Crosskill Demonstration Engine

[Jo]

In one of my many moments of foolishness I did what is commonly known as “opened my big mouth and put my foot in it”  : What I did was volunteered to provide a live turning demonstration on my Cowells Lathe at my model engineering Club’s steam rally this summer. I am already regretting this as it is going to cut into the time available to do important things like buying castings/tools at the show. And will take time out from playing in the workshop as I prepare. 

So my requirements were that I need something to make that could be used to demonstrate different aspects of turning. It shouldn’t cost anything  , should be able to be made from the scrap bin  . So I came up with the idea of making one of these:

Jo

[Bogstandard]

I don't think you will get one of those made in however long the show is on.

Why not make a simple finger or rocker engine instead?


John

[Jo]

No John I do not intend on completing the engine just using it to demonstrate turning.

So I need something that can be made on a face plate. Something to make using a four jaw, a three jaw, between centres and maybe a bit of milling/dividing. 

Jo

[Jo]

The drawings for this engine was left to me as part of a past friend’s estate as was the castings but these were never found  . 

It is still possible to buy these today from Polly Engineering: http://www.pollymodelengineering.co.uk/sections/stationary-engines/anthony-mount-models/crosskills-Oscillating-Engine.asp but as I said it is my intention to make this from scrap  .

Jo

[Jo]

So the problem in part building this engine for demonstration purposes will be three fold:

1.   I am limited by what I can find, beg, borrow or use my feminine charms to acquire (= steal)
2.   I have to try to avoid finishing too much of it when I start enjoying myself.
3.   I have to try to show a range of different machining techniques

The original model engine has less than 21 different parts of which the base, table, flywheel and cylinder are all castings. Mine will not be.

Jo

[Jo]

So how to over come the problem with the lack of castings?

Well the Base is originally a 2” diameter casting that has a basic shape as shown. So my intention is to rough turn something finishing the inner face to 42mm so that it can be mounted on the outside of the three jaw self-centring chuck.

The opportunity at the show can be to improve on the profile around the edge. So a bit of slow turning, maybe with a profile tool or doing a bit of free hand work with a graver

Jo

[Jo]

The table as drawn is rectangular, with a rectangular hole in the middle and four holes one for each of the vertical columns and four for the crankshaft bearings.

As a machining challenge it is no more difficult than machining a valve chest except for the outside which has those thin steps which are going to show up any miss alignment of the cut. My temptation at the moment is to make it from three pieces of steel: two pieces of 1.6mm sheet and a piece of 6mm thick. Brass would be easier on my milling cutters for cutting the hole in the centre but it all depends upon what is in the scrap bin. Much larger than this and I might be tempted to make the thicker section out of four separate pieces and silver solder them together like I did on the S&P Entablature.

The only real opportunity this part offers for demonstration is a bit of facing in a four jaw or milling on the vertical slide…So it is likely to be made prior to the show

Jo

[Jo]

Now the flywheel is where the construction becomes much more interesting…

The original Crosskill engine had curved spokes, the one from this design are straight. So decisions to make. The Flywheel works out to be 76.2mm diameter, 10mm wide it has a thick rim, with tapered spokes and a centre. My intention is to machine this up prior to the show, and maybe use the spokes to show a bit of taper turning. But the main purpose of this part is to show how flywheels can be made up from components.

Jo

[b.lindsey]

Sounds like you are coming up with a good plan Jo.  How long will you be demonstrating...is it like an all day thing or more like a few hours?

Bill

[Jo]

Bill, They are planning to have me providing the "live female turning demonstration" for the full two days. 

I have so far failed to find any volunteers to help me so it could be very tiring

Jo

[b.lindsey]

Oh wow!!  And as you say...leaves precious little time for casting shopping ....bummer!!!

Bill

[Jo]

I am ever hopeful that I will be able to sweet talk someone to help me and I might cheat and wear a skirt  but I already have a backup plan: I hope to be doing this demonstration next to the original designer of this engine and I know he has a soft spot for my Cowells and will be itching to play .

------
Now the really tricky bit the cylinder. Well actually I would argue that turning this up using the casting will be more difficult than making it out of bar stock and silver soldering it together.

I have attached a cross section to give you some idea of the shape that needs to be made. My plan is to make it in three parts the main cylinder which can be made out of a piece of 19mm dia by 29mm brass and two tees that will come out of some more 19mm brass.

I am tempted to mount the cylinder up on the face plate for pretend turning, at 29mm long she is not too much of a handful.

Jo

[Jasonb]

It would be nice if you had a few coloured 3D renderings of the engine blown up to say A3 which would enable the punters to see what goes where, maybe even an exploaded view though a transparent rendering is just as good.

I think if you get a few of the basic fabrications made proir to the show then you can just give them a clean up and bring to size live.

I'm not going to have as much time as I thought that weekend unless I can get someone to let the dog out, besides someone will need to accompany you on your travels around the show site to keep your buying habbit in check.

Have you been risk assessed yet? 

J

[Jo]

The remainder of the engine is made from bar stock on the original engine so they should be simpler:

Columns: These are tapered columns with square ends. Now you can seek to make these out of 6.35mm square or make them out of bar and add square washers. Either case they provide a means of demonstrating between centre taper turning.

Cylinder covers: These are 19mm diameter and provide an opportunity to demonstrate use of a thin piece chuck…If I make one.

The remaining parts will need to be made prior to the show and taken along. Leaving me with the opportunity to knock up a bunch of fasteners, including some studs which will demonstrate use of tailstock die holders.

So it must be time to start putting her together:

Jo

[Jo]

It would be nice if you had a few coloured 3D renderings of the engine blown up to say A3 which would enable the punters to see what goes where, maybe even an exploaded view though a transparent rendering is just as good.

I think if you get a few of the basic fabrications made prior to the show then you can just give them a clean up and bring to size live.

I'm not going to have as much time as I thought that weekend unless I can get someone to let the dog out, besides someone will need to accompany you on your travels around the show site to keep your buying habit in check.

Have you been risk assessed yet? 

J

I might draw up some 3D renderings and drop them on an AO sheet to make up a poster. I was already considering making up a couple of posters showing various machining processes of parts from some of my engines a single AO color poster of governor making might be nice 

Yes a bit of prep followed by minor turning. I suspect that once Model Engineers start gassing nothing will get done  .

Risks/opportunities, I see two main ones:


1, Someone might offer me castings  . (I will be selling the spare S&P casting set)
2, I might get chatted up by a handsome fella but knowing my luck it will be by some dirty old man.


As for their idea of health and safety requirements.... don't get me started.  Too much hassle and this will be a once in a lifetime performance. 

Jo