Hi YouTube, my name’s Geoff and I’m the
VegOilGuy.
Since my last video on Lost Foam Casting I’ve
been spending my spare time picking the brains
of an expert and finding ways to improve my
casting technique. And look at the results.
It’s doesn’t get much better with foam.
Stick with me and I’ll show you what I’ve
learned.
Hi again guys.
In my last video you saw me make a sprocket
out of extruded foam using Green Sand. And
whilst I made mistakes on that occasion I’ve
always been pleased with the results I’ve
achieved. But after talking to a real casting
guru, I learned that these marks are known
as folds and are a common problem associated
with foam casting. Now whilst my usual results
aren’t as bad as this, on reflection I’ve
realised that I’ve often seen similar faults.
But not anymore. Thanks to my guru, a lot
of reading, dozens of experiments and lots
of head scratching, I’ve come up with a
way that will give you the crisp, perfectly
formed results you can see here.
After my last video, I received a message
from a subscriber (mountainmanfab). Amongst
other things he recommended I take a look
at a Channel by Olfoundryman. I did, I enjoyed
what I saw, I subscribed and sent off a message.
Olfoundryman wrote back answering and that
was it. Martin, his real name, is the real
deal. A typical Australian, he’s friendly,
ease going and happy to help.
Martin is a great guy and a fountain of knowledge.
What he doesn’t know isn’t worth knowing
in my eyes. I strongly recommend you check
out his channel and urge you to subscribe.
These are the real experts.
So let’s start by looking at the mistakes
in my last video.
In it I said (and I’ve read it and heard
it many times) that in lost foam casting,
the foam virtually disappears the moment it
comes into contact with the metal. Well it
doesn’t. I was wrong. It does disappear
quickly and the rate is goes is dependent
on lots of factors.
I previously said that extruded foam works
just as well as expanded foam and that’s
not strictly true. Being denser extruded foam
takes more time and energy to burn. That’s
why professionals and factories use expanded
foam.
I recommended expanding foam glue as an adhesive
and I’ve changed my mind. It seems to take
a lot of energy to burn the foam glue so I’ve
switched to something that burns more easily.
Before I made use of foam to create sprues
to feed and vent the metal which is a common
enough practice. But I’ve found a better
way which I’ll talk about in a moment.
I poured the metal through the sand, again
a common practice. But this allows the metal
to begin cooling prematurely and there’s
a better way to do it.
To rectify these problems, Martin encouraged
me to look into the process more carefully
and figure out exactly what was going on.
So beginning with the foam, what exactly is
happening?
Remember your high school Physics? Science
tell us that nothing is made or destroyed,
it only changes state, and that’s true of
lost foam. Molten metal comes into contact
with the foam and it begins to vaporise - the
foam becomes a gas. Not only that, if I’m
remember my school days correctly here, when
a solid becomes a gas it increases in volume.
That’s critical information right there.
The gas is bigger than the foam it replaces
and it’s got to go somewhere. It has to
escape the mould. If it doesn’t it will
spoil and weaken the metal. So we need to
deal with the gas.
But hang on, I’m getting ahead of myself…
how did the foam become vaporised?
The foam starts to vaporise when its temperature
exceeds 204°C (400°F). So when molten metal
gets very close to the foam or touches it,
the temperature of the foam rises and it begins
to vaporise and gas. It doesn’t instantly
vanish as many believe. Rather it retreats
from the heat source. Yes it’s very quick,
but if you’ve ever poured metal whilst lost
foam casting you may have noticed that lull
– that moment that might only be a second
but seems to take forever.
This lull is a problem. Pockets of metal can
be created by this lull and time is allowing
the metal to cool, both problems that can
spoil the process. Professionals recommend
an uninterrupted supply.
And how do we introduce the hot metal? Through
cool sand – and in my case through damp
cool sand. So before the metal near the foam
it’s begun to cool, reducing its ability
to flow and melt foam.
So to improve this process, we need to:
Keep the metal hot
Encourage the metal to flow continuously
Remove the gas
It doesn’t sound too difficult but it had
me scratching my head – until I remembered
my old friend…
Plaster.
If you’ve seen my videos lately you’ll
be beginning to think I’ve got plaster on
the brain. And I think I have. It’s cheap,
easy to work and has some wonderful qualities…
And this is the result of my plaster pondering…
a feeder made from plaster of Paris. I’ll
show you how to make these in a few minutes.
Before you dismiss this as a daft idea and
a waste of your valuable time, stick with
me.
This feeder is wide and tall, able to cope
with practically all the metal in my crucible.
Its wide mouth makes pouring a doddle.
It’s a fantastic insulator so metal poured
inside it stays hotter for longer.
The height of the metal inside the feeder
adds head pressure, forcing the metal into
the mould
It narrows at the bottom to deliver the metal
and heat just where it’s wanted.
The feeder stores hot metal as it feeds into
the mould and is the last point for the metal
to freeze, making it natural Riser
As the feeder remains open longer, it allows
gas to pass through the metal and vent
It’s really easy to make.
