Muncaster 2 Cylinder Engine

I've done a plot using those sizes I got off the scan, it's close but does drift off to one side, changing the right link for Jules' length makes it a lot worse but he may have tweaked the mounting points.

Also tried substituting some nominal imperial sizes based on the horizontal link being 3" but get various deviation from the piston tod axis.

Some more fiddling ha sgot me the required stroke if I allow a +/- limit of 0.15mm on the piston rod in it's hole so I'm sure it could be made better with some more playing about.

However I have just found this which looks promising, I think Michael may enjoy a look. part of this source of interesting stuff

Thanks, Jason, for the links to linkages

I’ve only just arrived home, so that’s my evening entertainment sorted.

MichaelG.

Another useful reference: **LINK**

https://www.gutenberg.org/files/27106/27106-h/27106-h.htm

Consider Figure 14 in the second section

[sorry, I haven’t found the William Freemantle patent]

Now … Here is the Scott Russell mechanism, 21st Century version: **LINK**

https://jaset.pressbooks.com/chapter/design-and-analysis-of-a-modified-scott-russell-straight-line-mechanism-for-a-robot-end-effector/

MichaelG.

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Edit. __ Appendix E of this PhD thesis is also worth a look: 

https://core.ac.uk/download/pdf/186333083.pdf

Edited By Michael Gilligan on 25/10/2022 21:45:43

Edited By Michael Gilligan on 25/10/2022 21:47:31

After a bit of searching on the net, I am a little wiser. The Watts linkage and Peaucelliar -Lipkin linkage has 6 levers to accurately aligns and supports the piston rod with the cylinder axis. **LINK**

The Muncaster engine has a simpler system, although not perfect, should work for my model engine. This is the result of my investigation so far. I have plotted the offset of the linkage arms in relation the axis of the cylinder and found that the slot in the left arm only needs to be 0.5mm long to compensate for the difference in length as the arms rotate.

When the piston rod is fully down , the rod end is guided by the cylinder bush and cannot move sideways. The length D=26.5mm. When the crank is at 90 degrees, D=27.0mm. At 180 degrees D=26.5mm but the rod end can move to the left because of the 0.5mm slot in linkage arm .

My thoughts are that If I lengthen the vertical (113mm) link on the left side slightly, I can get plus/minus 0.25mm offset at the top position.

It’s a tad much to take in without drawing it myself - but did you allow for hinging at the bottom of the 113 rod in your work?

pgk

Beautifully illustrated, and tabulated, Paul

But, [along with pgk, I presume] I am concerned by the 113mm dimension on the left

113 defines position of that link when it is vertical, but I can see nothing to describe the distance between its pivots.

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Please correct me if I am ‘barking up the wrong tree’

MichaelG.

And the rod is not 113mm long, thats the height above base

Please forgive me if I am being delusional, but I think I may have sussed the underlying problem here

In this model, the block on the right-hand pillar appears to be used simply as a bracket and pivot point for the duplicated arms [E]

In the classic Scott Russell mechanism, however, it provides for a sliding motion:

**LINK** [as provided earlier]

Ref. https://jaset.pressbooks.com/chapter/design-and-analysis-of-a-modified-scott-russell-straight-line-mechanism-for-a-robot-end-effector/
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So; the model is avoiding that fundamental complication by enlarging another pivot into a slot

Thus missing the basic concept of the mechanism

[ rather like putting a dummy governor on a model engine ? ]

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MichaelG.

Waiting to be shot-down in flames

Hi pgk, The CAD model is fully constrained and pivots as it would in a real model.

Michael, It is a different type of mechanism and also simpler than the one I put in the link above. No sliding surfaces are used to guide the piston rod, just linkage arms. (not as good as trunk guides as used on other engines)

The flywheel in the 3D model can be rotated and set at any angle (shown below at 0, 90 and 180 deg,) which moves all of the associated parts which can be dimensioned in a 2D drawing.

I tried raising the vertical link slightly to see if this improved the offset at the top pivot but was not successful. Now will try varying the lengths of the other arms to see what happens.

