TIN SMITHY & Sheet metal

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TIN SMITHY

Introduction :

Many engineering and house articles such as boxes, cans, funnels, ducts etc. are made from a flat sheet of metal. The process being known as tin smithy. For this the development of the article is first drawn on the sheet metal, then cut and folded, to form the required shape of the article. Allowance should be given in the drawing stage for folding and bending. This allowance depends upon the radius of the bend and thickness of the sheet metal.

Sheet Metal Materials :
A variety of metals are used in a sheet metal shop such as galvanized Iron, black, Iron, tin, Stainless Steel, copper and Aluminium.
Hand Tools :

The common hand tools used in sheet metal work are steel, try square, Wire gauge, Scriber, Ball peen hammer, Nylon Mallet, Snips Divider, Stakes, Cutting plier and Soldering Iron. Here, the details of tools that are being equipped by our workshop purpose only are presented.
Wire Gauge: The thickness of sheet is referred in numbers known as standard wire gauge (SWG). The gaps in the circumference of the gauge are used to check the gauge number.
Steel Rule : It is a strip of steel with graduations on its edges. It is used for measuring and setting out dimensions.
Scriber : A scriber is a slender steel tool, used to scribe or mark lines on sheet metal.
Snips : Hand shears or snips are used to cut sheet metal.
Straight Snips: These are having straight blades and are used for cutting along straight lines and fortrimming edges.

Curved Snips:These are having curved blades and are used for cutting circles and irregular shapes.

Divider: It consists of two pointed legs. The points are hardened and tempered to prevent wear. It is used for transferring the sizes and scribing curves or circles.
Bench vice: It is generally used for holding and bending the work piece.
Hammers: Light weight hammers and mallets are used in sheet metal work.
Ball Peen Hammer: It has a cylindrical, slightly curved face and a ball head. It is a general purpose hammer used mostly for riveting in sheet metal work.
Cross Peen Hammer: It has a tapered peen end and is perpendicular to the handle. Because of this, it can reach awkward corners.
Straight Peen Hammer: It has the peen end similar to the cross peen, but it is positioned parallel to the handle which can be used conveniently for certain operations of folding.
Cutting Plier: Used for holding, cutting and bending works.
Nylon Mallet: It is used for bending and folding work. It is light in weight, covers more area and do not damage the surface area.
Stakes: Stakes are made of steel and forged in a variety of shapes and sizes. These are used as supporting tool and to form, seam, bend or rivet sheet metal objects.
Anvil: Anvil provides the necessary support during hammering. It is also useful for operations such as bending. Its body is generally made of mild steel and a strip of high carbon steel about 20 mm thick is welded on top to provide hard face.
Sheet Metal Joints :
Various types of joints are used in sheet metal work, to suit the varying requirement. Some commonly used sheet metal joints and folded edges are shown in the figure. These are self-secured joints, formed by joining together two pieces of GI sheet metal and using the metal itself to form the joint.
Sheet Metal Layout :
The shapes of most articles made with sheet metal are in few geometrical forms. All these forms are made from flat sheet; therefore the first requirement is developing the lines, which forms the pattern. The development or stretch out of a job is called pattern and developing lines which forms a pattern is layout. It may be drawn on paper first and then transferred in the sheet or it may latyout directly on sheet metal. When a pattern is made repeatedly, it is generally made of metal and referred to as a template.

Insturctions:

1. Draw the development of object to be prepared with true dimensions only.
2. Use curved snip for trimming along inside curves.
3. Always provide folding (Hem) for top edges of the object to avoid sharp edges and to stiffen the sheet.
4. Ground properly the exposed metal parts of electrically heated soldering iron.
5. For good soldering the metals to be joined must free from dirt, grease and oxide.
6. Do not pull (or) peel the cut portion by hand while cutting with snip.
7. Do not bend the sheet with hand, always use nylon mallet with proper support.

Safetry Precautions :

1. Use hand leather gloves while handling heavy sheets.
2. Avoid feeling the cut portion by hand while cutting with snip.
3. Do not let sheet metal slip through the hands.
4. Never carry tools in pockets.

Exercise:
1. Plain pipe
2. Rectangular tray
3. Triangular tray
4. Funnel