It can be recycled in part. It’s the second
time I’ve used this one.
We’ll see this feeder in action in a moment,
but first let’s revisit the foam.
I stated previously that to achieve greater
detail, I use extruded foam – and I still
do. I couldn’t make a sprocket like this
with expanded foam, it would lack the detail.
But as this foam is denser than expanded foam,
it’s helpful to minimise the amount used.
So
Use expanded foam wherever possible
Combine expanded and extruded to reduce the
amount of extruded overall
Hollow out sections of the extruded, replacing
the dense foam with air
With that said, I still prefer extruded foam,
but I know it’s not ideal.
I also mentioned in the last video that I
used candle wax to repair missing foam. You
can also use it to improve the detail. Even
extruded foam is bobbly and has a grain. But
you can paint molten wax onto the foam and
cut this away with a sharp blade. Here I’m
using a router bit. I’ve done all the teeth
with wax and whilst I haven’t gone mad,
they are much smoother than before and the
wax disappears easily in the foundry. You
could use this method to get very fine detail
if you have the patience.
Here you can see I’ve carved out two gates
from expanded foam. These have circular tops
to fit inside the plaster feeder and vent.
You’ll notice how they taper down to fit
the foam pattern.
I’ve glued these but for the moment I’ll
screw them as well. This helps prevent them
getting knocked off when sand is applied.
As I said beforehand, I’ve moved away from
expanding foam adhesive. I did a few simple
tests gluing up scraps of foam with different
glues and passing them through my hot wire
cutter. It’s an easy test that can yield
surprising results. Find a glue that sticks
well, doesn’t damage the foam and that burns
as easily as the foam itself.
So with the foundry fired up and melting metal
in the background, let’s make up the flasks.
Just like last time I start with a solid-bottomed
lower flask, of drag to give it its proper
name. This gets filled with green sand and
packed down well to form a flat surface. Remember
the green sand should be damp, not wet, and
if you’re not sure air on the side of dry.
You’ll see here I’ve increased the height
of my upper flask.
The foam pattern is added centrally.
Actually look carefully at the centre of the
sprocket. I cocked up here and had to cut
away a small section which I’ve patched
back in place with candlewax. See if you can
see a join when we get to the finished sprocket.
Sand is sifted initially so the finest sand
contacts the foam.
Importantly you’ll notice I’m not ramming
the sand. I’m feeling with my fingers, finding
the edges and applying pressure with just
my fingertips to the sand. You can feel the
sand compress. By touch alone you can identify
the features of the pattern. I’m making
sure I compress the sand between every tooth
and spokes, getting into all 
the details.
More sand is added until it just meets the
top of the foam gates. This is compressed
a little, but there’s no hammering force
here. It’s not wanted or needed.
Normally these screws come out with ease but
today I’m recording the process so sods
law applies. Thankfully it’s easy enough
to get them out and the holes they leave are
an added bonus.
The plaster vent is narrower than the feeder.
I cast it around a piece of copper pipe and
it fits nicely over the foam gate. The feeder
is added as well and both are supported by
sand.
Again I’ve got to stress, I am compacting
the sand but I’m not using excessive force.
The gases created by the foam will try to
vent through the sand. That’s what blackens
the sand. So if it’s too compact it can
hinder this process.
Outside now and just before the pour, you’ll
notice I’ve rested a brick on the very edge
of the feeder. There is the potential for
the weight of the pour to dislodge the feeder
from the foam. The brick prevents that occurrence.
Once last idea courtesy of Martin is to poke
a few holes in the sand. You can see the metal
spoke I’m using is quite fine and I’ve
measured the depth so that it never comes
into contact with the foam. It’s maybe half
an inch to an inch above it. The idea is steam
and gas within the sand are trying to escape.
If they find a handy hole – all the better.
You haven’t got to go mad with the holes,
maybe every two or three inches.
Before the pour a quick note about temperature.
For lost foam casting the temperature of the
metal should be greater than would be necessary
for normal lost air green sand casting. This
is because the metal has to work harder. In
lost air casting, the metal only has to fill
a void, but with lost foam casting, the metal
has to melt the foam and make its own void.
As it melts the foam, the metal gets gradually
cooler, as energy transference is taking place
with the metal to converting a solid to a
gas. If like me you can’t measure the exact
temperature of your metal, just think in terms
of getting it as hot as possible.
Here’s a handy tip. If you’re using gas
or oil to heat your foundry, when you think
you’re ready to pour, throw a few charcoal
bricks into the foundry and add the lid for
several minutes. The extra heat from the charcoal
gives the temperature a Turbo Boost.
So here’s the pour, nice and easy thanks
to the wide feeder. I don’t need to worry
about over-filling or spillage and flame and
smoke quickly plume up. Forgive the terrible
camerawork here but look at the gases passing
through the molten metal. That can only benefit
the finished work.
And here’s the results.
At a glance you might think you’re seeing
defects, but the only imperfection in this
metal sprocket are those that were in the
foam pattern. It really is as perfect a pour
as I could have hoped for.
