Hi guys,
If you were with me last time, you’ll remember
I had a go at casting a Celtic Knot using
the Lost PLA method, taking an ordinary 3D
print and casting it in metal. I also had
a go at multiple casting, trying to cast 5
of these at once.
Now that failed… I only got one good cast
out of 5. So today I thought I’d try again,
still using a 3D printer and the Lost PLA
method, but this time taking inspiration from
the Jewellery trade and making a Casting Tree.
It’s not just the Jewellery trade that use
this method. A friend of mine, John Dersch,
creates some amazing ornamental castings for
modelling enthusiasts, and he uses this technique.
Look at this amazing example of a casting
tree.
There’s no way I could do something so intricate,
but I wanted to have a go, so I turned to
Fusion 360 and had a bash and designing the
trunk of the tree that could fit 12 patterns.
These holes are sunk in at 45 degrees.
I needed small branches to fit into these
and again these were easy enough to design
and print, though when it’s this small,
it’s not exactly a perfect print… but
it will work.
I’m sticking with the Celtic Knots from
last time, but for spacing, these needed to
be just a little bit smaller to fit inside
my steel flask.
Each small branch is attached to the back
of the pattern with a couple of tiny dabs
of this positioning wax. It’s nice and sticky
and surprisingly strong.
Even though I shrank the size of the Knots,
they’re still quite large by jewellery standards
and they also took a long time to print. So
I resized the Celtic Cross I made a few weeks
earlier and I was amazed how nice and cute
these look at this size.
Eventually everything was pushed in place
which was a little fiddly, but not difficult.
You’ll also see that I wrapped a small amount
of wax around the join between branch and
trunk to ensure a good watertight connection.
The metal flask slid on beautifully leaving
a good amount of room on all sides.
It was then just a matter of mixing up the
Investment casting Plaster, filling the flask
and letting it set for a couple of hours.
Then it was cooked according to the plaster
manufacturer’s instructions. During this
time, the PLA melts out of the plaster and
leaves a void ready to be filled by molten
metal.
Once fully cooked, it was time to melt some
metal.
The flask was placed on my home made vacuum
system and it’s still very hot inside, around
600 degrees Celsius. You can just about see
the gauge is registering the vacuum.
The pour went well and then it was just a
matter of waiting a good hour for the metal
to cool.
The 
plunge in cold water was unexciting. This
meant scrapping away soggy plaster with my
fingers to get to the casting.
And look at that…
After a scrub in some hot soapy water, here’s
the result.
The pouring basin came off in the bucket and
I think one of the Knots did as well. One
of the knots came off whilst I was scrubbing
the casting clean, which shows you how thin
the connections are.
The trunk seems to have taken a battering,
being a little hollow in places, and I’m
beginning to think that’s something to do
with the vacuum. But at this point I was beginning
to think I had 11 good castings.
An old pair of wire cutters separated everything
from the trunk and things still looked good.
Another dunk in some soapy water removed the
remaining plaster and do you know what, I
really do have 11 good castings. I think there’d
be 12 if I could be bothered to scour through
my sludge bucket.
And if you’re thinking they look a little
rough, remember how magnified they are on
your screen. I think they’re every bit as
good as the original 3D prints. I know not
everyone likes to see the print pattern, but
it’s there for a reason – it’s there
to show just how much detail can be captured
in the metal using this technique. It’s
still amazes me.
Now I’m done here - it was just an experiment
- but to prove how easily these can be cleaned
up, I’ll just rub down a couple with sand
paper. I won’t make a fuss, but you should
see there’s perfects castings here.
So if you fancy a little mass production,
it’s possible to create a casting tree with
the Lost PLA method. And it seems those jewellers
and ornamental casters are correct using this
set up. You can’t get much better than a
100% success rate – if we ignore the one
that’s still in my sludge bucket.
So I hope you enjoyed this one guys and if
you did, please like it. Check out my other
videos and please subscribe to my YouTube
channel if you haven’t already. Do send
in your comments and questions as it’s always
great to hear from you guys. So that’s it
for now, take care, and thanks for watching.
