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A BRASS MELT IN PROGRESS

Having always purchased my castings I came to the conclusion it was time to learn how to make my own. The furnace itself uses nothing more than a couple of fire bricks for the base and a lining of Kaowool which is a ceramic blanket. For the initial experimenting I used a stainless steel toothbrush holder which worked extremely well but only held around a kilo of brass which is roughly equivalent to a ROB ROY  cylinder.

ROB ROY CYLINDER AND SMOKE BOX RING

Right, first I had to make a flask which is basically two simple wooden boxes called the cope and a drag (top and bottom) parts. You will notice I included some locking catches on the side in addition to the plastic locating blocks.This is to stop the possibility of the cope lifting when the metal is being poured in and ruining the job. The picture shows the drag with the core in place ready for the cope.

RESEARCH!

Next, a little research, and we are ready to make some molding sand. I used Bentonite which is a clay mixed with silver sand (Play sand) which is actually wind blown sand and doesn't contain any shell. I know brass is too soft for the cylinders but it is more than adequate for other castings like doors etc as shown below together with its pattern.

                                                                          FIRST EFFORTS

ROB ROY SMOKE BOX DOOR

ROB ROY CYLINDERS GUNMETAL

The cylinders did suffer from some shrinkage problems so in order to minimize this and to reduce the amount of metal required I looked at adding a core to the pattern. These cores are made of a mixture of silver sand and sodium silicate or water glass (Ebay). First dry the sand in the oven, place in a food bag and add a couple of teaspoons of the silicate. Next pack a suitable mold, in my case I found a plastic tube which I cut along one side so I could open it to extract the completed core. Lastly place in a bag and fill with a squirt of CO2 (fire extinguisher) Note: do not hold the nozzle unless you want frost bite! If you leave for several minutes viola! a nice hard core ready to use. The core can be seen in place in a previous picture.

SECOND ATTEMPT

In order to improve the surface finish I did have to play around with the amount of Bentonite and the dampness of the sand. Too damp and the sand holds together well but it reduces the permeability which is required for gasses to exit. Too dry and you risk sand inclusions as the loose sand is washed into the cavity.

ROB ROY SMOKE BOX RING

15th Feb 2015 - With the success of these parts I thought i would have a go at the cylinder castings for Britannia so onto the pattern making. It took a little head scratching but think I have worked it out. It will have two cores the split line running through the middle and finishing with a coat of varnish.

BRITANNIA 3.5" CYLINDER CASTING

Ok, so now it's time to get serious, so i purchased one of these....it's a salamander A3 size crucible which will hold around 3.7 Kg of brass. I also made some lifting tongues and obtained some borax to use as a flux.

I also purchased some Delft clay which is much finer so it is very good detailed work. It's main use is for jewelry making and seemed just the job for making a door ring for Minnie.

VOILA