Hi YouTube, my name’s Geoff and I’m the
VegOilGuy. If you’ve been watching my videos lately,
you’ll have seen my ongoing battle with Lost Wax Casting.
The one persistent comment I’ve had since trying starting this is “use a vacuum.”
Some of you have even been observant enough to say, “Hey, you’ve got a vacuum pump.
Why aren’t you using it?” Well this pump cost me a lot of money… more
than I wanted to spend in honesty. And whilst it’s very good, it cannot be exposed to
heat… and molten metal is pretty hot. So I wondered if I could make my own vacuum
system… and that’s what I’ll be doing today.
I started out with a couple of purchases, and a big thanks to those contributors who’ve
been kind enough to make donations. It really is a big help.
I bought this solid stainless steel flask. It was a fifth of the price of the perforated
flasks so I thought I’d give it a go. I also bought this injection wax, and it’s
brilliant. Honestly… I can’t praise it enough.
If you saw the very first casting challenge, you’ll remember I tried to cast a coin and
this is the silicone mould I made. However, the wax coins I produced were far
from ideal. But things were different with this wax.
I poured some of the pellets in an empty food can and heated them gently on this electric
hob until they’d melted. Then I placed a plastic syringe inside to acclimatise. The
wax isn’t hot enough to melt the syringe but if the syringe isn’t pre-heated the
wax will freeze instantly. After a few minutes, a small amount of wax
is drawn up the syringe and then injected into the mould. It’s important not to pull
the syringe out too quickly, but to give the wax a few seconds to begin to solidify.
A few minutes later, the mould was opened up and look at that. What an amazing wax pattern.
This was my first ever try with this wax and I can’t fault it. I think these horizontal
lines are caused by the force of the syringe. It’s too large really. A smaller syringe
would have been more controllable. And if you’re wondering what all the other lines
are, they’re tool marks. This mould was made from a 3D print and I wanted to keep
these marks – I wanted to test the ability of wax casting to pick up very fine detail.
I decided to try this injection wax as a pouring wax. Even in an open mould, without any fuss,
it produced beautiful results. Yes, I could have taken more time and got something a little
better, but for today’s experiment, these will do, especially if we remember exactly
what these faults were. I was so impressed with this wax that I honestly
didn’t want to introduce another sort, so I made a few crude sprues from this wax and
made a wax tree. With the tree on an old tin lid, the steel
flask slides over with too much room to spare if I’m honest. But better too big than too
small. I surrounded the base with plasticine, or
modelling clay, whatever you call it, as this makes it water tight.
I then mixed up some investment plaster, mixing this well for around 3 minutes in line with
the manufacturer’s instructions. I then vacuumed this is my vacuum chamber to remove
excess air, poured the content into the tube, and discovered I hadn’t quite mixed up enough.
Typical. But this stuff goes off too fast to mess around
so I turned on my vacuum pump and removed any air that had become trapped during the
pour. After it had set, around 10 minutes later, I topped off with a little more plaster
to make sure everything was covered. Two hours later, I pulled the plasticine from
around the rim, scraped away any loose plaster, then gently prized the wax from the lid. I
love the way it had captured the ink from the barcode beneath it.
This was then placed in my foundry at 80°C for an hour to gently cook out the wax.
A few weeks ago, I shared with you a homemade vacuum chamber, made from cheap plumbing parts
and bits of plywood. I wondered if I could use this to vacuum molten metal. Well there’s
no way I could place a red-hot flask inside a wooden box, but maybe I could place one
on top… I took the clear plastic lid and cast a silicone
circle on top of this. Silicone is actually pretty good with heat and can withstand up
to around 300°C without fuss. I drilled a small hole centrally and planned
not to lift the silicone. But the debris from the drill got stuck beneath this so I had
no choice, though this type of silicone doesn’t like sticking to anything, so lifting it was
easy. I cleared the dust and re-aligned everything.
Now I had somewhere that I could place the flask.
I grabbed the hand-made piston pump I created at the same time as the Vacuum Chamber, and
I hooked this up. I placed a food can on top of the silicone pad and got pumping.
Almost immediately the gauge started to register the vacuum, and when I tried to lift the food
can free, it was stuck firmly thanks to the power of the vacuum.
It’s worth noting that this vacuum chamber has sprung a leak. Over around 20 seconds
or so it will lose vacuum. Whether this is the silicone seal, the valves or the plumbing
I just can’t be sure as it’s so small a leak I can’t detect it. But it does mean
extra pumping to maintain the vacuum. Additionally this chamber is around 8 inches
square inside and whilst it’s quick enough to empty of air, it could make it quicker.
So I came up with a simple solution. This is my lazy bucket. When I’ve finished
casting I tend to throw in bits of plaster, metal and other debris left over from my tinkering’s.
