Lost Wax Casting Tutorial

Welding on the sprews

images and writing by Jake Powning 2007

Here are the tools I use for welding on the sprews and preparing the

waxes for casting. Sprews of square soft red wax and round blue wax wire,

the rubber sprew caps for holding the waxes while I make the molds and the

steel molds. Also, a square razor knife for cutting the sprews

and a small dentist tool for paring away any excess wax,

and a wax welder which is similar to a wood burner.

I start by cutting an appropriate length of square wax rod, and weld it to the

base of the model, once I have determined what the most efficient

path for the molten bronze will be.

I then cut and fit, a wax wire to bring bronze to any areas that won't easily

be reached by the main sprew or through the body of the model,

and weld in place.

It's important to imagine the molten metal flowing into the cavity created by the wax

and run small sprews to any high points. So I've welded on a second sprew

to the high point of the arch on the hand guard, just to be sure it fills.

Here are the two fittings with their sprews welded on, the blade collar only

requires one sprew as it is so simple.

The next step is to make sure the model fits in the mold,

and then attach it to the rubber mold cap.

I have attached this one with potter's clay.

On the blade collar the mold cap has a rubber sprew cap with a hole in it so I stick the sprew

in the hole and weld it in place with melted wax.

Before casting I paint the wax models with an anti- bubble

solution which reduces the surface tension of the models

so that air bubbles won't stick to them and create little

spheres of bronze on the finished product.

I use a pre mixed professional casting investment called satin cast.

I wrap the molds in duct tape to keep the liquid investment

from spilling out and tape a plastic collar on so

the investment won't overflow when I put it in the vacuum chamber.

For this investment I use three cups of water,

and 1700 grams of investment powder.

I set the timer for three and a half minutes to mix the investment

before I vacuum it to get rid of air bubbles.

I carefully pour the investment powder into the water, this process

is a little like making gravy, you don't want lumps.

I wear a face mask when I'm working with the investment powder.

It is composed largely of very fine silica powder

which if you breathe enough of it, will give you accute cronic silicosis.

Next I mix it with my hand and get any lumps out , bringing it to a nice creamy consistency.

I place the liquid investment inside a vacuum bell for 60 seconds,

this gets rid of the air bubbles in the solution.

Then I pour the investment in the mold with the wax model secured in it

until it is almost full,

leaving room for the investment to bubble, when I am removing the air in the vacuum chamber.

I place the mold in the vacuum bell for 90 second,

and then top it up with the last of the investment and let it set for at least two hours.

Burnout

Once the investment is thoroughly set it is time

to melt the wax out of the molds and heat them. This is done to

harden the investment, remove any moisture from the molds

and when casting have the molds at a heat that doesn't cool

the bronze too quickly, to insure that the spaces

left by the wax fill properly.

I raise the molds on fire bricks, so that the wax can flow

out the bottom with out hindrance.

Once I have closed the kiln I set the burn out cycle on a digital kiln controller.

2hrs to 300F

4hrs to 700F

6hrs to 900F

8hrs to 1350F

12hrs to 900F

hold at 900F

Go to the next page to see the casting process