Edited By Paul Lousick on 26/10/2022 10:38:42

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Sorry, Paul … I think we might be at slightly crossed purposes

What I was trying to say was that I think either Muncaster’s original, or the subsequent CAD interpretation, gives the appearance of being a Scott Russell mechanism, but isn’t actually.

MichaelG.

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Edit: __ As quoted on p1 of this thread:

[quote] unique for that time, these were designed as models, not scaled down industrial items. As such they were designed in their own scale [/quote]

Edited By Michael Gilligan on 26/10/2022 10:52:57

Michael although the Russel is a bit different you are indeed right that the slot will allow sideways movement so it's not a "straight line" one on the model which is why Paul queried it in his opening post.

Julius has been know to do similar what a model locks up during a simulation, as I have said it makes it "work" on the 'puter but I'm not aware of a CAD program that simulates the knocking and wear that may result.

I asked about the linkage over on MEM forum and although no one has come up with a perfect solution yet, this recent reply uses software to plot the path of the big end from this simulation,

This is the plot for those that can't see it on MEM

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Busy afternoon, so I’ve only just seen your post, Jason

At the risk of repeating myself …

Yes, I agree Paul’s opening query was perfectly reasonable.

[in the context of Muncaster’s design for a model] Paul asked:

”Does anyone have geometric design data of how these linkages are supposed to work?”

The answer to that must, I fear, be No … because they are not supposed to work [!] and therefore there is no requirement for geometric design data.

… they are simply a visual approximation of something which would work if the model was fully and accurately detailed.

MichaelG.

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With my emboldening for emphasis +1

I would really like to see how Muncaster detailed that pivot

Fixed or Sliding ? … that is the Question

[ and I suspect the answer might be: He didn’t ]

MichaelG.

Alternatively … Does anyone know for sure whether the “little book” is a straight facsimile of Muncaster’s articles in Model Engineer ?

**LINK**

https://www.chronos.ltd.uk/product/model-stationary-engines-their-design-and-construction-by-h-muncaster/

… if so, it might be worth £5.50 just to satisfy my curiosity.

MichaelG.

This is a link to Edward T Westbury's post about the Muncaster engines which were in Model Engineer.

The 2 cylinder is listed but does does not contain the complete article which was in a later issue of ME. Does anyone have a copy ?

**LINK**

I’ve just found an archived advert for a 1913 edition of Muncaster’s book

**LINK**

https://www.peninsula-live-steam-engines-tools-and-supplies.com/ourshop/prod_6977728-RARE-1913-EDITION-Model-Stationary-Engines-Design-and-Construction-Muncaster.html

Doesn’t really get us any further, but I would guess the images are better than the Tee Publishing reprint.

MichaelG.

Digging around in the vague recesses of my mind, I recalled I might have bought a copy of that reprint once. So digging around in the vague recesses of my library, I found it!

It is worth GBP 5.50 and the reproduction quality is good. But there is no mention or drawings of the parallel motion linkage, pseudo, real or otherwise. There are drawings in it of a single cylinder entablature engine of very similar appearance but it uses the more conventional cross-head with vertical square guide bars running between the top of the cylinder and the bottom of the overhead table.

The other drawings/articles in the book are for the more usual mix of double cylinder marine engine, horizontal mill engine, and vertical engines, all more the type of thing we see from Stuart Models etc. Includes nice drawings and words on making a ball governor and the connected throttling valve. Ditto reversing gear.

It was first published in 1912.

The words are rather sparse with not a lot of "how to" full words and music. The instructions for the entablature engine are one long paragraph, probably about 200 words, with one GA drawing with most of the dimensions left to the initiative of the resourceful builder.  But I have no idea if that is how ME would have published things in that era or if their articles would have been more in depth.

Edited By Hopper on 27/10/2022 00:34:59

Thanks, Hopper … glad to hear it’s a good reprint, but disappointed by the absence of info about the linkage.

MichaelG.