Arnold's take on the MEM Corliss

[swilliams]

Fantastic Arnold, she's going to come up a treat with all the finishing touches and already runs great.

Congrats
Steve

[arnoldb]

Thank you all for your kind replies 

Bob:

And that my friend is proof positive of your skill as a model engineer.

Bob, thank you, but I don't consider myself skilled.  There has been a lot of learning during this build, with more to come. 

I cannot say how much it means to see the successful fruit of our labours in the flesh.

Me too - Thank you and the rest of the team  - the least I could do to contribute beyond yapping about metric sizes and complaining about small screws was to at least build it to prove that all the design work was worthwhile, and it really is.  I used all the essential dimensions as-is, and that is now proven to work well, so anybody else building the engine can rest assured that all the core dimensions are correct to build a running engine.  As Jerry mentioned, that's what it was designed to do, so here's three cheers to the design team  . 

Jim, yes, I'll definitely give the governor a go; I first want to get the engine looking a bit better though - there's some bits that need re-making and all the paint work, and I do need a small break to sort out the shop a bit as well... 

Eric, a speechless redneck ???? - I've never seen (or heard) that...  Some moonshine will cure it double-quick - just make sure there's no FDA's about 

Phil, yes; it is extremely satisfying.  At a quick count, this is my twentieth engine, and the thrill of seeing an engine's first run never diminishes. 
The MEM Corliss can run in either direction simply by rotating the eccentric through 180^o.  In fact, at final assembly, I'll make this one run the other way - simply because with the rotation as-is currently it will be inclined to loosen the crank screw over time, especially if there's a little friction there.  In fact, it will be very easy for other builders to make a slip-eccentric to make it run either way 

Kind regards, Arnold

[vcutajar]

Well Arnold you made my day yesterday when I saw your Corliss actually running.  It gave me a gaol to aim to. I am still way behind you in my build but slowly I will get there.

Vince

ps. What is a slip eccentric?

[Maryak]

Hi Vince,

The attached PDF explains slip or loose eccentric better than I could.

Hope it helps.

Best Regards
Bob

[ReFlad]

Effen awesome Arnold!  I am not surprised that it runs so well without all of its parts.  It shows what type of craftmanship built it.  Great build.  Great Engine.  Very enjoyable!

Ronald

[arnoldb]

Thanks Vince, Bob & Ronald - my apologies for the late reply.

I've had a couple of enquiries regarding the mention of a slip-eccentric.  In addition to Bob's picture, I'll do a little write-up in another post on one I've made; it might be useful to see photos and a short video of it working.

There's been zero progress on the engine, and most likely I'll only get to work on it in about a week and a half's time again.  From here, updates will be a bit slower.

Kind regards, Arnold

[arnoldb]

Well, the week and a half turned into more than a month and a half...

Yesterday I took some time from a very hectic schedule, and messed up the shop a bit.

I never got around to making the valve bonnets, so I started off with strips of 1.2mm brass plate for the rear valve bonnets.  The plans call for 1.5mm, but I don't have any.  As the insides of the plates will be subject to air/steam pressure, these cover plates can not be too thin, but 1.2mm over the 15mmx15mm area is well within safety limits for a working pressure of 60psi:


One strip was squared up and brought to 15mm width, then I started to drill holes in it.  The first holes was a booboo - I drilled them 0.5mm too close to the end...:


So I used the second row of holes as a new starting point, and drilled all the holes for the covers, leaving enough space in between each set of four to saw off the covers:


Once sawed apart, I just used two drills through the holes to clamp the lot together to mill the sawed sides to size:


The plates were still a bit rough-looking:


That was easily taken care of with a quick flat-rub on some 600 emery:


On to the front valve bonnets.  I've been looking around for some 15 or 16mm square brass bar, but have been unable to find any.  I have about 300mm of 25mm square brass, but making them from that would be a bit too wasteful at the going rate of brass.  What I did have floating around was an 8mm thick slice of 50mm square bar end:


After a quick head-scratch as to how I could make that into the bonnets, I settled on a plan of attack.  First was to bring a suitable section of it down to 6mm thick:

It wasn't clamped on by much, so I took things easy with many light cuts.

