Mc Donald Model tractor

[Adrian R2Participant @adrianr2]

That tank looks really tidy. What is it with old tractor designs and things passing through tanks? On the B250/B275 International Harvester co decided that it was fine to do the same with the steering column.

One magic wand I saw recently was a 3d printer for making sand moulds – not hobbyist stuff but a fascinating way to turn designs into metal.

[Four stroke FredParticipant @fourstrokefred]

Thanks for the comments Adrian and yes I do have a 3D printer and do use it to make patters and find it very useful. The larger patterns and core boxes are made from MDF and this week I hope to start on the core box for the inside of the engine.

Fred.

[Adrian R2Participant @adrianr2]

The 3D sand printing process I mentioned creates the moulds and cores directly from the CAD model, so no need for patterns at all, and you can cast pretty much anything in one piece. Defintely magic wand territory if you can just print one out and pour metal into it.

[Four stroke FredParticipant @fourstrokefred]

As part of the evolving design of this tractor engine I have revised the sand cores for the inside of the engine. It’s OK to design the shape but then it has to be made so that it will fit together for casting. This is quite a complex unit as there is the main central core , a transfer port, exhaust port and the water chamber cores that are all seperate parts and have to be able to be fitted together. The castellated top to the water core is to allow the cylinder head to be bolted on and for the core to be supported in the casting flask. There are many problems to solve and just when you think you have mastered it another pops up! It is now reaching the stage where I will soon be able to start to make the various core boxes- fingers crossed that they all work. It would have been good to have had a 3D printer that will print with a sand/ resin or some other magic mix but I will have to win the lottery before that happens! The photo shows the half main crankcase core, inlet port and water chamber.

Fred.

[Four stroke FredParticipant @fourstrokefred]

This week has been spent thinking and drawing the various patterns and core boxes again. Today I made another visit to the full-size tractor to check on some of the critical dimensions and have now clocked up 24 hours on this part of the task. Trying to re measure the position of the exhaust port was a messy business due to an abundance of oily deposits! I have decided to remake the crankcase/ cylinder pattern as to remove it from the chemically bonded sand would have proven a problem. I am thinking that I will “ quarter” the pattern and make special boxes but more of this later. I hope to be back in the workshop actually making bits tomorrow.

Fred.

[Henry BrownParticipant @henrybrown95529]

Well worth all the effort though Fred! Just a thought – is it worth doing a scaled down print of the cores just to se how they look?

[Four stroke FredParticipant @fourstrokefred]

Good Day Henry,

Last night I thought the problem over and I will now 3D print the pattern / core box and yes it would be a good idea to make them on a smaller scale just to check that all is well. I have just bought a larger 3D printer with a print area 4x the size of my other machine but have a few problems with the soft ware which is a pity as I am eager to have it up and running!

Fred.

[Jon LawesParticipant @jonlawes51698]

Forgive me for saying it but this is just the sort of thing I love to read about in the Model Engineer magazine. The quality of the workmanship and the writeup would make for a fantastic series.

[Four stroke FredParticipant @fourstrokefred]

Good Day Jon,

Thanks for your comment and yes I will consider an article for the M.E. based on the above script and photographs but will probably not include a full set of drawings. This column is not so much about making the model as the whole process and thinking behind it. When I did the article/ drawings on the Saunderson and Mills tractor it took a great deal of preparation time and as you get older time is precious! For me working on a project such as this tractor is a challenge and it’s more about the journey than reaching a target. Delving into the unknown ( for me) just adds to the challenge and excitement – there is no guarantee that the engine will work but that doesn’t stop progress and if it does work Yippee !

Fred.

[Four stroke FredParticipant @fourstrokefred]

Good idea Jon.

A quick quarter scale 3D print of the lower half pattern – should work when made as a full size pattern.

Fred

[Four stroke FredParticipant @fourstrokefred]

Engine development continues. The photo shows 2 of the half size patterns for the lower half of the engine and are being used to check out any problems before printing the full size patterns thus saving both time and materials. I will test them in the chemically bound sand to see what happens! When I have finished with the full set of this small size of pattern I will glue them together, add more details, paint and mount it on a stand and present it to the farmer in appreciation of the access to the full size tractor. The not such good news is that I have had to return my new 3D printer and have had to resort to my faithful smaller “ Up + 2 “printer and glue parts together. The new printer has a work area x4 the size of the small one but the old one has not missed a beat in all the years I have owned it. In the next few days I will print the top half of the above small patterns and play in the sand!

Fred.

[Adrian R2Participant @adrianr2]

Hi Fred – Just wondering whether you'd attempted this yet and if so how it turned out?

