Horno electrico

A home built heat treatment furnace
WARNING NOTICE
Anyone following these instructions does so at there own risk. All electrical installations should be inspected and tested by a qualified electrician. You are working with high voltages and temperatures. The following instructions describe the design and construction of a simple but effective heat treatment furnace suitable for the knife maker.All measurements for the body of the furnace are given as a guide only, you are free to make yours as large as you want but making it smaller will cause problems in installing your elements. The casing measures ( 310 mm wide x 270 mm high x 465mm deep ) and the internal chamber measures ( 145 mm wide x 110 mm high x 380 mm deep ) this is suitable for most sizes of knife blade unless you’reintending making very large Bowie or camp/field type knives.

Furnace body
First of all you will need a minimum of 24 firebricks, these are the lightweight type 23 insulation bricks. Don’t be tempted to use any of the hard, heavy firebricks as these don’t insulate and you will not be able to carve the grooves for the elements. Next if you are building to the same size as I have, you will need to getsome 20 gauge stainless or mild steel sheet. I suggest that you have this cut by guillotine at your steel suppliers, as you need it to be perfectly square. 300mm wide x 460mm long x 2 off for top and bottom of case. 260mm wide x 460mm long x 2 off for each side. 300mm wide x 260mm high x 2 off for end and front door. You will then need approx 5.4 m of 25mm x 25mm x 3mm thick angle iron. Lots of5mm pop rivets!!!!

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I will not go into too much detail on how to build a box from angle and steel sheet as I am sure most of you are capable of working it out for yourself from the following photo’s. Needless to say, you are constructing a box on legs with dimensions as shown in paragraph 2. Just remember that you will have to beable to remove the top to install the elements and firebricks.

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Fit your firebricks in the case, working from the centre outwards and then cutting the bricks to fit. You should end up having to cut bricks about 35mm wide on either side. The brick are VERY easy to cut with an ordinary handsaw used for wood. I have also used a hacksawblade for trimming and carving the grooves.

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Once you have got to the stage as shown in the last photo, number the top layer of bricks so that you get them back in the same order.

Cutting element grooves and fitting elements
You will need to cut four equally spaced grooves down each side to hold your elements. These should be asnug fit around the element and be cut at a slight inwards angle as in this photo. This can be achieved by cutting two parallel cuts with the handsaw and the break out the middle. I then shaped the bottom of the groove with a hacksaw blade. Then finally to get a round

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bottom to the groove I took the element and rubbed it along thegroove to finish it of.

The elements MUST be made from Kanthal wire and are rated at 13 amp, 3.1KW 240V. If you use the same supplier as me you will need two elements wired in series. Each element is .270 in.O.D. x 34 in. long. Each element MUST be stretched to a minimum of 60 inches, and should not be stretched more than about 140 inches. They are designed to work at a maximum temperature of2300 oF. For more details on the elements please visit Budget Casting Supplies. www.budgetcastingsupply.com This is an American company that are really helpful and don’t mind dealing with small orders for hobby users. I ordered and paid for my elements and control by Paypal www.paypal.com They were very quick in getting the order out and Paul at BCS got back to my emails within hours!!! After...