Hi YouTube, my name’s Geoff and I’m the VegOilGuy.
A while ago now I shared a Green Sand Lost Foam Casting technique with you and showed
how the process can be greatly simplified using these simple plaster of Paris vents
and feeders. It’s proved to be very popular and a lot of you guys have written to me talking
about your successes. Unfortunately I did rush through the vent
and feeder making process and I have had a number of requests to cover this topic more
fully. As I’m going to be doing some more casting videos soon, I thought now was a good
time to do just that. I’ve tried to find easier construction techniques
which I’ll show you now and I’ll also cover how to make and use a silicone mold.
Let’s start with the vent. Shopping on eBay, I found these candles. A
box of 25 worked out around 50p each which is nice and cheap and they’re ideal for
my purpose. This is a 1 ½ inch (40mm) waste pipe. It’s
a bit old and it’s been chewed by my dog, but it’s fine for what I need today.
This is plastic cut from a used veg oil container, but you could just as easily use an ordinary
plastic bottle, so I’ll use both. The plastic bottle needs to be cut to be roughly
the same length as the candle. The top of the bottle makes a useful funnel,
especially if you cut the screw section off as I did – using an ordinary hacksaw.
This is extruded foam – but ordinary white expanded foam would works too. The pipe is
firmly pushed into this and it carves out a useful circular hole.
This tapered end on the candle makes it easier to push the candle centrally into the foam.
The plastic is then wrapped tightly around the pipe and held in place with rubber bands.
Once slid from the pipe, this then sits nicely in the foam and the candle is placed in its
hole. With the funnel fitted, plaster of Paris a
little on the thick side is poured in. I guess there wasn’t quite as much of a gap as I’d
thought, but a little light agitation sends the plaster into the plastic sleeve. Tapping
the sides removes any trapped air and the candle gets centralised by eye. It can float
up, so make sure it’s well seated. After an hour the sleeve is twisted from the
foam base and the rubber bands are removed. Then it’s simply a case of unwrapping the
plastic. All that remains now is to free the candle
and make the actual vent, but the plaster needs to dry out first. Leave it a good couple
of days at warm room temperature. When ready, place it in your oven in such
a way as you can catch the dripping wax. Here I’ve placed 3 on a simple foil drip tray,
angled slightly forward and funnelled into an old drinks can. I’m going to keep the
wax as I’ve already got uses in mind. Once the wax stops dripping, it’s done for
now. After a little clean up with sandpaper, here’s
the result… a simple hollow plaster tube ideal for a vent. I find it best to make several
of these and keep them handy for when I’m casting.
Now let’s look at the feeder. Last time I went with a standard sealant tube for an
internal diameter and I will again now, but the cut-away-can idea was a little tricky.
So instead we can use plastic again. But first let’s start with the bottom of
the feeder. For this shape we’ll need to make a cone pattern and a silicone mold, and
the mold starts with a simple box. I used MDF as I had plenty of scraps and it’s
easy to work with. The top and bottom are 5 inches square and the sides are 5 inches
less the thickness of the MDF. The height of these sides is twice the thickness of the
MDF. I’ve also got some small scraps for corner supports.
These sides and corner supports are glued together with a good waterproof glue. At the
same time I glued up some more scraps that will make a cone. For now it just needs to
be a square just over 3 inches wide and the depth of two thicknesses of the MDF.
I want the silicone mold to stay inside the mold box and in my last build the silicone
did come out. So this time I added a couple of small wooden sections to help grip the
silicone. The top and bottom of the mold box need to
be fixed with bolts, so I carefully drilled four corner holes. To help with future alignment,
a marker pen is used to add witness marks. A fifth hole was then drilled dead centre
and another bolt inserted through. With the mold box completed, it’s time to
make the cone pattern. The width of a drinks can seems ideal so that’s the ideal measurement.
You can see I’ve drilled a 12mm (half inch) hole in the centre and through this goes a
length of 12mm thread rod. If you’ve got thicker stuff to hand, use it, but don’t
go thinner. Some washers and nuts are very securely tightened
either side. These must be tight for what comes next.
I’m going to be turning this to make a cylinder and then a cone, so it would be helpful to
remove the corners. This could be done with a hand or chop saw, but I’ve got this wood
carving disc that I’m enjoying experimenting with, so I’ll be using an angle grinder.
I haven’t got a lathe but I have got a drill press. With one end firmly clamped in the
chuck, a couple of test spins show all seems stable. So I turn on the drill and everything
spins nicely. Again I’m using the angle grinder and this
wood cutting disc, but you could use an angle grinder with an abrasive disc, a belt sander
or even a block of wood and coarse paper. Initially I just want to remove material.
