offline V 45

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Re: Opposed Piston Engine
« Reply #41 on: September 16, 2013, 02:44:14 AM »
Hi Gail,
  Looks great so far. Looking forward to the runner. Keep up the great work !!
  Dave
Never assume the implied task has been completed !!

Offline GailinNM

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Re: Opposed Piston Engine
« Reply #42 on: September 16, 2013, 02:50:37 AM »
The cylinders are made from cast iron.  I use standard one inch nominal bar stock from the metal suppliers.  It is often sold as Class 40 or grade 40.  Nothing really special about it.  As purchased it measures about 1.05 diameter to allow cleanup to the nominal size, which I do so it will fit into a one inch collet.

A stud 0.437 diameter is turned on the end that will locate it in the cylinder mount and hold the o-ring seal that keeps the good things than make power in the cylinder.  Enough of the bar is turned down to the finished cylinder diameter of 0.984 to make one cylinder. Then the fins are cut with 1mm thickness and 1mm spaces.  Each end has s thicker section to support the mounting bolts and threads.
Photo shows the blank ready for cutoff. Then the second cylinder was cut the same way.
Gail in NM


I would like to be the kind of person my dog thinks I am.

Offline GailinNM

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Re: Opposed Piston Engine
« Reply #43 on: September 16, 2013, 03:03:01 AM »
Thanks Dave.  It will get there slow but sure.

Changing collets, the cylinder blanks were center drilled, drilled and bored to 0.3735 or so to leave about 0.0015 to 0.0010 stock left for lapping.  The acutal size is not really critical, but targeting a dimension like this lets me use an old carbide end mill shank as a plug gauge.  They are typically 0.0001 to 0.0002 inch undersize. I will explain why this is nice when I get into lapping the cylinders.

Gail in NM


I would like to be the kind of person my dog thinks I am.

Offline GailinNM

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Re: Opposed Piston Engine
« Reply #44 on: September 16, 2013, 03:44:34 AM »
One side of each cylinder has a flat milled. The valves are located in this flat area on the inboard cylinder and the spark plug in the outboard side. The oil holes are drilled into the cylinder bores and then opened up to fit the oil cups. This defines the inboard and outboard cylinders as the holes are in different locations.

Gail in NM

I would like to be the kind of person my dog thinks I am.

 

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