THE FORGE

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The main sheet-metal tool is a set of tin snips. A set of three aircraft snips - one that cuts straight and others that cut right and left - costs less than $20 and makes snipping copper or aluminum a snap.

To cut steel of any thickness, you need power tools. I have a pneumatic shear and a nibbler that nips off little bites of steel as it goes. Each costs about $40 and one or the other goes through auto-body metal like soap. Air tools are covered below.

JOINING AND FASTENING

The bread and butter of the business of fastening is the rivet. A bewildering array are available in bulk to the trade, but not by the pound or piece in most hardware stores. You can buy round-headed soft-steel rivets, flat-headed copper rivets and burrs (washers) up to 11/2" long; and copper slating nails (those you can purchase in bulk, for about $3 to $5 per pound). Plus, you can get a variety of brass- and steel-threaded knifemaker's rivets at $1 to $3 a pair from blacksmiths' and farriers' supply houses (see Sources ).

Sheet-metal fastening has been made infinitely easier by the general availability of hand rivets and rivet guns You no longer have to get in back of a rust hole in a truck fender or a gutter to fasten a bolt or rivet to secure a patch. Working entirely from the outside, you drill or punch holes through both metal sheets to be fastened. Then the pop rivet is pushed through and the rivet gun is squeezed; it pulls on a wire mandrel that crushes the rivet, cinching it into a flat head tight against the inside of the patch. The mandrel pops off and you have a functioning rivet. A marvel!

Get a heavy-duty hand or air punch to make rivet holes. Drilling floppy sheet metal can be a task; a block of wood in back of the metal will allow you to make a dent to start the drill and give you something solid to push the drill hit against. But even this takes three or four hands, while a punch takes just one hand.

Blind or "pop` rivets are made of aluminum or common or stainless steel and come in 1/8" 1/4" and 3/8" grip (thickness of material riveted together) and in diameters of 1 1/16", 3/32", 1/8", 5/32" and 1/4" . In most stores (if they stock rivets at all), 1/8" diameter is all that is commonly available. The best selection of rivets and riveters is found in the JC Whitney auto parts catalog. Whitney also carries two kinds of threaded rivets: with these, you pop the rivet body into the back sheet; then, using the little screw bolt that threads into it, you can screw on a removable. Patch, hinges for access/inspection ports and much more. To make a thin steel or aluminum flashing box for any purpose other than heating water, draw a full-size paper pattern with sides and ends attached to the rectangular bottom. Make inch-wide tabs on each side of the ends. Lay the pattern over the steel and cut out with tin snips. Clamp sides and ends between two lengths of strap iron to make sharp bends. Bend sides and ends up and fasten bent-in tabs to sides through punched holes with pop rivets. Use a modern clear caulk/sealer to waterproof joints. Before bending. you can use clamped iron or wide-jawed flanging pliers to bend sharp edges into a narrow flange or lip to increase edge strength and prevent tin cuts.

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