Sanding and polishing acrylic: edges and scratches

Sawn or milled edges carry scratches that show through the whole part. Level the edge with P240 on a hand block, always lengthways and with the block flat on the edge – that keeps it straight and stops it rounding over. It almost never needs to be coarser than P240; scratches from P120 cost you three extra steps later.

Then P400 and P600, each time until the scratches from the previous step have gone. If you colour the edge with a felt-tip pen between steps, you’ll see at once where old scratches remain.

From P800, sand wet: water with a drop of washing-up liquid cools, rinses away the swarf and stops the grit from clogging. P800, P1000, P1500, P2000 – each step at right angles to the previous one, so you can see when the old scratch pattern has gone. Use the foam pad on flat surfaces and the sheet wrapped round a block on edges.

With a power sander, only at low speed and without pressure: acrylic heats up quickly, smears and develops stress cracks, especially around drilled holes.

After P2000 the surface is satin matt. It only becomes clear with polishing compound for plastics – by hand or with a soft polishing sponge at low speed. Light scratches on otherwise intact acrylic often come out with just P1500 to P2000 and polish; treat deep scratches like an edge and start at P400.