Hi YouTube, my name’s Geoff and I’m the
VegOilGuy. My son asked me to cast him an Overwatch coin
the other day and I’ll be honest I wasn’t sure what that was. So for those like me,
Overwatch is a phenomenally popular team-based game by Blizzard Entertainment. And I think
I can see the appeal… This is an Overwatch Coin and that’s what
I’ll me making today. Now there are already versions of this out
there in Thingyverse, but for me they all seemed a little large for a coin, so I made
my own STL file using Design Spark Mechanical, which is free software.
I don’t own a 3D Printer but I was able to get the coin printed at 3D Hubs and here
it is… And any normal parent would leave it there,
but I don’t need many excuses to do a little metal casting, so I sanded this down and added
a little car body filler in places. I’m still fighting an on-going battle with
Lost Wax Casting, so my next step was to produce a silicone mould.
I took the top of an aerosol can and drilled a finger sized hole in it, then stuck the
3D coin over this with some plasticine, modelling clay, whatever you call it. This should keep
things watertight but allows me to push the silicone out once set.
I mixed up some mound making silicone and poured this on, then placed it in my vacuum
chamber to pull out all the bubbles. The next day I pushed out the silicone mould
and trimmed away the excess. I then heated this with a hairdryer.
Then I poured in some molten casting wax. I swilled this around for a few seconds and
then emptied it. I let this cool for a few moments and then
repeated the process until all the detail was filled.
After this wax was topped off and allowed to set, I was able to pull out a wax pattern.
Well actually I did four in total because today you’re getting a three for one – I
decided to do three casting experiments at once. I made one extra coin just in case.
With the first coin, I moulded this teardrop shape lump of wax.
I applied the heat from a soldering iron across it and was able to produce this pouring basin.
By rolling up the metal from a drinks can, I was able to mould this tapered sprue from
wax. Using the heat of an alcohol burner, I melted
a couple of wax sprues to the back of the first coin.
Then everything got attached to a scrap board. So there’s the pouring basin, leading down
to a tapered sprue, which in turn attaches via a gentle curve to the coin, which is attached
to a vent. Now the wax coin wasn’t perfect. Like all the coins it had some small wax repairs.
This arrangement was surrounded by an ordinary food can and then by plaster investment.
The other two coins were placed on another board, face up. These were eventually surrounded
by plastic from a piece of rainwater pipe and again filled with plaster.
The investment plaster is mixed according the manufacturer’s instructions and then
allowed to set for two hours. All went well this the food can.
One of the two coins came out nicely. Unfortunately the other was a disaster, tearing
away the plaster and wax. And even on a second attempt, the same problem occurred. So one
of the coins will never be perfect. But there’s enough detail there for this experiment.
The three plaster flasks were heated in my foundry at 100 degrees Celsius for about half
an hour until all the wax had been emptied out. After this the plaster moulds were cooked
according to the manufacturer’s instructions. It was then time to melt some metal in my
home made electric foundry. Now I received a question this week from someone
asking about metals. He said he’d noticed that ingots were quite expensive and wanted
to try the hobby but was put off by this. So I just thought I’d remind everyone, you
can buy ingots if you have the money, but personally I think that’s the choice of
the professional. Most amateurs, myself included, make use of whatever scraps we can get our
hands on, and these are generally free. I’ve melted down thousands of drinks cans to get
at the free metal inside them, and whilst this is definitely not the best quality metal
you’re going to get, for amateurs, for newbies and for those who like free, it’s still
a very good choice. Getting back to the casting, filling the wooden
flasks with sand was going to be tricky as I planned on using two methods in one flask
– the conventional basin and tapered sprue approach, and my slap-it-in-and-see plaster
feeder approach. So I weighted the drag in place and used a scrap of card to determine
the centres of the plaster moulds. Even though this was fiddly, it was important.
I then added green sand and packed this carefully around the plaster patterns with my fingers,
compressing the sand gently so that it firmed up and gripped the plaster shapes.
Once I was happy the sand was binding things nicely, I was able to remove the weights and
add more sand. I was then able to gently ram with the handle
of my rubber mallet. Remember, there’s no need to ram this sand too hard. Its job is
to hold the plaster patterns in place and it will do with without excessive ramming.
The drag was eventually fully filled with sand and this was scraped level before being
placed to one side. Working on the cope now, I weighted down the
corners again to help keep things stable, then used the same cardboard jig to work out
where the centre of the plaster patterns was, marking this with a pen.
The coin is very small so I felt that vents would be unnecessary, but I used one of my
plaster of Paris vents to act as a feeder. I taped this help prevent the plaster from
absorbing moisture from the sand and the pink paper cover helps keep out sand.
