A Robinson, in the " Making "

[Alyn Foundry]

The governor is both simple and effective but not very good on an unstable platform. The engine has to be firmly planted to get results. There’s been many an accident on the rally field where they’ve gone out of control due to the engine rocking in opposition to the pendulum.

Morning Jason.

Yes there’s a draft angle but much less than 2 degrees. The new foundry although well versed in “ Greensand “ moulding seem to prefer “ air set “ so you can get away with virtually zero draft.

Cheers Graham.

[Alyn Foundry]

Although some patterns are fairly simple most are pretty complex.

With the aid of some decent wood, a lathe and my trusty Power file the cylinder head pattern is now ready for filleting and paint. A small core print has been made because the inside, where the ignition tube is fixed is angled at around 45 degrees. The second picture is of a burned out head, in fact the full size engine is now on its third one having worked very hard in its day.

By tomorrow I’m hoping to be able to show you the cylinder jacket with its core box. This part will eventually have the honed cylinder liner, a separate component, glued into position.

[Jasonb]

Well at least you should not have a problem replicating that rusty finish

At the rate you are going we should see a running engine by Easter

[Alyn Foundry]

A little sooner than advertised….

The core box started out from two pieces of the same hardwood that made the outer cylinder jacket pattern. These had been thicknessed at my local sawmill. Using 4 wood screws to secure the halves the block was centred up in the 4 jaw chuck. The first operation was to drill right through at 3/4” diameter which matches the smaller core print on the cylinder pattern. The hole was then bored out to suit the open end.

Using an internal screw cutting tool the water jacket space was bored between two pencil marks on the shank. This was deepened by about 3/8” all round.

The final part was to secure two pieces of hardwood to the side of the core box to make the exhaust tract form from the cylinder to cylinder head tract. This is something I have never done before so it will be quite interesting to see how the small core reacts to being almost totally enveloped in molten Iron.

Alan is Beavering away with the bed pattern, hopefully some pictures tomorrow.

 

[Jasonb]

Graham, is there any means to hold the core in position radially so that there is no risk of the exhaust core drooping down and possibly touching the edge of the pattern

[Alyn Foundry]

Morning Jason.

Well spotted….   

Not at this moment there isn’t. To make the core box easier to use I chose to run the tract through the box split line. I’m hoping that the rather fragile core will emerge without the right angled section breaking away during handling.

If folks look closely at the cylinder they’ll notice that the exhaust mounting actually runs from the centre line to the bottom.
This will mean that the core needs to be skewed slightly from its centre line so the end of the tract becomes central to the spigot. Once this angle is ascertained a small section of the cylinder core print will be cut off and glued into the core box to act as a register.

 

[Alyn Foundry]

With the engine being what is known in the Stationary engine movement as a “ headless “ type the cylinder bore can present some real problems regarding boring and honing. Our first model, the Robinson type “ X “ that was built over 30 years ago had the same problem. After a great deal of thought at the time, a separate cylinder liner was used to overcome this problem.

I have obviously incorporated the same method this time around and if you look closely at the core box you’ll see that the water jacket is only brought to the front, shy of the exhaust port. I have also reduced the draft angle to a minimum to facilitate ease of drilling the top and bottom water cooling tracts. The casting can then be bored out to the cylinder liners outside diameter and the finished liner can be glued into position.

As luck would have it the aborted 1/4 scale Hornsby Akryod piston and cylinder liner patterns/core boxes will come in very handy for this model.

 

[Alyn Foundry]

Dydd Dewi Sant Hapus

A bright but chilly start to Saint David’s day today here in North Wales and we do have a couple of Daffodils in bloom.

Due to paint incompatibility some of the patterns had to be re sprayed but we’re back on track. The small Acrylic tube is the core box for the angled ( horizontal ) ignition tube and vaporiser, part of the cylinder head.

 

[Alyn Foundry]

With some help from another pattern maker we’ve finally reached the end of this particular thread. I hope I have been able to perhaps inspire one or two to try this avenue for a new project? Just some minor adjustments and painting before they are sent to the foundry.

