# Wobbler timing by Tubal Cain



## Two Blocked (Feb 22, 2008)

I just read a small book authored by the British model engineer Tubal Cain entitled "Building Simple Model Steam Engines". It is still available through Amazon, and it describes the building of four, quite small, oscillating engine/boiler plants. His style is reminiscent of that of LBSC insofar as he wastes no word, but rather gets straight on with the job of making parts that will do the job simply and elegantly.
One way that Mr. Cain economizes information is to use the same engine design for all four engines. I am reproducing the generic valve timing diagram that he published on page 40 of his text below.










The crank angles are unusual to my experience because of the 90 degree angle demanded by the drawing between the connecting rod position at full admission/exhaust with regard to a line drawn through the centerline of the crank disk. My usual experience is that the crank positions, at the extremes of motion, are on the horizontal centerline of the crank/disk. 
I am asking the Live Steam Forum in general if anyone else has come across such a valve diagram, and what kind of an oscillating engine demanded it. Lacking that, or maybe better yet, what is the mechanical imperative of such a valve diagram. Theories are more than welcome because they are based on something [practice, mechanics, etc.]. Opinion, not so much because everyone has one, and facts are not required.


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## Two Blocked (Feb 22, 2008)

Posted By Two Blocked on 31 Aug 2012 03:24 PM 
I just read a small book authored by the British model engineer Tubal Cain entitled "Building Simple Model Steam Engines". It is still available through Amazon, and it describes the building of four, quite small, oscillating engine/boiler plants. His style is reminiscent of that of LBSC insofar as he wastes no word, but rather gets straight on with the job of making parts that will do the job simply and elegantly.
One way that Mr. Cain economizes information is to use the same engine design for all four engines. I am reproducing the generic valve timing diagram that he published on page 40 of his text below.










The crank angles are unusual to my experience because of the 90 degree angle demanded by the drawing between the connecting rod position at full admission/exhaust with regard to a line drawn through the centerline of the crank disk. My usual experience is that the crank positions, at the extremes of motion, are on the horizontal centerline of the crank/disk. 
I am asking the Live Steam Forum in general if anyone else has come across such a valve diagram, and what kind of an oscillating engine demanded it. Lacking that, or maybe better yet, what is the mechanical imperative of such a valve diagram. Theories are more than welcome because they are based on something [practice, mechanics, etc.]. Opinion? Not so much because everyone has one, and facts are not required.


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## Two Blocked (Feb 22, 2008)

Posted By Two Blocked on 31 Aug 2012 03:26 PM 
Posted By Two Blocked on 31 Aug 2012 03:24 PM 
I just read a small book authored by the British model engineer Tubal Cain entitled "Building Simple Model Steam Engines". It is still available through Amazon, and it describes the building of four, quite small, oscillating engine/boiler plants. His style is reminiscent of that of LBSC insofar as he wastes no word, but rather gets straight on with the job of making parts that will do the job simply and elegantly.
One way that Mr. Cain economizes information is to use the same engine design for all four engines. I am reproducing the generic valve timing diagram that he published on page 40 of his text below.










The crank angles are unusual to my experience because of the 90 degree angle demanded by the drawing between the connecting rod position at full admission/exhaust with regard to a line drawn through the centerline of the crank disk. My usual experience is that the crank positions, at the extremes of motion, are on the horizontal centerline of the crank/disk. 
I am asking the Live Steam Forum in general if anyone else has come across such a valve diagram, and what kind of an oscillating engine demanded it. Lacking that, or maybe better yet, what is the mechanical imperative of such a valve diagram. Theories are more than welcome because they are based on something [practice, mechanics, etc.]. Opinion? Not so much because everyone has one, and facts are not required.


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## Phippsburg Eric (Jan 10, 2008)

Interesting! His drawing is probably the "correct" way but the geometrical difference is negligible. laying out the ports using the 90deg crank angle as you have done before should yield ports just slightly inside of those laid out his way giving steam for slightly more of the stroke....if you drill your holes accurately!


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## HMeinhold (Jan 2, 2008)

Try the Dockstader program:

http://www.billp.org/Dockstader/ValveGear.html 

SimpOsc is the valve gear you want. I had problems with the engine of my Guinness, so I played around with this program and found out, that the port openings were too small, leading to some compression at the end of the stroke. By the way, the oscillator is in zip file "E", which is not listed in the directory, but in the downloads. If in doubt, download all and run Vgstart.
Regards


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## Steve Shyvers (Jan 2, 2008)

Kevin, 

I'll hazard a hypothesis. I haven't seen this valve diagram before, nor have I consulted Dockstadter. 

With Cain's layout as shown the steam admission port is fully open earlier in the admission stroke than if the cranks had been on the horizontal center line to do the layout. This gives maximum amount of steam before the crank is at 90 degrees where it will transmit the maximum torque to the crank shaft. It will also close earlier which allows a small amount of expansion toward the end of the stroke. At the early part of the exhaust stroke the exhaust port is closed when the steam will be condensing and reducing in volume. Then when the exhaust port does open it will be fully open later in the exhaust stroke when the cylinder needs to expel its condensate. 

