Sanding tools for woodwork and model building

Sanding is the step that decides how a finished piece looks, and it is the step most people rush. A model with a clean seam and a careless sanding job will look worse under paint than one where the seam was slightly proud and the surface was taken properly through the grits. Primer and stain are both merciless: they even out colour and they exaggerate texture.

The good news is that sanding is mostly a procedure, not a skill. Follow the order and the result comes out the same every time.

The grit ladder

Every abrasive is numbered by how coarse it is. Low numbers cut fast and leave deep scratches; high numbers cut slowly and leave fine ones. Sanding is the process of replacing coarse scratches with finer ones until they are too small to see.

4D stocks Excel sanding sticks in six grades, and they are the ladder:

The rule that matters more than any tool: do not skip more than one step. Going 80 to 400 does not save time. The 400 is too fine to remove an 80 scratch, so you polish the surface around the scratch and the mark shows up under paint exactly where you thought you had removed it.

Most model work never needs 80 at all. Start at 240 unless you are actively reshaping something.

Sanding sticks and belts

A sanding stick is a rigid handle with an abrasive belt over it. The rigidity is the point: wrapped paper follows every dip in the surface and rounds over the edges you are trying to keep sharp, where a stick takes material off flat and leaves a crisp edge.

When a belt wears out you replace the belt rather than the stick, and replacement belts come singly or as an assorted pack. The pack is usually the sensible buy: singles are sold in 80, 240, 320, 400 and 600, so the 120 step is only available in the assortment.

Needle files, for shapes an abrasive cannot follow

A flat stick is the wrong tool for a concave curve, a slot or a corner. Files cut a shape rather than a plane, and 4D stocks the four useful profiles singly:

• Round, for opening out holes and smoothing inside curves.
• Half-round, the most generally useful: flat on one face, curved on the other.
• Square, for cleaning out rectangular slots and inside corners.
• Three square, a triangle, for tight internal angles.

If you are not sure which you need, the 12-piece mini needle file set covers the range for less than buying three singly.

Files clog, particularly on plastic and soft wood. A clogged file stops cutting and starts burnishing, and the swarf packed into the teeth will score the work. Brush them out as you go.

Tight spaces

Corners, grooves and panel lines are where most finishes fail, because the tool cannot reach and the area gets left. Three things help: a narrow sanding stick rather than a wide one, a needle file for anything with a profile, and cutting the surface back with a chisel blade before you sand at all. Getting a surface close with a blade means the abrasive is tidying rather than removing, which is faster and far more controlled.

Before you paint

Finish at 400 for anything going under primer. Going finer is not better: a surface polished to 600 gives primer less to key into.

Between coats, a very light pass at 600 knocks back dust and brush texture. The aim is to dull the surface, not to remove the coat you just applied.

On bare wood that will be stained, sand along the grain and finish no finer than 240. A polished wood surface absorbs stain unevenly and comes out blotchy, which is the most common finishing complaint there is and is almost always caused by sanding too fine rather than by the stain.

Three things worth knowing

Let the abrasive do it. Pressure loads the grit, generates heat and, on plastic, melts a skin over the surface that no amount of further sanding will fix.

Change direction each grit. Work at a slight angle to the previous pass. When the old scratches disappear, that grit is finished, which gives you a way of knowing rather than guessing.

Look at it in one colour. Bare plastic hides scratches because the eye reads the shine, not the surface. A quick mist of primer, or even holding it under a single light source, shows what you actually have.

Where to start

For most model work: one sanding stick at 240, one at 400, an assorted belt pack, and a half-round needle file. That covers everything short of reshaping, and it is four items.