Hi YouTube, my name’s Geoff and I’m the VegOilGuy.
I’m doing a lost foam casting experiment for you today.
But rather than using the green sand method which gives me consistently good results,
today I’ll be using dry sand and plaster.
I guess we can call this one a subscriber request, because I must have had a good few
people write to me saying, “Don’t bother with that green sand stuff,
use a thin coat of plaster,” and frankly I wanted to see if they were right.
So I prepared my foam in my usual way, which includes a partially hollow centre.
This time though, I attached some string to the screws in the gates, to enable me to hang
the pattern to drip dry.
I didn’t want to get all of the gates and especially the screws covered in plaster,
so I covered these with masking tape.
Not wanting to be too wasteful with the plaster of Paris, rather than make up a dip load,
I placed the foam pattern in a container and poured on a fairly watery mix.
I took a small brush and worked the plaster all over the pattern, making sure everywhere
got covered.
Then I thinned this out as best I could and hung the pattern to drip and dry.
This isn’t the best camerawork here, but you can tell that I’m using the brush to
thin the plaster from the bottom of the pattern – hence the drips.
I left this a good few days to dry out and even hung it outside on an unusually sunny
day, and this is the result.
The plaster is certainly nice and thin in places as the blue of the foam can be seen,
but in others it’s a little thick.
As I believe the principle of this technique involves a thin coating, I decided to have
a go at sanding away some of the thicker stuff.
The bottom was an obvious place to start, where all those drips had concentrated and
dried.
I rubbed this on some coarse sandpaper and tried to avoid cutting into the foam pattern.
As you can see, I came a little close, but I think I got away with it.
Next came the top and then within the spokes, and this required a little more care.
Now whilst I revealed the foam in places, I didn’t do too bad and I thinned the plaster
as much as I was able.
Notice also that I’ve removed the masking tape.
This actually came away better than I expected, and it reveals just enough of the gates for
me to use my plaster feeder and vent.
Here’s my box of dry sand.
Ideally you’re looking for fine but coarse sand and that sounds a bit contradictory,
but it’s basically small grains that have a rough texture.
This is block paving sand and seems to fit that bill nicely.
I’ve emptied this box leaving just 2 or 3 inches of sand at the bottom.
Then the pattern is placed inside.
Well actually it’s gently shook into place.
I’m agitating the pattern and forcing sand to flow all around it.
I’m trying to fully support the pattern and remove any voids.
Once it started to feel a little stiff, I vibrated the box just a little then added
more sand.
I poured slowly from quite a height, encouraging the sand to scatter as it landed.
I then added enough sand to just submerge the gates.
At that point I started to bang the box around a little and this is very important.
In industrial plants, vibration plates and even vacuums are used to persuade the sand
to fully enclose the pattern, and amazingly this banging really does work.
So don’t skimp on this stage.
The agitation shrunk the sand down enough to reveal the upper parts of the gates and
a dry brush eased away a little more.
From there I removed the screws and string.
Here’s the plaster vent and this fits neatly on the foam gate with a gentle push.
It has a paper cover at the moment to keep out any sand.
And here’s the plaster feeder.
If you’re wondering why there’s tape around the bottom of this, it’s actually broken.
I dropped and cracked it.
But that won’t stop it working.
The tape and sand will hold it together well and it will still contain the molten metal.
I also add a strip of tape around the top of the feeder, just in case I knock that.
I know what I’m like.
Sand is carefully trowelled in to avoid disturbing the feeder & vent and this flows nicely and
fills the voids.
But it’s not very secure just yet.
So I use the trowel to help pack the sand slightly, and more sand is added until I’m
roughly an inch from the top of my box.
The feeder is still a little loose.
The sand hasn’t bound around it properly yet.
So it’s time to vibrate the box again.
I’m hitting the outside of the box with a rubber mallet, again to vibrate the sand
into place.
This is sufficient to lower the sand level a little, so I add a some more.
More banging with the mallet was required.
Now the feeder and vent feel much more solid.
But me being me, I couldn’t resist just giving them a gentle tapping, just to make
sure.
Now it was pouring time and again my home made electric foundry was happily ticking
away at 760 degrees.
I removed the paper covers from the feeder and vent, then took the red hot crucible from
the foundry.
This pour fooled me.
Seeing the metal spout from the vent, I assumed the feeder was full.
But I was mistaken.
If you look more carefully you can actually see the metal is jumping from the vent as
if it’s trying to get out.
There’s a lot of gasses pushing that metal.
It’s not overflowing.
The metal is spurting out in globs.
Based on the evidence of this, I wasn’t expecting anything good.
It must have been very turbulent in there.
Roughly an hour later I decided to dig out the results.
Other than the where the metal had laid on surface, there was no sign of sand discolouration
– and we want to see sand discolouration.
So I excavated slowly, trying to take the dry sand away in thin layers.
But there was never really any sign of it, other than a little towards the very bottom.
When removing the work, I was actually quite surprised.
I was actually expecting much worse.
With the plaster and sand quickly removed, it doesn’t look too bad.
I’m feeling the edges here and there’s a fair bit of roughness.
It’s hard to see but easy to feel.
There was also a tiny amount of distortion, plus swollen and blistered surfaces.
There’s also a few small tears.
The centre hole was fairly circular – but not on both sides.
Still it sat nice and flat and when compared with a similar wheel I made using my green
sand technique, it was a good size match.
Side by side, the thin plaster work isn’t bad, but I think it doesn’t match the sharper
detail and crisper lines of the green sand example.
But you decide for yourself.
So I certainly won’t write-off the thin plaster method.
It seems to have merit.
Perhaps I didn’t get the thickness of the plaster right.
If you’re into using plaster coatings, drop me a line or post a comment.
I’d genuinely like to see how precisely I could cast with this method.
But for now, I think I’m going to be sticking to my green sand.
So 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.