Now I have to think about whether Cain's valve diagram would have a bigger impact at slow speeds or high speeds. 

Steve


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## Two Blocked (Feb 22, 2008)

HI Steve; I'm still working this issue too. I'm also thinking of adding a port to the cylinder design, just above the piston top, to "scavenge" the cylinder at bottom dead center. I did this awhile back to a piston valved, single action, fixed single cylinder mini-engine [think a small "Cricket" copycat] with vavooom results. The scavenge port spit a pot full of condensate. If I ever do it again I'll make an annular exhaust of some kind to catch the "dead steam" [Sand Pebbles; Steve McQueen]. 
In my late teenage years I was a daily commuter on the Staten Island Ferry. I spent nearly each "passage" in the machinery spaces [imagine that today!], and I was particularly fascinated with the Skinner Uniflow single expansion steam engines that drove some of these ferries. The Uniflow engines received steam from the boilers that powered the single acting pistons, and at the bottom of the stroke exhausted the waste steam and condensate via cylinder scavenge ports into the vacuum caused by the sea water cooled condensers. The return stroke to top dead center was not a compression stroke because the cylinder was full of "nuttin", and it had an atmosphere of crankcase pressure per square inch driving it up. 
In our hobby there is a historical figure, Larry Lindsey (sic) of Denver, CO. He and another gentleman (?) were the manufacturers of the Lindsey Shay. I'm pretty sure that Marc featured this Shay in his monthly review of unique locomotives in GR. As I remember Larry made some sketches of such a simply scavenged single acting engine and they were published in an early precursor [Side Street Banner Works] to GR. I don't know if anyone other than I ever tried the idea out. I'd sure like to know.


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## xo18thfa (Jan 2, 2008)

That diagram shows the maximum deflection left and right that the cylinder goes during its stroke. You see that in the triangle formed by the cylinder pivot point, the 90 degree angle and the center of the crank. The distance from the 90 degree angle to the crank is half the stroke of the engine. From that you can locate the exhaust and steam ports on the cylinder port face. Determine the diameter of the port openings so that both steam and exhaust are closed exactly at TDC and BDC. If the ports are too big steam and exhaust over lap. at TDC and BDC. If the ports are too small the engine is inefficient.

That diagram is the "holy grail" of simple oscillator geometry.

The trick Tubal does not show is how to use that diagram to make a simple drill jig to accurately locate the ports. Something like this:


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## Steve Shyvers (Jan 2, 2008)

Hi Kevin, 

I remember you describing the scavenging port several years ago. Even without a scavenging port a simple single-acting wobbler such as the Midwest engine used on the BAGRS loco dumps a lot of condensate onto the deck under the cylinder when running, so all the condensate doesn't need to get pushed out the exhaust port. Those are tiny, low-toleranced, low-pressure engines, so they will have a lot of condensate, which probably helps to seal the piston also. 

I was fooling around with a "steam motor" design that had two single-acting cylinders side-by-side and set 180 degrees apart on the crank. It would use the scavenging ports as you described to exhaust the condensate. The hope was that I'd get the same performance as a double-acting single cylinder but with much simpler piston/cylinder construction. The tradeoffs would be that there would be more mass of metal to keep hot for the same amount of steam and the two cylinders would have twice the amount of sliding surface area, hence twice the friction. Haven't built a prototype yet. 

Steve


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## Ger  (Jan 13, 2009)

I built the Coles' Power Models "Twin Cylinder V Oscillating Engine" from their plans and castings. The plans include a drilling jig for the cylinders and standard. The jig is necassary to build the engine. This was a very interesting engine to build. The engine has many drilled and plugged steam passages. It has a built-in reversing valve and is self-starting since there are no dead centers. It runs very good. 

A word about Tubal Cain. He real name was Tom Walshaw and he used the pseudonym "Tubal Cain". According to Wikipedia, he wrote over 424 articles for "Model Engineer" magazine and also published many books on model engineering. (The real Tubal Cain is credited with inventing metalworking. He was a decsendant of the Biblical Cain.) 

I am supprised that a drilling jig was not shown in the book. His books usually include many drilling and turning jigs. I built a twin cylinder compound engine using his plans for jigs. This was detailed in his book "Simple Workshop Devices". I could have not finished the engine without these jigs. I have several of his books and they are very informative. I would surely trust his drawings to be correct. 
Gerald Pierce


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## Finster (Feb 7, 2009)

You may already know but I believe the author Tubal Cain has a Youtube channel with some nice machining/casting videos and tips. This may also be a way of contacting him regarding the book and jig, (if you wanted to)
His Youtube channel name is mrpete222. http://www.youtube.com/user/mrpete2...sults_main At least I think it's the same guy, although I could be wrong. Hope this helps.