The trick is to be VERY light with your touch and make sure you go with the rotation of
the work and not against it. The more circular the wood is before you start, the easier this
will be. But with just a little care, it doesn’t take long to form a cylinder shape.
Now you might be thinking this looks a terrible mess, but the blade has done a fair job of
removing a lot of material very quickly. A block and sand paper clean this up very quickly.
Here I’m offering up a piece of rainwater pipe that’s pretty close to the size of
a can, but I should really be using callipers to take accurate measurements.
A little more material needs to be removed, so the process is carefully repeated until
the work is nearly there. At that point I start forming the cone shape
and now the material really starts to fly, so eye protection or a face guard are a must,
plus a good mask as MDF dust is nasty stuff. After a bit of sanding, it’s a nice fit
and it will be good to go. To hollow out the inside of the cone, I used
a step drill. This does require a firm grip so be careful, but otherwise take your time
and let the drill bit do the work. The drill bit leaves ridges but these can
be removed with a round bar and some sand paper.
Last time I used water to stop the silicone sticking, but this caused the MDF to swell.
So this time everything is finely sanded and three coats of fast drying varnish are applied,
with a fine sanding between each coat to remove all the brush marks.
Ron, one of my subscribers, recommended using car or furniture wax as a mold release agent,
so every surface has been given several coats of car polish except the insides where I want
the silicone to stick. I wish you could feel the difference. Everything is slick, shiny
and – yes – slippery. If nothing else, this layer of wax will further
help seal the MDF to prevent moisture problems. I decided at this point to add a few holes
to allow the silicone to escape when compressed. The last thing we need is a plug. Again this
was made on the drill press in a similar way to the cone. Its job it to hold the cone centrally
during the mold making process. This is actually the plug from last time and it’s a little
loose, so I wrapped some tape around it. It needs to be snug but not tight.
A little research showed me that some mold makers apply petroleum jelly to their molds
to prevent silicone sticking. So that’s what I did… every mating surface… everywhere
I didn’t want to stick. I even put thin coat on the bolts.
This is just ordinary silicone… nothing special. It’s squirted around all the edges,
up the sides and across most of the bottom, but avoiding where the cone will be inserted.
Silicone is then added to the sides of the cone and the cone is inserted into the box.
It’s twisted to helps remove air pockets. The nozzle is then pushed in deeply and more
silicone squirted in. The idea is to remove all voids.
Once finished, a wetted finger pats down the top to squeeze everything in place and then
a tiny bit more silicone added for good measure. The lid is pushed on firmly and the nuts are
well greased, screwed tightly home. Some silicone will squirt out of the top and sides so be
prepared for a mess. Everything should then be placed in a warm place for 24 hours.
The next day the bolts were removed and I used a sharp blade to cut away any unwanted
excess, then carefully prised the blade between the top and bottom. I actually tapped the
blade with a wooden stick at times, but there’s very little force involved. It’s just a
matter of breaking the join. You could of course use the whole knife and should, but
I’m daft like that. The top and bottom can then be twisted free
and I’m very pleased with the results. But there’s a lot of silicone here and it needs
to dry out more. So another 24 hours in a warm spot is called for.
The next day everything was been cleaned up a little. This was very easy with a sharp
blade. There’s one little fault which you can see
here and I can fill this during the next step. It was caused by the drilled holes so I filled
the corresponding hole above this point. I also filled the bottom centre hole as I don’t
want silicone leaking out there. Notice that the top and bottom have been cleaned
and waxed again. But the male section of the mold needs to stick to the lid of the box,
so on the underside a small circle is scraped clean of wax and varnish with coarse sandpaper.
A small bolt is inserted into the lid. This is tightened securely and has a number of
large washers added to help the silicone grip and form the male part of the mold.
Once again everywhere that I don’t want to stick is covered in a thin layer of petroleum
jelly and this time that means everything except the small circle and the bolt. Even
the silicone is coated as silicone is quite happy to stick to itself.
Then silicone was squirted into all the nooks and crannies of the bolt, then the cone was
filled. Some silicone was squeezed in the imperfection.
At that point the lid was squeezed on and the bolts tightened once more.
I left it 48 hours before risking pulling things apart. Again it was necessary to split
the edges open, but once everything was finally parted, the bottom that came off easily, then
I massaged around the cone a little to try and break any join.