With today’s modern equipment in the form of CNC and 3D printing, pattern making couldn’t be easier !

Obviously I’m able to share the fruits with other, like minded engine builders and I shall start a new thread here as the castings become available.

Many thanks to those that contributed, and please don’t hesitate to ask any questions if something is unclear.

   Graham.

[Jasonb]

Well I've enjoyed following along despite some of my opinions on castings  and look forward to seeing what comes out of the sand. Should make a nice companion for anyone who has an X-type and if you can get it to run off the "blowlamp" with it's limited heating that will look the part when running particularly if it can be kept a san oil burner rather than propane.

J

PS don't forget the inlet valve guide.

[Alyn Foundry]

Thanks Jason.

Well, pattern making is really only fabrication in another material isn’t it?   

I have no doubts about the engine running, my first model oil engine was a converted Sphinx. It had a Sparklets soda siphon CO2 bulb stuck in the front end. The problem was with stopping it from revving its  off ! The Akryod was problematical due to scale, I have since discovered that the water cooled injector wasn’t being cooled enough and the oil would vaporise within it.

The Robinson is quite different insofar as the oil sits directly on the valve seat and is partially atomised by the rattle as it enters the combustion chamber. The oil is then further vaporised and ignited by both compression and the hot tube. Luckily it also has the “ hit and miss “ pendulum Governor to keep the RPM in check.

Today saw the arrival of 4 lengths of 1/2” diameter Silver Steel so a couple of crankshafts are in the offing….

   Graham.

Sphinx Oil engine on the left hand side. Circa 1986.

[Jasonb]

I watched the video you posted at the beginning of this thread again just now and the blowlamp looks to have quite a sizable burner by way of diameter so it may be possible to use a modified Sievert or as I mentioned elsewhere one of the "kitchen" type torch burners. If this were mated to a dummy can and the support for the platform that the blowlamp sits on made with a hollow bracket then you could plumb it in to propane but have it look like the blowlamp was doing the work. That is unless you are up for making a miniature paraffin blow lamp

Certainly like the idea of an oil engine as it's something else to cross off the list. I notice the two flywheels on the oil Sphinx no diubt to help carry it over with the higher compression.

[Roger B]

Hot bulb engines typically had quite low compression ratios, around 6-1 depending on the fuel type. Some of the Lanz Bulldog models have overcome the problem of keeping the bulb hot by using a semi concealed automotive diesel glowplug.

[ettingtonliam]

With some help from another pattern maker we’ve finally reached the end of this particular thread. I hope I have been able to perhaps inspire one or two to try this avenue for a new project? Just some minor adjustments and painting before they are sent to the foundry.

With today’s modern equipment in the form of CNC and 3D printing, pattern making couldn’t be easier !

Obviously I’m able to share the fruits with other, like minded engine builders and I shall start a new thread here as the castings become available.

Many thanks to those that contributed, and please don’t hesitate to ask any questions if something is unclear.
 

Lovely! I am a self taught pattern maker, and always enjoyed it, regarding it as just another challenge in the creation of a model or a machine. My pattern making highlights were a 24" planer based on a Tom  Senior No. 3, and the recreation of a Stuart Turner 600 gas engine. The cylinder block incorporated 5 separate cores and I built a wooden model just to show the foundry how it was all supposed to fit together. I believe they used it as a training exercise for one of their apprentice moulders! Mine were all traditional loose wooden patterns, mostly pine, but I did the flywheel (14" dia, 35 lb weight) as a split pattern by building up a sandwich of 12mm MDF and then shaping the curved spokes with a hand held router.

[Jasonb]

I'm sure someone is trying to bring me back from the dark side and convert me to the way of the casting  as I seem to keep finding various boxes on my doorstep packed with bits of cast iron.

This rather weighty one turned up today tipping the scales at 20kg and there is also the beginnings of another project in there too. Flywheel is just over 9" dia for an idea of scale.