Quick answer: A metal finish number – #1 through #4, 2B, 2D – describes how a sheet was processed and how uniform its surface grain is. On a Timesaver or other wide belt sander, you produce the ground finishes: a #3 is a coarse unidirectional grain from a 36 → 60 → 80 → 120 grit sequence; a #4 brushed or satin finish is 120 zirconia → 180 aluminum oxide → a very fine surface conditioning belt. Use zirconia belts on steel and stainless, aluminum oxide on aluminum, keep the feed steady, and finish every pass in the same direction.
What "finishing" means for metal
Finishing is any process that changes the surface of a manufactured part to give it a specific property – flatness, a uniform grain, a level of reflectivity, corrosion resistance. Sheet and plate come from the mill with a designated finish, and fabricators use wide belt sanders to take them the rest of the way. The finish numbers below are the standard designations for stainless steel; the same grinding sequences apply to mild steel and aluminum.
Metal finish numbers
| Finish | How it's produced | Appearance |
|---|---|---|
| #0 | Hot rolled and annealed, scale left on | Dark, scaly mill surface |
| #1 | Hot rolled, annealed, scale removed | Dull, rough, non-reflective |
| #2D | Cold rolled, annealed, pickled – no scale | Uniform matte |
| #2B | #2D given a light final cold pass on polished rolls | Brighter than 2D, slight reflectivity – the most common mill finish |
| #2 (BA) | Bright annealed in a controlled atmosphere | Mirror-like, reflective |
| #3 | Ground with 36–120 grit abrasive in one direction | Shallow, relatively coarse, uniform line grain |
| #4 | Ground through 120–180 grit and finished with a fine non-woven belt | Brushed / satin / "architectural" finish – short, fine, parallel lines |
Removing scale: from #0 to #1
Hot-rolled plate arrives with a hard oxide scale. On a wide belt sander, take it off with a 40 or 60 grit belt – a 37" x 60", 37" x 75" or 52" x 75" zirconia belt on the common Timesaver widths. Zirconia is the right grain here for steel, stainless and aluminum alike: it self-sharpens, runs cooler than aluminum oxide and holds up to the scale. Keep the feed steady and the depth of cut light; scale is hard on belts and dwelling burns the sheet.
Producing a #3 finish
A #3 is a ground, unidirectional finish made with coarse abrasives from 36 to 120 grit. The typical sequence is 36 → 60 → 80 → 120, every pass in the same direction so the line grain is parallel. On steel and stainless, run zirconia belts through the sequence. On aluminum, switch to aluminum oxide – it cuts aluminum cleanly without loading and leaves a brighter line. Use a grease stick on the belt when sanding aluminum to stop it welding into the grain.
Producing a #4 brushed or satin finish
The #4 is the most popular finish on stainless and aluminum – the brushed look on appliances, elevator panels, restaurant equipment and architectural cladding. It's a three-step process:
- 120 grit zirconia belt – establishes the flat, uniform base grain and removes the #3 scratches or the 2B mill surface.
- 180 grit aluminum oxide belt – refines the grain to the fine line pattern.
- Blue very-fine surface conditioning belt – a non-woven belt that softens the scratch into the even, low-gloss satin that defines a #4, and blends out any belt marks.
Run all three steps in the same direction, at the same feed rate, with fresh belts. A #4 finish is judged by its uniformity, and every inconsistency – a worn belt, a change in pressure, a pass at a different angle – shows. On a multi-head Timesaver, set the heads up as 120 / 180 / surface conditioning and produce the finish in one pass.
Belt choices by metal
| Metal | Scale removal and #3 | #4 base | #4 refine | #4 finish |
|---|---|---|---|---|
| Stainless steel | Zirconia 40–120 | Zirconia 120 | Aluminum oxide 180 | Very fine surface conditioning |
| Mild steel | Zirconia 40–120 | Zirconia 120 | Aluminum oxide 180 | Very fine surface conditioning |
| Aluminum | Aluminum oxide 60–120 with grease stick | Aluminum oxide 120 | Aluminum oxide 180 | Very fine surface conditioning |
Tips for a consistent grain finish
- Belt speed. Stainless wants 2,500–3,500 SFPM; mild steel and aluminum 4,000–5,500. See belt speed formulas.
- Pressure. Light and even. Heavy pressure on the finishing heads heats the sheet, discolors stainless and leaves a wavy grain.
- Direction. Always with the length of the sheet, every head, every pass.
- Contact roller. A harder roller for the coarse heads, softer for the finishing head, so the surface conditioning belt can conform.
- Fresh belts. A dull 180 belt leaves a different scratch than a new one. Change belts on a schedule, not when the finish goes off.
- Protect the finish. Apply protective film to the panel as it leaves the machine; a #4 scratches easily in handling.
We stock wide belts in the common Timesaver sizes – 25" x 60", 37" x 60", 37" x 75", 43" x 75", 52" x 75" – in zirconia, aluminum oxide and surface conditioning, and make any other size in about three days. Browse wide sanding belts and surface conditioning belts.