The thinned section was sawed into two strips; those were then milled to the needed 15mm width.  I then set up the vise back-stop, located the end of the workpiece, and from there the center of what would become the first bonnet.  Then I drilled all the holes.  Scratching around my stock of O-rings, I found the thinnest 3mm ID ones - they have a 1.5mm thickness - so I used a 6mm slot mill to counter-bore 1.4mm deep:


The rest were easy to do; rotate the part 180^o to make the other one - using the stop to locate it, and repeat for the other strip.Then saw them apart:


And clean up the sawed edges - once again using drills to determine the height for quick workpiece rotation:


To turn the spigots, I just faced a bit of aluminium scrap in the lathe, and with a bit of cardboard set things up for friction drive in the lathe:


Turned down - with light cuts and a sharp tool so as to prevent jam-ups:


The others followed, and I ended up with this lot for the shop session:


Somehow a small cup-fed HVLP spray gun followed me home a while ago.  I guess it's time I started to "play" with it...

Kind regards, Arnold

[steamer]

Nice job on the bonnets Arnold.   

Dave

[Don1966]

Nice job on the bonnets Arnold.   

Dave

What Dave said, I like your technique.

Don

[vcutajar]

Good job on the covers Arnold.  I'm still stuck with the cylinder feet.

I see you are using an O ring in the front covers as per plans.  If I use a gasket instead of the O ring do you think I can get away with it?

Vince

[Maryak]

Hi Vince,

Th O ring is to seal the valve shaft. I'm not sure a gasket will do that.

Best Regards
Bob

[vcutajar]

Thanks Bob.

In that case a gasket will not do.

Vince

[Captain Jerry]

Arnold

That is a nice looking set of bonnets.  In my experience, this is a critical step as it affects the free rotation of the valve.  You have allowed for a .1mm compression of the O-ring but I am not certain how the seal functions in this design but it seems that as the front and rear bonnet are tightened, the O-ring is compressed between the shoulder of the valve and the bottom of the bore in the bonnet, sealing on the face of the shoulder as well as sealing against the reduced shaft diameter as the ID of the O-ring is reduced by compression.

There are a number of critical dimensions that have to match up, including the thickness of the cylinder block, the length of the valve body, the depth of the bonnet bore, the thickness of the O-ring, and the thickness of any paper gaskets between the bonnets and the cylinder block. If there is too much compression of the O-ring, the amount of force needed to rotate the valve can be excessive.  You can create the same problem by over tightening a piston rod  or a valve rod gland, but that is easily overcome by the force of the piston or the eccentric linkage but it reduces the efficiency and performance of the engine.  A little extra friction on the exhaust valves of a Corliss engine is also overcome by the eccentric linkage.

The steam valves are a much bigger problem if you intend to include the trips.  When the release trips, the valve is disconnected from the eccentric and the only force acting to rotate the valve is the dash pot.  Not much force at all.  You can increase the weight of the dash pot or the spring but that makes the release point less reliable.  It is a two edged sword.   If the dash pot can't rotate the valve, you don't have a working Corliss valve.  If the release doesn't trip reliably, you don't have a working valve either.

In addition to the seal friction, the bonnet bore must be concentric with the valve bore and since there is no spigot for registration, that leaves the four bolts to control the position.  The cheap digital scales on my mill are certainly not perfect and getting the four holes of the bonnet to register perfectly with four holes on the cylinder block is a challenge that usually requires over sized clearance holes in the bonnet.  I have had valves that turn freely, lock up solid as the last bolt is tightened.

I hope you don't mind me pointing out the difficulties that you are facing.  You are probably already aware of them and I am sure that you can deal with them and produce a working engine, but most viewers may not be aware of them and therefore not able to appreciate the challenge you are facing.

Get your fiddle tuned.  You're in for some fine fiddling.

Jerry

[swilliams]

Good stuff Arnold, nice to see you back at it 

Steve

[NickG]

Yes nice work Arnold, still watching.