[Four stroke FredParticipant @fourstrokefred]

Good Day Adrian and fellow model engineers,

There has been some delay in producing 3D prints for both core boxes and patterns as I had to return my new printer as it had a fault with the other board. The good news is that I am expecting it to be returned today. I have made the wooden pattern and core box for the piston and hope to cast this item this week. The connecting rod and internal flywheels have been laser cut and are waiting to be machined. I have also bought all the bearings and oil seals as these were needed for the design stage of the operation. I will post more photographs on the progress soon.

Fred.

[Four stroke FredParticipant @fourstrokefred]

Today I cast the piston as shown in the photo using a resin for the core sand and Petrabond sand for the flask. The 3D printer was returned but with out the power lead and instruction book! Tomorrow’s task is to set up the printer and also machine the piston and fit the rings. I can see that casting the cylinder/ crankcase is going to be difficult and expect that not all the attempts will be successful. Each attempt will be part of the continuing learning curve.

Fred.

[Howard LewisParticipant @howardlewis46836]

The man who said "The devil is in the detail" was not wrong.

But the care that you are taking will be repaid with success later on.

It will be a model worth travelling to see in motion.

But across the world, sadly, is too far for me.

But keep up the splendid work, it is a fascinating account.

Howardi

[Four stroke FredParticipant @fourstrokefred]

Good Day Howard,

Thank you for your comments and I am pleased to hear that you enjoy my efforts in the shed. On my visits to the UK (MEX) one thing that I have managed to learn from the “ greats of model engineering” is that you continually strive to do your best with the experience, ability and the equipment that you have. I hope my efforts inspire others to take up the hobby at a level they are comfortable with, remembering that we all have to start some where.

I now have a working 3D printer and over the weekend hope to print some of the major patterns for the engine. Today I cast 3 pistons but had to reject one as it had a flaw caused by using too much resin in the mix. This created a gas bubble inside the piston and rendered it u.s. Tomorrow I will machine one of the castings and fit the gudgeon pin and piston rings.

Fred.

[Four stroke FredParticipant @fourstrokefred]

P.S.

I forgot to add that the Saunderson and Mills made it to the 2019 MEX perhaps at some time in the future depending on COVID the Mc Donald may make a similar journey if the MEX is still around ( I hope it is).

Fred.

[Howard LewisParticipant @howardlewis46836]

Fred,

It will be an awe inspiring exhibit when it comes.!

Do let us know when that will come about.

Howard

[Four stroke FredParticipant @fourstrokefred]

This is engine part number one. The piston is a flat topped deflector ( if there is such a thing) with the two cutouts being the deflectors for the gasses. Although I have the laser cut connecting rod I am going to try casting one in aluminium in order to reduce the weight factor. I am also giving some thought to the reed valve induction set up. I do have a an old Frog 149 cc model diesel engine with what was called “vibramatic” induction and will have a good look at that for ideas.

Fred.

[Roger BParticipant @rogerb61624]

I'm still following and enjoying

I decided to reduce the doubt for my two stroke diesel by using a commercial reed valve from a moped/scooter. This was not expensive however if you have a dealer/workshop near you you could see the various sizes and shapes available.

[Four stroke FredParticipant @fourstrokefred]

Good Day Roger,

Thanks for the email. I did visit my local motorcycle shop and after explaining what I was after and what it would be used for they donated me a set of small Boyesen reed valves. What capacity is your engine? The tractor engine will be 79.5cc and hopefully the revs will be quite low as it has a heavy flywheel to carry the moment through.

Fred

[Roger BParticipant @rogerb61624]

My engine is only 20cc so those valves are a bit big but that will hopefully help the volumetric efficiency.

[Four stroke FredParticipant @fourstrokefred]

This is the cast aluminium connecting rod and the piston. I recycled an old Briggs and Stratton con rod and hopefully by not over heating it in the crucible I may have retained the metals characteristics. The big end bearing is a needle roller running on a hardened and ground sleeve and the small end also uses a needle roller but it runs on a heat treated silver steel gudgeon pin. The pattern for the crankcase /cylinder is in 8 parts and when made will be glued together to form 4 quarters. Each of the 8 parts will take 6+ hours to print on the 3D printer but that’s next weeks project.

Fred.

[Four stroke FredParticipant @fourstrokefred]

[Four stroke FredParticipant @fourstrokefred]

This is the result of 50+ hours of 3D printing in PLA. The 8 parts are held temporarily held together with dowel pins, hence the gaps. Each quarter will be tested in oil pound sand before parts are glued together. If all is well then chemical sand will be used to make “ bricks” that can be later glued together ready for the casting process. I still have to finalise the core shape as this does present a real problem in both the making/ assembly and the casting. I may even have to end up with a half wet half dry liner – more thinking required !

Fred.

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