Jeshua Lacock Presents Lost Shell Sand Casting for PLA 3D Printed Models

[3DTOPO]

okay. Yes now you mention it.
In the lost wax/pla process you heat the mould to melt the wax out before adding the metal.

That is correct as well.

So why are the tubes (can't remember what you called them) for the metal in and gasses out so large ?

The the pour tube is called a "Sprue". It is both tapered and oversized to help build up as much hydrostatic pressure as possible (also makes it easier to pour into). It also acts as a "Riser" that stays molten long enough to feed the metal as it shrinks as it cools which is called the "Suck".

And would this process also work with lead ? or does that not get hot enough to vapourise the pla ?

Let's see; it looks like lead doesn't boil until 3,180F. So you could get it plenty hot enough to work for the process. How much hotter it needs to be over the melting point of 621F would take some experimenting. I imagine if you got it up to around 1000-1200F that seems like is should be adequate.