I needed some lead balls for using in a homemade ball mill and they are too expensive to buy and I had some lead kicking around in the shed so I figured I would cast my own.
At this point it is worth noting that lead is poisonous so be careful.
you can cast pewter in the same method as I have shown for the lead.
Step 1: What You Will Need
some lead, I used roofing lead off cuts
plaster or other casting media
non-drying modelling clay
old tin can
biscuit tin or somewhere to put scrap molten lead
an old teaspoon
long handle pliers
1 x G clamps
a shallow muffin tin or somewhere to put excess molten lead
hacksaw or tin snips to cut off excess lead
old scissors for cutting lead
Step 2: Making a Mould
using my non-drying modelling clay I made a ball of roughly the right size, then made a rough cone which will form my sprue.
I cut it in half and lay one half on my desk.
Make a small ball and cut that in half and place the 2 halves on either side of the part to be cast, make them staggered, these will form our key for the mould making sure it will only fit together in the correct way and aligned correctly.
using the modelling clay build walls all the way round the part but make sure the bottom of the cone/sprue is butted up to one of the walls.
mix up your plaster to the consistency of thick cream, only mix up enough for this half of the mould, pour this in to the mould all the way to the top of the walls.
Agitate (shake gently) the mix to dispel any bubbles.
let your plaster harden then remove the walls and turn the mould over.
remove the small ball parts we used for the key, and then using a hobby knife carve off the edges of the key points so there's no overlap.
now place the other half of the part on top of the one in the plaster, line it up and push down lightly to make it stick.
now build walls again high enough so they come above the highest point of the part.
coat the plaster and the 2nd half of the part in a thin coat of petroleum jelly, this will act as a release agent and stop the plaster sticking to its self so we can separate the 2 halves.
now mix up some more plaster and pour it in to the 2nd half, agitate again and then wait for it to harden.
once its hard remove the walls and separate the mould, remove the clay from the mould.
now you can wait for a couple of days for the mould to dry out or you can cheat, pop the 2 halves on a baking tray separately, pop in a cold oven then put the oven on low and leave for a few hours to get the water out the moulds.
do not cast with wet / damp moulds, they will crack/crumble or explode.
Step 3: Prepare Your Lead
I'm using roofing lead off cuts so it's easy enough to cut up with some old scissors.
you need to make small pieces so you can gradually fill your crucible (tin can)
Step 4: The Melt
pop your can on the small ring of your hob on high heat, pop about 5 or 6 bits of lead in.
your can will smoke to start with as it burns off the coating inside the can, this will stop after a few minutes.
important note here, do not put too many pieces in at once you will freeze the melt, e.g. it will solidify and take a while to melt again.
slowly add up to 4 pieces at a time, waiting for each batch to melt before adding the next, you can check if they are melted by poking the pieces you have put in.
don't put too much lead in your crucible otherwise you may not be able to pick it up safely. only melt what you need maybe a little more to be sure you have enough.
once all your lead has melted, leave it for a few minutes to super heat, this will give you extra time for your pour.
using your spoon, bend it so you can get it in the crucible, hold it with the pliers and skim off the debris floating on the top this is known as dross. tap your spoon in the biscuit tin to get rid of the dross.
to pick up the crucible use the long pliers.
those who have done casting before might be tempted to put in salt to help as a flux, don't do this it produces too much gas, don't put anything in the metal its fine without it.
Step 5: The Pour
do your pour outside for safety.
hold your mould together using a clamp.
pick up your crucible and take it to your mould, put it down next to your mould and adjust your grip so you're ready to pour.
pour slowly in to your mould, it should be a steady trickle, too fast and the air inside will bubble and splash lead everywhere and create gas pockets.
make sure you fill your mould up to the top of the sprue, this is important as when the metal cools it will shrink this sprue will help feed the mould making sure you don't get dips or voids.
once you have filled the mould return the crucible to the hob and turn the heat down, you just want to keep it liquid, you can turn it back up when you want to add more lead.
wait for a few minutes for the lead to cool in the mould, you can then release the clamp and remove one half of the mould.
using the pliers grab hold of the sprue and wiggle the cast and it should release.
Step 6: Finishing
using a hacksaw or some tin snips cut off the sprue as close to the part as you can.
using a file clean up the edges and the cut where the sprue was.
you can pop the sprue you cut off back in to the crucible.
if you have finished casting pour the remaining lead in to the muffin pan to form an ingot which can be melted down the next time you want to cast something in lead.