Finishing Tools

Finishing is the stage where the work stops being nearly right and starts being right. Every tool here removes a small amount of material, and the questions are about how much, from what, and in what order.

Planes

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A plane's length is what makes it accurate. A long sole bridges the hollows and only cuts the high spots, so a jointer plane straightens an edge that a short plane would simply follow. That is why the longest plane is used for the straightest work, and it is the question the topic asks.

Depth of cut is adjustable, and a plane that is set too deep tears rather than shaves. A plane cuts with the grain: planing against it lifts and tears the fibers, which is the same grain reasoning as the saw lesson.

A block plane is the one for end grain, because its blade is set at a lower angle and is usually bedded bevel up, which suits cutting fibers off square.

Files and rasps

Files are named by cut and by shape, and both come up. Shapes include flat, half round, round (a rat-tail), square, triangular and mill. A round file is the answer for enlarging or smoothing a hole; a triangular file suits an interior corner.

A file cuts on the push stroke only. Dragging it back across the work dulls the teeth, so it is lifted on the return - which is the practice question here.

A file must have a handle. The pointed tang on a bare file will go into your palm if the file catches, and that is a safety item the subtest asks about.

A file card is the brush for clearing chips from the teeth. A loaded file stops cutting and starts scratching.

A rasp is the coarse wood tool. Its teeth are individual raised points rather than rows, which removes wood quickly and leaves a surface that then needs a file or abrasive.

Files are also graded by coarseness. From coarse to fine: bastard, second cut, smooth. A bastard file is the everyday, fairly coarse grade for removing metal quickly; a smooth file is for the finishing passes.

Abrasives

Grit numbering is the count of abrasive particles per unit area, so more particles means smaller ones, which means a finer finish. The number goes up as the abrasive gets finer, which is backward from the way most numbers behave and is precisely why it is asked.

Work coarse to fine, in order. Each grade removes the scratches the one before it left, and jumping from 60 straight to 220 leaves the coarse scratches in place - they are simply polished, which is worse, because they only become obvious once the finish goes on.

Sanders and grinders

A bench grinder's tool rest should be close to the wheel, within about an eighth of an inch, so the work cannot be pulled down into the gap. Adjusting that gap is the maintenance question for this tool.

A grinding wheel generates a great deal of heat, and overheated steel loses its temper. Dipping the work in water frequently while sharpening is standard practice for that reason.

Eye protection at a grinder is not negotiable, and a face shield over safety glasses is better still. A wheel that has been dropped or cracked can come apart at speed.

Know it by sight

The common abrasive grits are aluminum oxide for wood and metal and silicon carbide, harder and sharper, for glass, stone, and wet sanding between coats.

What you can skip

Across the 59 questions on this topic in our bank:

• Sharpening. Whetstones, honing and stropping never appear.
• Specialty planes and scrapers. The spokeshave never appears and the card scraper once.
• Grit numbers to memorize. Know that a lower number is coarser; the questions ask the order, not a grit for each job.

Where people lose points

Thinking a higher grit number is coarser. Higher is finer.

Skipping grades in a sanding sequence. Each grade removes the last one's scratches.

Using a rasp on metal. It is a wood tool.

Dragging a file back across the work. It cuts on the push only.

Using a short plane to straighten a long edge. A long sole is what makes it straight.

Using a file without a handle. The tang is a spike.

Work one in under a minute

A workpiece has been shaped with 60 grit and the finish calls for 220. A worker moves straight from 60 to 220 to save time. What will the result be, and why?

The 60 grit scratches will still be there, and they will show up under the finish.

Each grade's job is to remove the scratches the previous grade left. 220 grit removes very little material - that is what makes it fine - so it cannot cut deep enough to reach the bottom of a 60 grit scratch.

What it does instead is polish the surface around those scratches, which makes them less visible on bare material and more visible once a finish is applied, because the finish fills and darkens them.

The correct sequence is 60, then 80 or 100, then 150, then 220, and it is faster in practice than the shortcut, because the shortcut ends in starting over.

Where this leads

The plane's blade and the file's teeth are wedges again, and the order rule here is the same discipline the safety lesson asks for.