A lot of the apparent imperfections are just
marks created by the process, mostly in the
areas where the candle wax was thickest. I
suspect these are only surface stains, some
sort of thin deposit of decomposition products
from either the foam or the wax. A quick rub
with sand paper or a file removes these but
I wanted you to see it raw. In truth I can’t
do this sprocket justice with a camera. The
texture of the foam is evident in the metal
and areas that were filled with wax are smoother
by comparison.
And the success of this process is all down
to two things… plaster and a metal spoke.
Between these two, the metal is kept hotter
for longer, it flows more freely, completely
melts the foam, fills the void and lets out
the gas. It couldn’t be easier.
It may be possible to get better results.
I know professional employ vacuums, vibration
plates, sand compression and all manner of
techniques not easily available to an average
guy, so I hope this simple combination of
ideas will work inspire you to give it a go.
If you want to see how easy it is to make
these plaster feeders, I run through that
now.
Making the plaster feeder and vent is very
simple and just requires a few things to help
cast them. I opted for a standard sealant
tube, soda cans and few other bits lying around
most homes. Other than that’s it’s mainly
plaster of Paris, water and a little bit of
time.
I found that a sealant tube made a nice feeder
size and by enclosing it in an ordinary soda
can I could surround it with a reasonable
thickness of plaster of Paris. Originally
I made flat-bottomed feeders. But Martin was
able to spot potential problems resulting
from this and he suggested a cone-shaped bottom
of at least 45 degrees which is the only tricky
bit.
So I took a chunk of MDF, used a hole saw
to cut something close to the diameter of
a soda can, mounted it in my drill press and
with a block and sandpaper tapered the sides.
A step drill bored out the inside and I ended
up with this.
However we live and learn and whilst you’ll
see me using my MDF cone, I’d recommend
making one from plaster. It’s quick, easy
to shape and won’t stick to the silicone
mould you’re about to see made.
Satisfied that the cone was the right size
and shape, I built a simple box out of MDF,
and again I think ordinary wood may have been
a better choice. A lid and bottom were easily
made and I used some long bolts to hold everything
together. Finally I made a small cylinder
plug that fits the diameter of the cone. The
purpose of this plug is to position and hold
the cone inside the box, or rather mould,
which is what it is.
I wet everything thoroughly with cold soapy
water then squirted in some ordinary silicone
sealant. Soapy water is one thing that silicone
doesn’t stick too. The problem is of course
water also swells MDF… hence my recommendation
that you use plaster. Make sure there’s
no gaps between the cone and the walls and
bottom of the mould box. Tidy up the silicone
a little then leave it at least 24 hours in
the warm and dry.
The following day I trimmed away the excess
silicone. I removed the plug from the cone
but left the cone in place.
I placed a bolt through the top of the lid
and covered this with silicone. I wet what
I didn’t want to stick then filled the core
of the cone with silicone. I squashed the
lid on and added some weight. The lid should
have fitted flush, but the silicone cone had
swollen. This needed leaving 24 hours.
The following day I pulled everything apart
and removed the MDF cone, leaving me with
this. It’s a bit rustic, but it’s a surprisingly
effective mould.
I mixed up some plaster of Paris, added the
lid and waited an hour.
The result was a crude but usable cone. It
needed a little tidying up, but thanks to
the mould I can now make as many cones as
I need.
With the cone still damp, cut away to top
of a soda can with scissors and drop the cone
inside.
I’ve found that the sealant tube can be
awkward to pull free, so I used more soda
cans and made so simple sleeves, held loosely
with tape.
I added a little PVA for good measure then
inserted the sealant tube nice and centrally.
It’s then just a matter of pouring plaster
of Paris into the gap, hopefully not making
as much mess as me.
Half an hour later and everything should pull
apart. Getting the soda can off is no easy
task, but if you’re careful you can peel
it like an orange. Don’t peel away too much
at this stage. I find it helpful to slightly
taper the upper edges at this point. You can
then slide another can on top, insert the
sealant tube, and repeat the process again.
Give it half an hour, peel away the top can,
chamfer the edges of the plaster of Paris,
add another can and fill that.
Eventually you’ll be left with something
like this. Let it dry ideally for a week or
so and then place it in your oven at a shade
over 100°C to bake out any water. After a
couple of hours, turn the heat up to 200°C
as, apparently, there’s still water present.
Jewellers bake their plaster for hours on
end at temperatures way above these. And that’s
your plaster feeder finished.
The vent is easier still. A chunk of foam
makes a nice base. Push a piece of copper
pipe into this. Then push a piece of plastic
waste pipe around that. Notice that I’ve
cut a crude split in the plastic tape which
would need to be covered by masking tape of
similar. Plaster of Paris is poured in the
gap and the whole thing is best left a couple
of days as the plaster does swell a little
when wet, making pulling the copper pipe free
tricky until it’s shrunk back.
And that’s it guys, a finished video. I
hope you give these plaster feeders a try.
It’s made an incredible difference to the
precision of my casting. As always, if you
haven’t subscribed yet, please do. Any comments
or questions, just drop me a line. So take
care and thanks for watching.