With a final twist the lid came off and it was a good result. It may initially look a
mess, but these are fine strands of silicone sandwiched between the jelly. A little clean-up
was necessary, including cutting away this misshapen section, but the overall result
was pretty good. And as you’ve probably guessed, I left this
whole thing another 24 hours to ensure it was dry enough to use, and that completes
the mold. Now comes using it. The bottom of the box isn’t really needed
now. I make use of another strip of plastic. It’s worth noting, again I covered everything
with a thin coat of jelly. It really seems to help.
Some plaster of Paris was mixed up, again a little stiff, and the void slightly over-filled,
and that’s what you want. Experience has taught me that if you under fill, anticipating
the size of the other half of the mold, there are invariably voids and imperfections. Better
to over fill and squeeze too much out. I made note of the witness marks but didn’t
bother with the bolts. Instead some weight was added to the lid.
I left this an hour and lifted the box from the plastic.
I then twisted the top revealing a nice inner cone shape and very little excess plaster
thanks to the jelly. A gentle push from underneath and out it popped, a little ragged around
the edges but otherwise perfect for use. I was now ready to add the sides and as stated
earlier an empty silicone tube is ideal. But to help alignment, I added plaster of Paris
to the inside of the cone pattern, and yes I did apply jelly first, then stood the tube
on end and centralised it by eye. Once this had set for an hour, I removed it, gave it
24 hours to dry, then sanded it lightly so that it fit comfortably back inside the cone.
I also gave it several coats of PVA as plaster on plaster tends to stick very quickly.
With the cone also lightly sanded to remove burs, it’s time to form the outside with
more plastic. A beer can works best for this and ironically my favourite brand just happens
to be the exact dimensions required – at least that’s what I tell my wife. Some more
plastic is wrapped around the can and a rubber band secures it. The can is then slid out
and the cone slid in. The can may be used to push the cone all the
way to the bottom if necessary and the rubber band provides a flexible seal. The can should
then be chilled to ideal temperature and the content drunk at your earliest convenience.
This isn’t a necessary part of the build, but it certainly helps me enjoy it.
More plastic is cut and this gets wrapped around the silicone tube.
The seam is taped lengthwise to hold the plastic in position. Don’t overwrap the plastic
in tape this time as that may make removal difficult later.
Thanks to the plaster nozzle at the end of the tube, the tube sits centrally inside the
plaster cone, leaving a fairly even gap all around. Notice that I’ve added more rubber
bands here as well, though none of these are strong enough to crush the shape, just hold
it. Everything is placed onto the same small piece
of plastic and the sides are squeezed gently to allow plaster of Paris to be poured in.
Again it’s a little on the thick side. The sides are tapped to remove air bubbles
and allow everything to settle. An hour later, the rubber bands are removed
and the plastic outer shell is removed and washed ready for next time. Poking a finger
through the hole at the bottom, it’s easy to push the out the cone, though the outer
plastic shell stays behind. And that’s why you didn’t use much tape. The shell is plastic
and doesn’t bond well, but tape would glue itself in place. Gripping the inner top corner
of the plastic, it’s turned as if the rotate it and sure enough the plastic core pulls
free ready for cleaning and reuse. What’s left is a plaster cylinder with a funnel shaped
bottom. It’s best to give it a couple of days in
a warm spot to dry out and here it is tidied up a little with a little sand paper.
So that’s the feeder and vents finished, but there is one more thing. Our resident
casting Guru, Martin the Olfoundryman, has informed me that plaster retains water. He’s
a clever bloke, a true professional, and really knows his stuff. He’s quoted chemical formulas
at me until I went glassy eyed and started to dribble, but the crux of the matter is
that these plaster feeders and vents of mine should be baked in an oven before use and
heated slowly, over a number of hours, until they reache 400C. Now I do bake mine to 200°C
but don’t go all the way to 400 (sorry Martin) simply because I use Green Sand when casting,
and for me there’s way more water in the sand than in the plaster, so I can’t see
the point – but I could be wrong, so I give you Martin’s sage advice and it’s up to
you whether you follow it or not. This process may seem a little cumbersome
but these plaster vents and feeders are a wonderful aid to metal casting and with all
the equipment now made and ready, they can quickly be produced and time and time again.
Try it and you’ll be surprised the difference it can make to your metal casting.
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’ve got any questions on this subject, drop me a line. Don’t forget
to check out my website and please subscribe if you haven’t already done so. Look out
for my other videos on my YouTube channel and send in any comments and video requests.
So that’s it for now guys, thanks for watching.