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## steamboatmodel (Jan 2, 2008)

Posted By Finster on 02 Sep 2012 04:11 PM 
You may already know but I believe the author Tubal Cain has a Youtube channel with some nice machining/casting videos and tips. This may also be a way of contacting him regarding the book and jig, (if you wanted to)
His Youtube channel name is mrpete222. http://www.youtube.com/user/mrpete2...sults_main At least I think it's the same guy, although I could be wrong. Hope this helps.
You are wrong, Its not the same guy by a long shot. The Book and the articles published by the British model press were done by Tom Walshaw. http://en.wikipedia.org/wiki/Tom_Walshaw 
Regards,
Gerald.


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## Finster (Feb 7, 2009)

Ok, thanks for the info. I wasn't sure if it was the same person or not. I only knew the name Tubal Cain not the original author and this guy usually starts his videos by saying 'Hi, Tubal Cain here...' or something similar. Even if it's not the same guy his channel is worth a look see...


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## steamboatmodel (Jan 2, 2008)

Tubal Cain. The pseudonym relates to the eponymous biblical metal worker.


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## xo18thfa (Jan 2, 2008)

There is a guy doing video's on YouTube copying the name Tubal Cain. The real model engineering pioneer "Tubal Cain" was Tom Walshaw.


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## John Riley (Jan 3, 2008)

Hello Kevin 

I am building a version of Hank Povee's 4-2-0 "One Arm Billy" a circa 1837 Norris engine which I am setting up with single acting oscillating cylinders set at 180 degrees. I think your scavenging valve set up would be a worthwhile modification. What size scavenging port did you use on the "Cricket style" engine, also what was the piston diameter? I have built a couple of engines powered by ossies based on Tubal Cain's books, but thanks to Larry Herget's wise advise I made myself drilling jigs to get consistent spacing for trunnion, axis crank axis, and steam and exhaust ports. A few years back Mike Martin did some work on varying port sizes on oscillating engines. He also developed an oscillator simulation program which you will find on his Modern Steam web site, it is well worth a look. 

Cheers,

John Riley


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## Two Blocked (Feb 22, 2008)

Hi John, Bob, and Gerald, 

I could not find the tiny wobbler I spoke of, and I'm thinking that I gave it away at a Diamondhead seminar way back in the late "90"s, but not to worry, I did find a reference to it in my shop notes from 1997. The cylinder was turned from a piece of 1/4" drawn yellow brass and the ID was either 5mm or 3/16". It looks like I went for a 1" stroke, although 3/4" could have been the real number. When I got around to the scavenging port, I did not drill a hole(s) in the side of the cylinder, but rather I hacksawed a slot up from the bottom of the cylinder skirt [through both sides] to just the top of the piston at TDC. I was running the engine off of my donkey boiler during the experiments, and little by little I coaxed the slot deeper till condensate started to trickle out of the slots. Maybe .010" deeper I started to see some weak steam too, and by .020" the cylinder appeared to "empty"." Each time I ratcheted the slots up, the engine became livelier, and then as I continued, the speed fell off. I am guessing the optimum opening (2) was the width of a 32 tooth hacksaw blade [.030 to .040"] by .015" to .020" deep. 

If I did this trick again I would include some kind of annulus drain affair around the cylinder to catch the condensate and direct it downward, as the little imp was a messy affair on the bench 
. 
I too believe strongly in the advantages of drill and other jigs, but I tend to limit their use to production operations. I used jigs to machine and silver braze the first few Cricket boilers, and to make Hadden Valves and Unit Shop Gas Valves, and just a few months ago threaded drill bushings for the Accucraft Shay exhaust steam pipe conversion. For onesees and twosees I jig drill parts on my Sherline mill. My standard operating procedure [SOP] is to make up an X-Y coordinate sheet with hole positions and diameters identified. For something complicated like double acting wobbler port positioning, I routinely lay out a ten or twenty to one enlargement, and then pick off the centerlines with a Starrett machinists' scale graduated in .010 of an inch as X-Y coordinates. Sherline mills are potent in the hands of a skilled operator, and X-Y positional dimensions of plus-minus .002" are quite possible. 

The above mentioned Larry Lindsey also had a way of spicing up wobbler performance. His trick was to magic-mark the port faces of the engine and then to mark them as squares around the valve opening holes as normal to the pivot pin center. The next step is to Swiss file the holes square [just at the face, say .010" deep at a slight angle] so that the valve holes will "snap" open as they pass each other rather than slooowly open as round ports are wont to do. I have done this to Mamods and "Janes" with noticeable results in tractive effort, and I would plan ahead to include it in any future wobblers that I construct.


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## Skeeterweazel (Feb 11, 2014)

Does anyone of a copy of the diagram from post #1?
Thx.

Edit: that is a great program w/ all the valve arrangements. Looks like oscillators can make good power, but use a lot of steam.


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