Stothert and Pitt in 1/6th (and other) scales

[Jo]

Amongst the many models I am making are two models of my University's Beam Engine, the Stothert and Pitt which was exhibited at the 1867 International exhibition in Paris:



Today she is living under the stairs in one of the buildings at my University, the University of Bath. My plan is to make two versions of this engine: The smaller version of the model (1/12th scale) is being made using of a set of ?castings? from Anthony Mounts build of one of these engines, which I expect to be heavily modified and the larger one (1/6?) scale which is being scratch built. Anthony took a lot of liberties with this engine to simplify it and it is my intention to try to make my model a lot more like our original engine.

I have already knocked up the columns and the table:



And started on the beam pivots:



And the flywheel:



And using some come in handies am making up the cylinder for the larger engine (the cylinder material for the smaller one is in the front of the embrionic larger engine cylinder of this view).



I hope you don?t mind but I have started this thread early so that I can first pick your brains .

Jo

[tel]

Nice going Jo - I have the S&P drawings, but haven't steeled myself to start a build yet.

Knocked up the columns and the table? Pure art there matey, lovely stuff.

[Jo]

Here is a picture of our engine, sitting as she is today lost and forlorn under the stairs:



I have an extensive set of photo photgraphs and measurements of her which I intend to bring to the party over the build.

Jo

[Jo]

The columns on this engine are gently tapered with square bases and some very interesting capitals. The columns were machined in three parts the square base came out of a piece of square material, then I turned up a length of brass to give the ?bulges? at the bottom of the column and finally the columns are a simple taper turning exercise that I cheated and did on my Colchester using the taper turning adapter. Having made these each was then mounted on the dividing head with tail stock support and slits cut down the length of one side to take the gusset plates.

The gusset plates on the smaller commercial engine set are provided as a pair of water jet cut parts, the intention being to simply clean these up with a file and Bob?s your uncle. However on the real engine these gusset plates have a flange on the inside that looks like this:



On my 1/6th scale engine I added these flanges by soft soldering a piece of 1/8? brass around the inner surface of the gusset plates like so:



Now for the first challenge: you cannot help but have noticed those beautiful capitals, just in case here is the view from the outside of the engine



I am looking for suggestions as to how to make these, I am assuming that the square tops will be separate parts .
-------
Tel: nice to hear of another S&P intended build.

Jo

[tel]

Just thinking about those capitals makes my brain hurt. My only suggestion would be to persuade our old mate Abby to cast some.

[Jo]

No, no , no that is cheating, and I would still need to make the first one. Once I have made one then the other 3 should not be a problem (then I only need to do it again at half the scale ).

I had been thinking about making it in two parts: the first part would be the lower bit that looks like a group of leaves going upward and then a second that fitted into the top which provided the diamond shapes in between the leaves. How to make these is still a challenge .

Jo

[Jasonb]

I've known you had these on teh go for some time, nice to see them break cover.

As I was reading your post I had the same thoughts as Tel about Abby, though that still leaves how to make a pattern.

I've recently seen some nicely cast parts from 3D printed patterns so if you could draw them up in cad that would be one way.

To fabricate either a master to use as a pattern or four individual parts I wonder if a piece of copper tube could have the leaf shapes cut out with a piercing saw and then gently flare them out over a former. You would probably need two concentric tubes, one for the gold leaves and another for the red. These could then be soldered to a core, the bottom bead done as a round edged washer and the top as you say just a square.

J

PS how do you intend to replicate the cob webs?

[Jasonb]

Looking again you could possibly also do the leaves by turning a flared trumpet shape and then cutting the leaves again with a piercing saw.

I don't feel casting is cheating provided you make the pattern, now a simple RTV mould and some resin would allow you to cast them at home if you want to do it all yourself, add some metal filler powder to the resin and it will be like the original cast iron ones

J

[Jo]

The original ones are brass.
 
The flared trumpet was my original thoughts, then putting it on a dividing head and cutting the leaves using a sort of profiled flycutter.

Jo

[Jo]

PS how do you intend to replicate the cob webs?

It is sad they don't look after her. The quality of the paint is just as poor she has clearly been painted, chipped, repainted etc, none of it is smooth. In fact it looks just like my painting .

Jo

[b.lindsey]

Jo,
Imagine a piece of suitably sized square brass laid on its side....then milling the upper contour parallel to each edge about 1/2 to 2/3 down each side to preserve the corners which show between the leaves there at the top. Then using a 4 jaw chuck, turn the lower portion round blending in to the squared portion again 1/2 to 2/3 down from the top of each capital. Finally cut, stamp, or otherwise machine the four identical leaves and soft solder them to the four sides.  Maybe I am not seeing everything dur to the glare on the brass in the pictures, but it seems like a possibility to me.  If I can scratch together a CoC sketch I will try to post it.

Bill

[tel]

Yep, CoC please Bill, but - I think there are are least 6 'leaves' on each one, not 4.

[b.lindsey]

Here's a quick CoC sketch. Six leaves would complicate it somewhat for sure but could still be done I think by soldering the bottom of the leaved to the circular part of the base.

[steamer]

I was thinking maybe something along the lines of cutting a gear.    If you were to break this up into 3 parts.....tedious yes...but you could use it as a pattern for a cast part....

The first part is the lower section with the round base and 6 leaves (?)  Turn the trumphet shape in the lathe with a form tool.   

Now hollow out the back with a conical cutter....now it really looks like the business end of  a trumphet!

Next ....the outer row of leaves

Make up a fly cutter shaped much like a gear tooth profile....and the final shape would be by cut and try mind you....and indexing the part about its circular axis, cut "teeth" into it.   The combination of the trumpet shape and the "gear tooth" shape should give you that leaf shape on the outer row.

NOW for the hard part......

Cut another conical section piece, and with a different form cutter, cut another cone....that fits in side and meshes with the first.....showing the "shadowed" leaf.  It would be made very similarly to the first part and would definitely need some hand fitting.....but would fit together like a spline.

NEXT ....make the square capital top and soft solder (epoxy) the threee pieces together.   The fact that you have the central post would do well during assembly

You could then cast this up and machine in the usual way...

Dave

[b.lindsey]

Thinking more on this....if there are in fact 6 leaves then what if you took hex brass stock and coutoured it on the lathe so that the hex edges remain at the top portion and gradually fade away nearer the bottom as the trumpet contour is turned. Would still leave the defined corners at the top between leaves. Then simply soft solder a square brass cap to the top.  Actually might be simpler than doing it with square stock to start with. This assumes that the leaves would be made separately still and soldered using the remaining hex edges as a guide.

Bill