A Robinson in the making. The conclusion.

[Alyn Foundry]

Rather than mess with my last post having realised there should have been some extra content….

The most important thing I failed to mention was the accuracy of the finished components. If the mould is made to size then the cold casting will end up being just fractionally smaller than the original dimension. This means that minimal extra machining is involved. Zinc alloy has quite a low melting temperature and I would seriously recommend that the more enterprising members give it a try. Here’s a short video of making a bearing for our Gardner gas engine.

<a href="https://www.youtube.com/watch?v=tXp8hEamWtY" target="_blank">http://www.youtube.com/watch?v=tXp8hEamWtY</a>

The broken glass used to seal the mould bottom came from our multi fuel stove window.

  Graham.

[Alyn Foundry]

A short one today.

Exhaust valve chest.

This will take little to describe and just a bit longer to machine. A solid Iron casting with the correct shape is placed into the 4 jaw chuck. It is then centred up to itself. A quick face off before drilling and reaming to 0.125” for the exhaust valve. I used to have home made tools to form the exhaust tract but I have recently discovered the cutters used for magnetic drills. These cut a neat hole but leave a central core which makes for a great valve guide. All that’s required to finish the job is cut back the guide a bit and cut the valve seat.

The casting is removed from the lathe chuck and transferred over to the pillar drill for the exhaust outlet hole. In this case drilled and tapped to 1/4” BSP. The two by 2 BA clearance holes will be drilled later when the chest is correctly mated to the cylinder casting.

I told you it wouldn’t take long….

[Jasonb]

Working drawings, whatever next

[Alyn Foundry]

Working drawings, whatever next

Definitely not as good as yours Jason but Mathew got the picture.   

[Alyn Foundry]

Cylinder head.

Another simple casting, mainly solid with a small cored cavity at the front for the ignition tube and vaporiser.

After the usual fettling of flash etc I needed to use my smaller 4 jaw chuck to handle this casting. I had already flatted off the top flange previously in the milling machine. Initially I bored a 19 mm hole half way and then dropped down to 7.5 mm for the ignition tube thread. The front face was cleaned up and brought to the correct thickness. I also machined its edge. The casting was then turned through 90 degrees to bore out the inlet valve cavity. The casting was then moved over to the pillar drill for the inlet cavity connection hole. At this point I hadn’t made the inlet valve chest so the cylinder head was then put on the rotary table and the 3 by 2 BA clearance holes drilled for its mounting to the cylinder.

Once the inlet valve chest had been machined it was temporarily glued to the top flange and the 2 BA tapping holes drilled as a pair. There’s not much more to this component other than tapping for the valve chest studs and an
8 x 0.75 thread for the stainless Steel ignition tube. The hardest bit was the small opening at the front for where the lamp burns. Even Carbide wouldn’t touch it!

As an additional note, the combustion space ended up being opened up to 30 mm as the compression pressure was too high initially.
 
First picture. Original, burnt out cylinder head.
Second picture. Loosely fitted to the cylinder.
   Graham.

[Alyn Foundry]

Inlet valve chest.

Just an elongated flange really. However there’s a little more to it than that.

History first. The patent granted to Horace Robinson shows a valve with a double seating. The arrangement caused the liquid fuel to fracture into smaller droplets aiding vaporisation. This arrangement was considered but I decided upon using the same valve as that fitted to my Robinson X type replica. This is a simple “ flat “ valve closing off six holes from the outside. Five of the holes admit air and the sixth has the fuel metering control valve fitted. The flat valve always rattles when opening so I figured this would be enough for the model. My guess turned out to be successful so I’m running with it. This valve works very well with the Paraffin fuel but with gas there’s always a little leakage.

There’s not much to explain about the machining side, once trued up in the 4 jaw chuck it was just a matter of drilling and reaming the 1/8” hole for the valve stem. Then cleaning the front face for the valve to seat against. A little tip, don’t forget to relieve the central hole as you always get a chamfer between stem and valve. The casting was then offered up to the rotary table to drill the six holes for air and fuel. The valve was hacked out of some mild Steel bar and then the finished article put on the bandsaw to separate it from the stock. I’ve tried to part things off in the past but usually disaster strikes and the whole exercise ends up in the bin. Better to be safe than sorry these days.

The most tedious part is “ grinding in “ because trying to rush things with power usually puts scores in the metal that are a real pain in the proverbial to remove. Just good old fashioned elbow grease and patience gets the job done. I have a small tin of fine Carborundum power that will last the family several generations.

For testing the engine I used a steam blow off valve for the fuel control but I might have to rethink this as it gets too hot to touch after a few minutes.

The first two pictures are excerpts from H Robinson’s patent application.

The other two are fairly self explanatory. Including the senior moment with the indexing! 

   Graham.

[Admiral_dk]

The other two are fairly self explanatory. Including the senior moment with the indexing! 

When we are young - the excuse (explanation) is usually down to lack of Experience ....
And when we get too  to use that one - it's called a 'Senior Moment' .... 
... and I have completely lost track on both accounts 

Per

[Alyn Foundry]

Have I forgotten anything?

I’m sure you’ll let me know. Please feel free to ask questions.

As with all my previous builds the engine is assembled bit by bit. The conrod length was found by inserting the piston into the bore just touching the end and then relieving it. This turned out to be way too much compression so a second rod was made to leave 13 mm space. In all cases the fitting of parts is found by offering one up against the next. I then leave it up to the draughtsman to finalise the measurements. Unlike some engines the Robinson is fairly simple in construction and a testament to its inventor.

As stated previously the first run saw the engine trying to fire at around 120 degrees before TDC. Only by the use of a power drill was it able to run. A call to the museum saw the cylinder head being removed to find that the combustion space happened to be 1500.00” not 0.010” like I had got! Hence the shortening of the conrod. The second thing that became apparent was the connection between cylinder and head was also larger than imagined. More remedial work was required, also mentioned earlier.

The next test run was amazing, I could use a single pull on the flywheel and away she went.

So I’m now at a point where the model is a good runner leaving me with the rather fiddly bits left to do. The governor….

At this time I literally have no idea whether this is going to work using liquid fuel. With gas I don’t see a problem but the liquid fuel will keep dripping into the valve seat and we could end up flooding during the “ miss “ cycles. Only time will tell.

Another problem to solve is the permanent lamp. It would be really neat to have a fully functional Paraffin blowlamp but I fear the scale might be a little too small. I’m toying with the idea of a small Paraffin wick lamp but instead of Glass a metal chimney to pull sufficient air to create a clean combustion ( Blue flame ) just like the Aladdin mantle over wick lamps. The exhaust would then be funnelled directly under the ignition tube.

As I close this chapter I would like to thank Jason Ballamy for his help with some of the more complicated patterns and look forward to seeing his Robinson HA engine emerge from his workshop.

Pictures of the  “ pendulum “ governor assembly as fitted to the original engine.

   Graham.

[Admiral_dk]

Great result and an interesting story     

If you really desire a mini blow torch - have a look at Find Hansen and his miniature diesels and semidiesels - the later have mini blow torches. As others have found out - he is not really showing much more than what you can see in his YouTube Videos.

Per

[Jasonb]

That 1/4 scale Pool oil engine that was posted today on FB had quite a dinky blowlamp

[Alyn Foundry]

Yes, I’m guessing at Spirit fuelled rather than Paraffin.