This is a tapered sprue I made especially. I felt a bit like Harry Potter if I’m honest.
I repositioned this a couple of times before I was happy.
I filled in with more green sand and packed things down as best I could.
Once filled, I scraped the top level. The cope was gently placed on top of the drag
and the sprue was pushed down slightly to mark the sand beneath.
I then separated the two halves of the flask. I cut a small runner from the base of the
sprue over to one of the coins, in this case the less detailed one.
I firmed the sand with my fingers. I lowered the cope back down and pulled free
the tapered sprue. I used a chunk of plastic pipe to core out
a basic basin shape. I then joined this to the sprue and created
a gently curved ridge with my fingers. A little low-pressured air cleared away the
loose sand. The plaster had marked the sand above it which
allowed me to create a runner from the sprue. I test fitted the drag and cope together a
few times to clear away any loose sand, blow this clean with air, then everything was fitted
together ready for the pour. And here you can see everything in place.
Here is the traditional full plaster encasement approach.
This is non-traditional half plaster in green sand with basin and tapered sprue approach.
And this is my definitely not traditional half plaster, plaster feeder slap-it-in-and-see
approach. The metal was nice and hot inside my electric
foundry and it was time to pour. First the sand basin. That seemed to work
okay, flowing from the basin, over the rounded ridge and down into the tapered sprue.
Next was the canned coin. The metal went into the basin and over the ridge, but I couldn’t
be sure anything had gone down the sprue. Certainly nothing popped up the small vent.
Last was my plaster feeder and that one demanded attention. There was liquid metal chaos as
gasses and metal competed for space at the bottom. There’s certainly something trying
to get out of that metal. I suspect using one of my plaster vents instead of the much
wider feeders caused this volcano like reaction – lots of energy in a confined space and
no way out but up. Just a few minutes later, I took the canned
coin and plunged it into water. I like this bit.
The hot plaster tears itself apart within the water and it’s much better than hammering
on cold plaster. A few seconds later a not too shabby casting
was revealed. It looked nice and smooth, free of pockets or bubbles.
I waited a good hour before pulling the wooded flask apart.
And things weren’t looking too bad with the coins.
I dug out my slap-it-and-see coin and I was pleasantly surprised. The other coin, even
though it was from a spoiled plaster mould, still didn’t look so great.
With everything brushed and washed free of plaster and sand, I was able to take a closer
look. The full plaster encasement, the traditional
approach, looked quite nice. Remember I’ve had bad experiences so far, but this time
I added the basin and sprue to this – which is definitely NOT traditional in this situation.
But I think it’s served the process nicely. I suspect the pour was gentle and slow and
everything looks clean. No pockets. No porosity. There’s a tiny hint of detail, but not much.
Hardly any really. The vent did work but froze before hitting the surface and you can really
see that classic basin and sprue set up. Next is the basin and sprue in sand coin.
Now whilst this was never destined to be great because of the spoiled plaster mould, there’s
more going on than that. That’s either a lot of sand or a lot of porosity, and I was
very careful about the sand this time. The basin and sprue look pretty good, so that
worked okay, and the drop isn’t much more than 50mm in line with Campbell’s casting
rules. But it hasn’t worked for me here. Last is my slap-it-in coin and I am being
deliberately flippant about the name, but the results are quite shocking. Look at the
detail here. By far the best of the three. There looks a little roughness, but those
are actually wax repairs. And yes there is either sand or porosity, but much less that
the last coin. I realise some of those pockets might look large and deep, but remember this
is very close up on something that’s really quite small. Looking from the side, that frenzied
activity is clear in the metal at the top, but it’s much smoother and calmer at the
bottom. And people are going to argue that the plaster feeder contained water and again
I’ll counter argue that the plaster was cooked at 230 degrees Celsius, driving off
by far most of the water. Whatever tiny bit remained pales to insignificance when compared
to the water in the sand. Whatever is taking place, my approach won
the day here and there was only one coin worth cleaning up and using.
It took very little rubbing down on some sandpaper and a file across the edges to produce something
looking not too shabby. All it needed then was a little black and
gold paint. And here it is. Again the scale of the screen
spoils things a little because in life this coin looks quite nice, but there are imperfections
I’ll admit. But this was nevertheless an interesting little project that enable me
to test three more techniques on my quest for Lost Wax Casting perfection. Who knows,
maybe one day I’ll get there, but in the meantime for me this is a nice result.
I certainly hope you enjoyed this one guys and if you did, please like it. Please share
this video with your YouTube buddies and subscribe if you haven’t already. Check out my other
videos on my YouTube Channel and have a look at my website.
In the meantime guys, that’s it for now, take care and thanks for watching.