Here is a list of all the postings Four stroke Fred has made in our forums. Click on a thread name to jump to the thread.
|Thread: Mc Donald Model tractor|
While every thing is ready for a casting session the weather has postponed any progress for some time as last night we had 200mm of rain. In the last week we have had 325mm and every thing is very soggy!
This week I have made and machined the three castings for the air intake system.The photographs show the core box, pattern and core, and then two views of the completed reed valve air filter system. The other night we had 120 mm of rain in 12 hours together with thunder and lightening but fortunately it has cleared away out to sea and this means the 3D printer is now back in action printing the the revised core box for the crank case. Each of the four parts takes about 14 hours and by the end of today I will have printed part one! It looks as though I will be ready to cast the crankcase again next week ,weather permitting. T
No this is not a pot belly heating stove but the air filter and intake pipe for the tractor. I have yet to make the casting that connects it to the back of the engine and reed intake block. The top and bottom are aluminium castings and the side is rolled steel sheet. I have decided to make a new crankcase casting as there are areas “ in need of improvement “! I am in the process of a redesign of the internal core and that means more 3D printing and I have to work that in with the weather as we are in storm season and I do not want any equipment damaged by lighten strikes or stop half way through a 15 hr pint! While the printer is busy I will be designing other small parts and reading about hot bulb engines. There is always plenty to think about and do.
Today has proved that the engine casting can be machined with the equipment I have in the workshop but it took a long time to work out if it could actually be done. The problem is two fold, one is that its quite a large lump of material to work with and secondly it’s a rather awkward shape to hold and centre on the lathe. It does look rather precarious that far out from the head stock but it is clamped by a long bolt through the crankcase and a clamp across the top. The speed was kept low and the boring process was just that! Each pass took ages but I couldn’t risk a higher speed. I will be making another casting as there are parts that I feel need to be changed or checked. The school report would say” 7/10 can do better”. The main problem is the centring of the core as on this example it had dropped a few mm off the centre line, also part of the water passage needs to be rotated 30 degrees so that the head bolts have material for the studs to be fitted and the injector has an unobstructed position in the head. The second problem is easy to solve as I just have to glue the two halves the correct way as they were designed! This casting will not be wasted as it can be the basis of another model but not on this tractor.Yes, today was a big learning curve and it will make next time easier as I now know it can be done and how to do it, just put it down to the acquisition of yet more experience!
As can be seen in the photographs I have had a good day machining the casting that I made yesterday. The top photo shows the injector base block being machined flat. The second shows milling the exhaust port and the last shows the boring out the crankcase and creating a datum base to work from. Looking forward to more of the same tomorrow and it’s a change from playing sand castles!
Thank you to all those who sent comments and I am pleased you enjoy following the path of the construction of this model. With regards to the weight of the pour - 4.35 Kg of metal was used in the pour of the casting and when the runners and risers were removed the weight was 3.10 Kg ( with most of the core sand removed). I do still have to remove the some sand from the water passage and that is one of the tasks for today. We had sufficient metal left in the pot to pour the spare into a couple of tin cans later to be machined into solid rods of aluminium.I am also considering casting another spare unit while I have all the casting gear set up - a glutton for punishment! This will not happen for a few weeks as I will check that the mark one is OK as I don’t want to repeat any mistakes if they have occurred in the mk1 edition.
After months of work the day to cast finally arrived and even the sun was shining. I had to transport the two half flasks to my mates place in the car and the journey was taken very steadily to avoid any bits falling into the mould. On arrival the the two parts of the boxes were assembled to form one unit and made ready for the pour. With metal ( we used faulty new Diesel engine pistons) it was then poured into the mould.. I had one runner and three risers except during the pour the risers became runners and the runner became the riser due to the metal flooding the top of the flask! Oh bother - the chances of a good casting did not look good! On returning home to my workshop the flask was opened but expectations were not great. The sand was removed and the casting gradually revealed- oh what a joy to behold. There it was with no visible faults as shown in the photo with runners and risers attached and then with them removed and almost ready for machining. The other photo shows the pouring action. It will be good to start the machining but working out how to hold it is another problem. A big thanks to John,John, and Ray who helped out.
These are the 3D prints of parts of the air intake system showing the housing for the reed valve in the centre, the support for the air intake manifold on the right and the reed valves on the left. All the green parts will be made in aluminium and bolted to the crankcase of the engine. The reed valves where donated to me by our local motorcycle dealer after he had made a visit to the workshop and viewed the progress on the tractor. As the lager castings are poured outside we will have to wait for the weather to clear up before the crankcase can be cast but hopefully some time next week. This last week has seen hail 160mm in dia fall at Mackay, north of us - the storm season has arrived with vengeance !
Today I made the boxes for casting and then did a trial run to check to see if all the parts would fit together. The patterns came out quite well but there were a couple of places where there was a slight overhang (that I had omitted to see) and the sand pulled out. Modifications to both the pattern and by making small changes to the core box should over come these faults. I will repack the boxes and then cut the runners where the metal flows in and risers that allow gasses to escape and act as a reserve of metal when the casting cools and shrinks.
After many attempts and a big learning curve success has arrived at last! After the modifying, painting and polishing of the core boxes I packed them with sand mixed with sodium silicate. The packing is not easy as it has to carried out in a certain order but at least with the CO2 method it gives me time before it is placed in the plastic bag to be gassed. After experimenting I discovered that half a kg of sand and two table spoons of sodium silicate seem to work well. There are sections of this core that are quite thin and also as the sand is fine it does need a strong mix to bind it all together. As the saying goes “ Small things make perfection but perfection is no small thing”. These cores may not be perfect but I am quite pleased with the results so far. The two halves will be glued together and then placed over the main engine core to create the water passage of this engine. The photographs show the two halves and then the dry assembly.
Development continues with the core for the water passage. I have tried to make this core using the resin sand but due to the complicated nature of the beast time runs out and the mixture hardens before I have a chance of finishing the packing. I am now trying the CO2 process as this gives me more time. The picture shows the packed core box, the plastic bag in which the core box is placed and then the CO2 is added in the form of the Sparklet cylinder and jig. The whole unit is then sealed up and the bag inflates with the CO2 and it is left to harden up. The first time I did this I hadn’t made the mixture strong enough and parts crumbled and so the experiments continue with the hope that I will succeed in the end. The changes in the colour of 3D printed core Cox is a result of continued modifications.
This is the first half of the revised core and box for the water chamber and shows the castellated top. This leaves space for the water and the parts in between are for the cylinder head stud location. This was the easier half to make and the challenge is now to make the second half with all the ports spaces and supports.
This is the core core box in its present form.
This picture shows the results of some experimentation with the core for the water passage and proves that not every experiment is a success as the sand was not packed into the castellated sections tight enough Packing the core box in its present form proves a problem and a rethink is required to make sure the sand can be packed into all the recessed parts. This core has to fit over the core in the background and makes the space for the water to circulate around the cylinder. I may opt to make the core as two seperate pieces and glue them together but this will entail more 3D printing. While the printer is doing it job it gives me time to continue the design work on the injector pump and also the clutch unit - not much to show but work that has to be done.
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