20" Cloth PSA Sanding Discs, 5 PACK

A 20" disc sander is a production machine: a heavy cast platen, a large fixed or tilting table, and a rim that covers a lot of ground every revolution. The disc on it has to survive that rim speed with a heavy workpiece leaning on it, which is why we make these 20" cloth PSA sanding discs with resin-bonded aluminum oxide on X-weight poly-cotton cloth rather than paper. The cloth does not tear at the edge, the resin bond holds the grain through the heat, and the disc stays flat on the platen until the grit is used up.

They are bought for heavy-duty disc sanders in pattern shops, foundries, millwork and door plants, boat yards, sign shops and industrial arts programs. Wide end grain, laminated blanks, large mitres, aluminum pattern plates and steel plate edges are the everyday work. Each pack holds 5 discs of one grit, with 24 through 600 grit on the listing.

• X-weight poly-cotton cloth backing stays intact at the rim of a 20" platen
• Resin-bonded aluminum oxide for wood, laminates, aluminum, brass and mild steel at hand-feed pressure
• 24 to 600 grit on one listing: roughing, squaring, finishing, flattening
• PSA sticky-back mounting, no arbor hole, full platen coverage
• Pack of 5 matched to how long a 20" cloth disc lasts on a production machine
• Converted in Anaheim, California; free shipping on orders over $200

Which grit should you run on a 20" production disc sander?

The grain across all thirteen grits is aluminum oxide. Even on a large machine the work is fed by hand, so pressure sits where aluminum oxide does its best work: it cuts fast without needing the heavy load that makes zirconia or ceramic self-sharpen, and it wears gradually so the surface it leaves is predictable from the first part to the last. On a 20" disc the rim covers a lot of surface per pass, so err one grit finer than you would on a small machine if finish matters.

• 24 and 36 grit: roughing. Laminated pattern blanks, glued-up rings and thick bandsawn stock to the layout line, heavy end grain on timbers, skinning castings.
• 40 and 60 grit: heavy squaring and shaping. Wide crosscut ends, large radii on boat and millwork parts, dressing aluminum pattern plates and rough plate edges.
• 80 and 100 grit: the production disc. Squaring and fitting on door and panel work, truing templates and core boxes. Most 20" machines carry 80 grit.
• 120 and 150 grit: refining pattern surfaces before filler, cleaning up end grain that will show, easing edges.
• 180 and 220 grit: finish-ready surfaces on the machine, small parts, the last pass on a pattern before sealer.
• 320, 400 and 600 grit: deburring and polishing aluminum and brass, flattening plates and fixtures across a wide platen, fine work on dense hardwoods.

A three-grit stock for a 20" machine in a pattern shop is 36, 80 and 150; in a door or millwork plant, 60, 100 and 180.

Grit guide for a 20" disc sander

What machines take a 20" PSA disc?

• 20" heavy-duty floor disc sanders with a cast-iron platen and large table, the production disc sander found in pattern shops, foundries, door plants and industrial arts programs.
• Pattern makers' disc sanders and combination pattern-shop machines whose disc measures 20" across the platen.
• Stationary platen disc sanders in boat yards, sign shops and millwork plants built around a 20" adhesive disc.
• The old page also listed portable disc sanders and random orbital sanders. A 20" disc is a stationary-machine size only; hand-held tools take 5" or 6" discs on a back-up pad.

These are PSA discs with no arbor hole, applied to a bare, clean metal platen. Hook-and-loop faces must be removed or covered with a PSA conversion pad. Match the disc to the platen exactly; a rim that overhangs is unsupported and will tear, and an undersized disc leaves exposed metal that marks the work. On a 20" disc the difference in speed between the centre and rim is large: the outer band cuts fast and hot, the centre cuts slowly, so choose where on the disc you work by how much material you need to remove.

How to get the most out of a 20" PSA disc

1. Strip the platen completely. Peel the spent disc while the platen is warm, then wipe the whole cast face with mineral spirits or denatured alcohol until it is bare. Across a 20" platen even a small adhesive ridge becomes a high spot that burns a ring on every part.
2. Two people make a 20" disc easy. Machine unplugged, one person holds the disc centred while the other peels the liner outward and presses the disc down in a spiral from the centre. Working alone, peel a hand's width of liner, tack the centre, then walk the liner out around the disc, pressing as you go.
3. Let the adhesive wet out. Give the disc a few minutes before roughing work so the bond builds on the metal.
4. Feed on the down-running side only. On a 20" disc the up-running side has enough energy to lift a large blank and throw it. Mark the down side on the guard so every operator uses it.
5. Choose your radius. Rough on the outer band where the disc is fastest; do fine and small-part work closer to the centre where it is slower and cooler.
6. Keep the work moving with moderate pressure. Leaning on the disc generates heat and loads the grain; sweeping the work along the face does the cutting.
7. Step grits one or two grades at a time. 36 → 60 → 100 → 150 → 220 keeps deep scratches from surfacing under paint or sealer.
8. Clean the disc with a crepe eraser when glue, pitch or paint loads the grain; a loaded aluminum oxide disc still has plenty of life once cleaned.
9. Run the dust hood. A 20" disc moves a large volume of dust; extraction keeps the disc cutting and the shop air clear.
10. Store spare discs flat in the pack, liners on, cool and out of sunlight.

Use it for / don't use it for

Use it for

• Roughing and truing laminated pattern blanks, core boxes and glued-up rings
• Squaring wide end grain on timbers, doors, panels and stair parts
• Shaping large radii on boat parts, signs, millwork and templates
• Dressing aluminum pattern plates, castings, brass and mild-steel plate
• Plywood, MDF and laminated edges in production
• Flattening wide plates and fixtures at 320–600 grit

Don't use it for

• Hook-and-loop platens without a PSA conversion pad
• Hand-held sanders of any kind
• Heavy grinding on stainless or hardened steel; use zirconia or ceramic belts
• Wet or coolant-fed work; these are dry-use discs
• Platens that are not 20"
• Re-sticking a disc once it has been peeled

Specifications

Frequently asked questions

Related products and guides

• All cloth-backed PSA sanding discs, 5" to 30"
• 16" Cloth PSA Sanding Discs, 5 pack
• 30" Cloth Backed Aluminum Oxide PSA Sanding Discs, 3 pack
• Belt Eraser for cleaning loaded discs and belts
• Custom sanding belts made to order in about 3 days