This is the drawing that was originally on ME issue No 49

Thanks for the comments, Luker I will wait for my paper copy to have a read of your 3D printed pattern article.

It is quite a nicely proportioned engine, having just done a Stuart Victoria which has almost the same bore and stroke the Stuart seems quite agricultural in some areas as well as being considerably larger.

I went through the bill of materials last night and priced it up allowing for 300mm lengths of the smaller sections and the bigger bits in the nearest 25mm increments and allowing £25 for a flywheel casting the materials came in at £101.00. Allowing a further £25-30 for fixings etc as they tend to come in packs of 50 that still makes it about 1/3rd the cost of a set of Victoria castings with the added bonus that fabricating and cutting from solid will give you more workshop time for the lower outlay so another win win situation.

If going for the JB Weld option over silver solder then you could actually use cast iron for all the cylinder parts and that would be a bit of a saving over bronze/brass.

Hi Paul, No problem discussing aspects of the design.

Thompstone does not say that the engine is based on any specific prototype, in fact he just presents it as a "Model Horizontal Engine. Since I first saw it I have always pictured it as a small workshop engine rather than anything large so bore would be in the region of 3 to 4 inches which gives a scale of around 1/3rd to 1/4.

1. It's a bit difficult to make out what he is describing in the text (I'll post that later) and the drawing does not help too much. The part I have arrowed in red seems to be shaded as if to represent a curved or rounded surface but there is not outer edge, I would have expected a line down from the end of the cylinder possibly? The way the bottom nuts are visible suggests that whatever support is to the valve chest side of ctr line ? He says that the exhaust has back nuts which make the cylinder fixing rigid so that may be acting as a third leg? I have assumed that the part arrowed blue in the middle is the exhaust going down into the base.

So with those details not being clear I took a bit of artistic licence and used the two round feet which seemed right centred on the bands and just dropped the exhaust down into the base. I'm not keen on the angle brackets that the basic Stuart Victoria uses but it would not be out of keeping to add wider feet in the style of "Princess Royal" or similar which could easily be substituted for my round feet. The Victoria was based on another workshop engine of 5" bore so again quite a small prototype.

2. The decorative cast rings seem quite common when looking at other workshop and generally small engines and there may be even more with them but hidden from view under cladding. If you have a look at these three pages of horizontal engines on Preston's website you can see several examples of one or two bands around the cylinders.

3. Again there are several of the engines on Preston's that have a similar oil or fat pot centrally mounted on the cylinder so reasonable to assume it's not out of place on an engine like this.

4. I'm not sure if there is a specific reason that the split line of the main bearings is angled like this. On an IC engine they tend to be angled the other way which I have always assumed is to better resist the forces during the ignition stroke but as our steam engine is double acting that can't be why. Another thought is that by angling the split line of the bearing it puts the joint above and below the main angles of thrust as the piston moves back and forth which means an uninterrupted oil fil on the surface of the bearing where the load is greater. But I'd welcome any other comments on this one.

It's something you see on most sizes of engine, from the small workshop ones at Preston's, Tangyes used it quite a bit on their various engines not just the popular one that gets modelled but also ones like their "colonial" and right upto some of the larger Corliss engines by various makers.

Edited By JasonB on 14/04/2021 18:43:28

Hi Ron, don't feel you are butting in, the more the merrier.

Yes that is the only practical reason that I can thing of the bands being used to ass strength which may allow the rest of the cylinder side wall to be cast a bit thinner.

Here is the text that went with the GA drawings I posted last week

39A the assembled crosshead and pin with slippers in place

40A Rough cut hot rolled steel for the crosshead guides

40B top guides almost complete, bottoms drilled for the internal corner

41A Milling away material from underside of lower guides

43A milling upper cutout of the lower guide

44A almost complete, just the upper and lower webs to be shaped