How do I use a belt sander without gouging the wood?

Safety

What you'll need

• Belt sander and belts, 60–120 grit
• Clamps or bench stops
• Dust extraction or the collection bag
• Eye, ear and respiratory protection
• Random orbital sander for finishing

Step by step

1. Decide whether it is the right tool.A belt sander is for removing a lot of material: levelling a glued-up panel, taking paint off a door, flattening a worktop joint, dressing a fitted edge. For anything where finish matters more than removal, use a random orbital sander instead.
2. Clamp the work — always.The belt drives the workpiece forwards with real force. Anything not clamped or held against a bench stop will be launched. Two bench stops screwed to the bench are the traditional and best answer, because they leave the whole surface accessible.
3. Fit the belt the right way round.Belts have a direction arrow printed inside. Fitted backwards, the joint's overlap catches on every pass and the belt fails. Check the tracking too — the belt should run centred, adjusted with the small tracking knob, with the sander running free before it meets the work.
4. Start the machine before it touches the timber.Bringing it up to speed against the work digs a hollow at the start point. Start it in the air, then lower it flat onto the surface while it is already moving forwards.
5. Keep it flat and keep it moving.The whole platen must stay in contact. Tipping it onto the front or back roller concentrates the cut into a narrow band and gouges instantly. Move steadily in overlapping passes and never pause with the belt running on the surface.
6. Do not press.The machine's own weight is the correct pressure. Leaning on it slows the belt, generates heat, clogs the abrasive and cuts unevenly, and it makes the sander far harder to control.
7. Work diagonally first on a panel, then along the grain.For levelling, make passes at roughly 45 degrees across the surface in both directions to take the high spots down evenly, then finish with passes along the grain to remove the diagonal scratches. Working only along the grain from the start tends to follow the existing hollows rather than removing them.
8. Take the pressure off before lifting away.Ease the sander off the end of the work while still moving, or lift the front slightly and then take it away. Lifting straight up from a stationary position digs a dish.
9. Check constantly.Stop, wipe the dust off and look along the surface in a raking light after every couple of minutes. A belt sander removes enough material in ten seconds to spoil a piece, and the damage is invisible under dust.
10. Change belts before they stop cutting.A worn belt polishes and heats rather than cuts, which tempts more pressure. Belts are consumables — change them as soon as the cut rate drops noticeably.
11. Finish with a different sander.Even at a fine grit, a belt sander leaves straight-line scratches. Follow with a random orbital sander through the grits, or hand sand along the grain, before any finish goes on.

Tips

• A belt sander clamped upside down in a vice becomes a small bench sander for shaping small parts — a genuinely useful trick, with a guard arrangement and never with the trigger locked on unattended.
• Sanding a painted surface produces dust from the paint. On anything painted before the 1990s, treat it as potentially lead-containing: do not dry sand, and get the coating tested if you are unsure.
• The dust bag on most belt sanders is nearly useless. Connect a vacuum extractor if the machine will take one.
• Belt sanders remove far more than people expect on softwood. Practise on scrap before taking one to anything visible.

If it doesn't work