It’s been quit some time since I last contributed to the forum and I am still trying to remember how the system works so excuse any mistakes or double ups. The model I am now making is a 1934 Mc Donald tractor in 1/4 scale. It has a single cylinder two stroke diesel engine driving through a 3 forward / 1 reverse gearbox. The “ignition” is by hot bulb and cooling by thermo siphon The chassis is cast and on the model it’s aluminium as are all the other castings. The photographs show various stages of the construction with the front half ( chassis, radiator and fan) now complete. The engine and gearbox patterns have been made and I hope to cast the gearbox soon. I am lucky in that the full size tractor is only 17 kms from my home and so far I have spent 14 hours taking photographs and taking measurement prior to making CAD drawings and patterns. It is an exciting project to be working on and the learning curve never stops!

The full size tractor was made in Australia and the design was based on both the Lanz Bulldog for the engine design and the Rumsely tractor for the gearbox arrangement. The model I am making is based on the 1934 model of which there were 50 full size tractors manufactured. At first the engine pointed to the front but was later turned around so that it pointed towards the driver as this gave a better weight distribution of weight over the rear wheels and improved the steering characteristics. The photographs sent in yesterday shows the pattern for the chassis. The patterns and core boxes are made from MDF and are spray painted with “bog” of the type used on car bodies as this gives a finish that can be drawn on with pencil and gives a small fillet in the corners. I have made a model Lister Diesel engine and will use that experience when designing and making the injection system on this tractor and still keep with in the external shape of the full size tractor. I will show you more details when I reach that stage.

Good Day Roger,

Yes that was my model 6/1 Lister and there is a video of it working on U tube and it was on display at the 2019 MEX. I do have good diagrams of the cam and variable injector system used on the Mc Donald and will try to follow that as much as possible. I have normally made four stroke engines and this is the first two stroke and first with hot bulb and it presents many challenges! The castings shown are some of the largest I have made and push the limits of my equipment and me.

The casting shown above is the result of today’s efforts and was still warm when the photo was taken. It has yet to be cleaned up. The casting is the top cover for the gearbox and the shape can be seen in the photo of the full size tractor. Tomorrow I hope to cast one side of the gearbox as all the patterns and core boxes are now finished. Fingers crossed all goes well!

A

Hi Adrian R2,

The photographs show my rather untidy foundry area of the workshop. The work bench has a sand storage area underneath, casting boxes above and a small cabinet on the left that holds the tools used in the process. The other photo shows the ‘hot’ area where I melt the aluminium using a gas blow torch. The fire bricks generate a vortex around the crucible. The scrap metal on the right is my stock of usable aluminium – Briggs and Stratton crankcase etc. I do use Coveral11 flux to clean the melt and degassing tablets to dive off any gas in the molten metal. I use both oil bound sand (Petrabond) and a local white sand that I mix with a chemical binder/ hardener. Casting is an enjoyable process but it does take time and if you don’t succeed the first time you just try again !

The half of the gearbox ready for assembly and casting and the pattern for the rear axle supports.

9

Today was casting day for the first half of the gearbox and it would have been great to report that all went well but it didn’t . The casting process went well but due to a seniors moment and misjudgment a few holes appeared where they were not wanted! I did say “oh bother” but then realised it was just part of the never ending learning curve. I have now modified both the pattern and core box and will also pack the box more firmly next time for a better surface finish.

The photographs show the out door foundry, the pouring of the aluminium and the casting ( complete with unwanted holes).

The weather conditions here have stopped casting for a while but there is still plenty to work to do in the workshop. The photograph shows a jig that I made up for silver soldering the rings inside the rear wheels. It was well worth the time and effort as I was able to use gravity to help the solder to flow as the wheel can be rotated when being soldered. By making the jig it gave the set up stability and didn’t fall over also I was able to do both sides in one heat.

They

Good Day Adrian,

After all that effort I did consider blocking up the holes by either welding or liquid steel from a tube but decided there was only one way and that was to repeat the process with a modified pattern and core box. The fault was mine ( in the design) and not the actual casting process and all should be OK next time. As we cast outside and the weather was not good it was back in the workshop and I have now made up the rear wheel rims to the point of etch primer.

Fred