Types of Chisel and Their Uses
Your first set of chisels should be of the bevel-edge type. They will do most chiselling jobs and have the advantage of being able to `undercut’ — get into tight corners — because of their tapered edges. Buy four to start with, say 6, 12, 18 and 25 mm (1/4, 1/2, 3/4 and 1 in).
Firmer chisels, which have blades of rectangular cross-section, are stronger and so better for heavier work such as fence-building and large frame construction.
The paring chisel can be of either blade pattern. Its blade is for paring out long housings, as on bookcases and stairs.
The mortise chisel is the stoutest of all, being designed to withstand the continual striking with a mallet to chop mortises.
When you buy any of these chisels, check that the blades are of the size stated (they often vary slightly). Note that chisel backs are flat in width only, and slightly `arched’ in length.
Chisels are never sharp when first bought, and the first thing to do with a new chisel is to hone the back flat for at least 35 mm (1-1/2 in) back from the cutting edge. The flatness shows up as a bright smooth area; and it must extend over the total width of the blade and right up to the cutting edge, otherwise the blade will never become sharp. This operation may take about 15 minutes; after completing it.
Gouges are of two types: the firmer with its bevel on the back, and the far more useful scribing type with the bevel on the inside face.
Chisels are mainly used for paring, joint cutting or for cutting out small areas of wood to receive hinges or other fittings.
Always use a chisel with or across the grain. Cutting against the grain usually splits the timber or causes the chisel to run off the intended line.
When driving a chisel into wood, as in cutting a mortise or removing the waste from a dovetail joint, always cut well within the waste area first, gradually working up to the marking-out lines for the final cut. If you start a cut on the line, the chisel will overshoot it as you drive it in. Make final cuts with the wedge of the chisel facing the waste area.
When mortises have to be cut near the end of a piece of wood, as with a table leg, the wedge action of the chisel tends to break off the wood at the end. To prevent this, leave some waste at the end of the wood, cut the mortise, and then trim the wood to size.
When cleaning out undercuts, such as a dovetail section, a square-edged firmer chisel will not reach right into the corners — use a bevel-edge chisel, which is specially made for the purpose.
Chopping out the waste from a dovetail joint calls for a narrow chisel to remove all but the last 1.5 mm (116 in) of the waste in front of the marking-out line. This last cut is made on the line with a chisel matching the width of the final cut as closely as possible. Drive the chisel in squarely.
Use a firmer gouge to cut shallow indents and curved grooves, and a scribing gouge to trim curves to match a mating surface.
When using a firmer gouge, work from each end alternately towards the middle until you reach the required depth.
The sort of job a scribing gouge is used for is fitting a rail to a round leg on a chair or table.
Only buy gouges as the need arises — the firmer gouge is the least used of all the chisel family. Note that gouges are always graded on the width of the blade, never on the radius of the cut.
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