3. Refractory putty (muffle). Chamotte will be good for that purpose, it can be bought in construction market. 25 kg sack costs 5 $. Before application I diluted it with water and kneaded thoroughly until I got consistence of curds. It’s a good idea to add water 1-2 hours before; it will be easier to dilute it later.
4. You may use asbestos cloth as a heat-insulating material; it’s sold in any construction market. I used basket weave of 3 mm thickness. It’s carcinogen but it can’t be helped.
5. Small items. Ceramic insulators of beads type, they may be taken out of an old iron (at worst you may do without them), ceramic terminal block (Fechral winding is attached to it), and wires (it is desirable for them to be heat-resistant). You will also need working crucibles and clips for their safe carrying. If art castings or thermal treatment of steel are planned, you will need a heat controller. It’s easier to buy this device ready-made with digital indicator and fine setting. The cost of the device is near 75 – 115 $. I bought it in the market for 55 $ from a gnarly man with booze breath and a wart in the nose. The device is imported, works without failures. So the seller didn’t trick me.
The manufacture process is simple only at first sight. You’ll use foul language more than once until you come to the finish.
After the heater has been winded, it must be smeared with chamotte (5-7 mm) and covered with one layer of asbestos blanket. After the “sandwich” has become dry, put it into metal casing taking into consideration electrical safety code (put beads on the wires, heat-resistant wires, grounding, etc.) and putty it with clay. Bottom and sides of the casing must also be covered with one layer of asbestos. Do the flowing in several portions; let the device get dry. You should do this operation necessarily in several steps because clay contracts greatly after becoming dry. Dry each layer on radiator for several days. After final drying adjust contacting surfaces of the lid and furnace casing with sandpaper. Clearance must be minimal. I recommend you to drill an opening of 5-7 mm diameter in the lid for temperature detector or sight control. Undoubtedly, it’s better to embed temperature detector in the furnace body beforehand. My modding is not so beautiful because detector’s wire sticks out of the lid.