I always keep my McDonalds drink cartons as they make useful mixing cups, and four of
these would be ideal for my next idea. I gathered the plastery debris and added some
water to this as I knew it would be thirsty for moisture. After a few minutes, I poured
away the excess water, leaving a sludgy mess. I then mixed up some very watery plaster of
Paris. A little Plaster of Paris goes into the cup.
Then it’s mostly filled with debris. Then I topped off with more Plaster of Paris and
tapped everything to settle out the content. Strange how it looks like a McDonald’s milk
shake. These set within half an hour and four of
these fill my vacuum chamber. This drastically reduces the airs I need to displace.
With the lid on and a paint tin on the silicone pad, a quick pump test showed a much faster
response. It was now ready to try with metal. Now, a couple of important points…
Firstly, the plaster flask was cooked according to the manufacturer’s instructions, but
this time I raised it to 700°C. I then took this out of my foundry and covered it with
fire bricks allowing it to cool, but slower than it would have done.
Secondly, a few of you guys have been asking about my metal preparation. So just to clarify,
I heat my metal thoroughly and remove any dross. I then add de-drossing flux and then
remove the dross. After this I use sodium crystals to de-gas. Some folks might not like
that, but it was a tip Myfordboy gave me and it seems to help. After that, I find I need
to de-dross one more time and I’m ready to pour
My metal was ready in my electric foundry. I placed the flask on top of the silicone
pad and registered a temperature a little over 100°C. I measured the temperature of
the plaster and this was still a little over 200°C. So I have not maintained the flask
at the same temperature as the metal, which I am aware is the convention.
I took the crucible from my foundry and poured this into the plaster flask. It’s a nice
shade of pink as I wanted it hot, around 700°C. I quickly but safely put the crucible down
and got pumping. Did you see that? Let me show you again…
Watch the metal as I begin to pump… it actually gets drawn down. You can see to metal visibly
shrink. It’s not much, but it’s there. That’s the power of vacuum.
To be honest I never noticed this at the time as my eyes were glued to the gauge. And I
didn’t want to stop pumping until the metal had frozen.
Once it had, which took a couple of minutes, I dunked the content into a bucket of water.
Eventually most of the plaster was washed away and I actually swore… I was genuinely
taken aback. After a little more clean up, this is was
the result. Now if you’re not as amazed as I am, I think
you may be missing the point. These may not be the prettiest coins you’ve ever seen,
but what they are is highly detailed castings that are virtually identical to the wax patterns.
There’s no pockets. There’s no porosity.
Every flaw your eyes are detecting was also evident on the wax patterns.
The vacuum chamber had done it. It had produced a near perfect casting… or at least as perfect
as I think I can achieve. There are some strange straggly bits. Maybe
there was too much vacuum pressure, I don’t know, and on just one of the coins there was
a strange peel-like flaw. It was so thin it could be easily ground away, and its shape
is echoed in the other coin. Maybe there’s a fault with the mould. Or maybe it’s just
because I filled these two so casually, almost without care.
If you’re wondering how all this works… The pump makes use of two one-way check valves
to draw air in one direction only, creating a vacuum in the chamber. As there’s a hole
in the lid, this vacuum is extended into the plaster flask. Casting investment is specially
formulated to be porous. The vacuum sucks on the metal – or perhaps more correctly
the changing air pressure pushes the metal down. But let’s not try any of that science
stuff. Let’s just bask in the glory of these precise castings, easily achieved with a homemade
PVC pump and a homemade vacuum chamber. Now let me tell you something really impressive…
both the pump and the chamber were built for less than one of those perforated flasks would
have cost me. And I could have bought 6 or 7 of those same flasks with the money that
I spent on my vacuum pump. So here is a truly cheap, easy build solution
to your lost wax casting troubles. I honestly cannot tell you how delighted I am with it.
Sometimes simple really is brilliant. For details of the homemade chamber and pump,
look to the vacuum chamber video. It’s very easy to do.
It looks like lost wax casting just got a whole lot easier for me. One thing’s for
sure, you can be certain there’ll never be anything small and detailed in the casting
challenge again, because if there is, I’ll be kicking backside!
Talking of which – that’s the casting challenge and not backsides – we have a
third challenger now. BigstackD is planning to join our next casting challenge in early
September. Both Perry and myself are looking forward to Bigstack’s unique take on things
and no doubt the challenge is going to get even better. I can tell you what we’re casting
next time. It’s absolutely brilliant. We’ll all be having a go at casting…
…though the strawberries and kangaroo meat will be optional.
And I think we can call that a finished video. I hope you enjoyed this one guys, and if you
did, please like it. If you haven’t subscribed yet, then please do. Look out for my other
videos on my YouTube Channel and check out my website.
So that’s it for now guys. Take care and thanks for watching.