Casting Process Advice

Ian@StEnochs

Western Thunderer
What sort of RPM are you spinning at and do you happen to have a photo of the turntable motor arrangement under the tin please (good choice of tin BTW;))

Hi,

I tried to take a photo today but as the motor is tucked under the alsorts tin it is not possible without dismantling the whole machine. However I can tell you that it is a Canon motor driving through a Ron Chaplin 30-1 reduction gearbox. The inline one originally sold for using in JLTRT diesel bogies. As you can see from the photo I use a very basic power controler which came with one of my sons train sets and only has 3 speed settings. I usually run at the middle speed unless there are some thin sections which need a bit more force to get the metal in.

Happy modelling.

Ian!
 

Ian@StEnochs

Western Thunderer
Hi All, Casting again! This time buffer stocks.

On my latest loco build I need some buffers and I have used up all my stock. However as I model one of the less popular railways there are no commercial buffers available so as I want them correct I need to make my own. As described previously on this thread I do a bit of white metal casting on a home made machine. However for buffers the results are not always good enough. The trouble with a two part disc mould is that the parts have a part line and because of the pressure keeping the mould together the resultant castings are not always round. One thing I do not like doing is fettling castings to remove the flash which, if there are bolt heads, can end up with less than acceptable components.

To get over this I gravity cast the buffer stocks. This is how I did it. Firstly a pattern. Worth spending time on and adding details like proper hex headed nuts. I turned my pattern in brass, drilled it for bolt heads on a rotary table to get the correct spacing and soldered in Scale Hardwear nuts. As I intended machining the spigot after casting I did not drill through the body but just made a start for the drill. The pattern is shown below on the left screwed into a piece of plastic tube.

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The pattern was then fixed into the plastic box, one side removed, with some plasticine modelling clay. The pattern was embedded right up to the base and the surface marked with a couple of indents for register. After a quick spray with mould release spray the box was filled up with Tiranti RTV rubber. I mix the rubber and hardener in a yogurt pot, remove some of the air in a bowl with a lid and a hole for the workshop vacuum cleaner hose to fit and suck out the air. When filling the mould it is worth taking it slowly and to do a degass in the bowl before filling completely.

After leaving overnight the plasticine is removed and the other end of the mould filled.

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Next day remove the pattern and cast! I dust the two mould parts with talc using a soft paint brush, fit them together and pour molten white metal from a little ladle heated over the gas ring. A bit of common sense and care is needed, wear eye protection, work on a tray to catch any spillage and make sure the other half is out!

I use mostly scrap white metal and only heat it hot enough to fill the mould, a wee bit of experience will tell you when to pour, any slag on the top is easily lifted off with a bit of bent brass strip. Also make sure you only fill the mould and do not over fill or you will trap the cast in. Been there! To help the metal fill the bolt heads I usually dunt the mould a couple of times before the metal goes hard.

The photo above shows the two parts separated, the one on the left us how you want it, that on the right shows what happens if you don't keep the two mould parts tight together, flash. I put both in the plastic frame with an elastic band to hold them tight.

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Next job is drilling the stock. I use my lathe but I tried it on the pillar drill and it works ok but not as easily. Two holes, one for the buffer spindle and a smaller one for the shank.

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The next job is to turn up a mandrel to hold the body while the spigot is turned, just a bit of brass rod held in the chuck and turned a push fit for the body.

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Here you see the buffer body pushed onto the mandrel and the bottom faced off and a spigot turned. I use a knife tool with about 15 degrees top rake on white metal and turn at 600 revs. You will see that the buffer is cast with the wooden pad on the buffer base which was not used on every loco. I chose to include it as it is easier to turn off the extra if needed than add an other bit.

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And here is the finished buffer along with some more bodies. The two casts on the right show a good one and one with flash which is still ok but needs a bit more turning. Note that the bodies are completely round and there are no part lines which cut into the bolt heads. Turning the steel buffer heads and spindles takes a bit of time.

I made 24 buffers and had only I failure which was an early one before the mould had heated up. There is an undercut which will eventually tear the mould but from experience it will probably do around 40 before becoming useless. I still have the pattern so not a problem to make another mould.

Anyway 24 buffers is 6 locos worth so I won't need to cast again for a couple of months or so. :)

Ian.
 

simond

Western Thunderer
Ian

Thank you for a very informative thread. My experiences with whitemetal have been somewhat cursory, and thus unsatisfactory, I've had a bit more success with resin.

Best
Simon
 
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