Tertium Quid

[ProdEng]

I am looking at drawings for Stan Brays Tertium Quid but having difficulty seeing how it can go together. Does any one have any experience of this engine?

Jan

 

[steamer]

Without publishing prints.....do you have a picture?......Im not familiar with that engine,,,


Dave

 

[ProdEng]

It's an inverted vertical single similar to a Stuart Turner No 1. The design was published in Model Engineer 20+ years ago and then again in The Best of Model Engineer Vol 2 in 2010. The drawings are full of errors, hence nothing lines up. It doesn't matter much as I am building a 3D model and will make lots of changes anyway. It just puzzles me that the design has been around for so long and I can find no sign of anybody having ever built one.

Jan

 

[Tin Falcon]

Jan: this is the first time I have heard of that engine as well. but if insprided a stuart degign sounds interesting. I think you answered your own question . if the plan is riddled with errors there are probable more failed attempts out there than people want to admit to. redrawing is always a good idea get the design in your head and sodid modeling should get the kinks out . looking forward to seeing what you do with this one.
Tin

 

[ProdEng]

Tin, this is going to be a clear case of ambition overcoming experience so should be good for a laugh! The model should be done soon so we can start cutting some metal.

Jan

 

[ProdEng]

After two days of unraveling this design I have lost confidence that it could work. The valve rod is connected directly to the eccentric without a joint forcing the valve rod to bend to accommodate sideways movement. The valve rod also has a kink in it to make up for the fact that the hole in the steam chest for the valve rod and the eccentric are not in line. The strange thing is that there is ample room to move the main bearing over to achieve alignment.

I like the basic design but need a lot more experience before I could hope to sort it out. Grafting on an Elmer's cylinder would most likely solve a few problems so I should build the Elmer's engine first!

Just for interest I have attached the model so far. Note that there is no hole in the base plate for the eccentric, another "feature" ;D

 

[Captain Jerry]

Jan

That is a nice looking engine and a nicely done model as well. Since it seems that you are working with some questionable dimensions and details from the original your model will have to be the deciding plan.

1. Eccentric rods don't bend without a joint. You can design that easily or copy a design from almost any similar engine. They all have one.

2. Don't worry about the offset bend in the rod. That is also common. A few years ago, I expressed my fear of bending a valve rod and getting it right. Several members here gave me the necessary kick in the pants to get me over that. Now, having done that several times with no ill effects, I urge you to do the same. Easy peasy.

How big (or small) is this engine, Bore? Stroke?

Good luck with the project. I would like to see it built.

Jerry

 

[Ken I]

Hi Jan - the name of my company is Productive Engineering which I frequently shorten to Prodeng - coincidence ?

I am curious about a design "riddled with errors" - in my commercial machine designs I supply a full set of drawings to my customers with a caution that some of the major elements (that would normally not ever need to be replaced) contain fundamental errors which will render them useless and they should contact me if they ever need to make anything from my drawings.

This is to discourage the use of my drawings to build new or replacement units from my plans without me getting a dime.

Those that have tried have learned it is cheaper to pay for my intellectual property than to steal it.

Don't worry eveything I post on HMEM is free of deliberate errors.

However I wonder if these plan errors are not deliberate for the same reason. Perhaps if you buy the original plans it comes with an erratum list for you to pencil in - anyone simply copying a drawing is going to end up in trouble.

Any other model builders that have come across this sort of thing ?

Good luck with the project.

Ken

 

[ProdEng]

Jerry,

I will attempt to graft on one of Elmer's cylinders as the scale is about the same, 1/2" bore and 3/4" stroke. Elmer's designs are reliable so that will give me some confidence. The bottom end of the engine seems to work quite nicely in the simulation in Inventor.

Ken,

ProdEng is for Production Engineer, my occupation for the first seven years of my working life. I was involved with the development of machining processes and great fun it was. With the imminent collapse of the British engineering industry in 1979 I moved to electronics, started my education all over again, and stuck with that for 22 years. Now I have gone full circle and am doing a production engineering role albeit in the plastics industry.

As for the engine design, it is a published design with a construction article and I expected more from Model Engineer.

Thankyou both for your comments, it has broken my sulk and I will now continue ;D

 

[ProdEng]

With a bit more effort and a little luck I have now resolved all the major issues with the design and some parts can now be made. Still a bit of detail work needed and doubtless changes will be made along the way. Picture of latest version attached.

 

[Brian Rupnow]

As an unsolicited suggestion---Why not get rid of the vertical grey support rod and just mirror the green vertical support about the nominal centerline of the cylinder? It would give the engine a much more aesthetic balance.---Brian

 

[b.lindsey]

This reminds me of a new/old design reintroduced by Tiny Power 5-6 years ago based on a 1926 design by H.J. Coventry (according to their information). I had bought a couple of the casting sets at the introductory price but found some of the castings (patterns) to be badly misaligned. I did complete one of them and it ran reasonably well. The remaining casting are gathering dust at the moment. I guess this was a populare design back in the day.

http://www.tinypower.com/store.php?crn=56&rn=175&action=show_detail

Bill

 

[Captain Jerry]

Jan

That is looking good. I think your first crosshead design was better but that's just me.

It would be nice to be able to see this design from different angles. I'm not familiar with Inventor. Can it export a 3D .pdf file like this cast elbow which was done with Alibre'. It will let you rotate the object in space if you activate the 3D option by clicking in the upper left corner of the drawing.

I know it is asking a lot but it would make it much easier if I decide to emulate, copy, steal, learn from your work.

Jerry



View attachment cast elbow.pdf

 

[ProdEng]

Brian,

The idea of using the stay is to expose all the workings of the engine. I am certain the original working engines where made this way to save money

Bill,

Little Kathy is very similar to mine and about the same scale. Mine will be all bar stock so lots of machining and handwork.

Jerry,

I have never tried any animation, I use modelling as the fastest way to produce a set of accurate working drawing. Inventor creates dimensioned drawings in a few minutes along with sections and anything else you desire. There will be a full set of drawings by the end of the project, assemblies and parts, as I seldom work without them.

Jan

 

[steamer]

Brian,

The idea of using the stay is to expose all the workings of the engine. I am certain the original working engines where made this way to save money ......

Nope....made that way to make it easier for the engineer to get to the moving parts. The thrust bearings of the crossheads were optimized for forward or ahead which turns the crank clockwise while looking at the crank from the propeller side. The load on the crosshead was always the same direction. In astern or reverse, the otherside of the crosshead bearing had to take the load, but considering it didn't have to do it for long, the bearing area was usually reduced.
The ability to get to the crosshead and conrod bearings easily was very important and useful.
The last thing you want in ship is an engine built to the lowest price.

Here's evidence to this point

Dave

 

[ProdEng]

Thanks for the explanation Dave, makes it easier to see why the engine was constructed that way. I would like to read more about steam engine design and have one book on the way. Can you recommend a good read?

 

[steamer]

Oh a couple of dozen!

Cecil Peabody, "The thermodynamics of the Steam Engine" comes to mind

I am sure you can find that on google books

Dave