3"x 21″ Cork Sanding Belt – 8 Pack | For Premium Glass Fabrication Finishing

A 3 x 21 portable belt sander is the most common belt sander in North America, and with a silicon carbide belt it is a perfectly good glass and stone edger. What it cannot do with silicon carbide is polish. This ungritted cork belt is the missing last step: charged with cerium oxide slurry, it takes the 400 to 800 grit matte left by the silicon carbide belt to a clear polish on the same Makita 9903, DeWalt DW433 or Bosch 1274DVS class sander.

We convert these belts in Anaheim, California from natural cork bonded to a cloth backing and pack them eight to a box. Small glass shops without a floor-standing wet belt sander, stained glass and art glass studios, stone fabricators finishing an edge in place, and anyone polishing a glass table top or shelf edge with a hand-held sander buy them.

• Ungritted natural cork on cloth: a carrier for cerium oxide or pumice, not an abrasive
• 3 x 21 size for Makita 9903, DeWalt DW433 and DWP352VS, Bosch 1274DVS and other 3 x 21 sanders
• Follows the 3 x 21 silicon carbide belt on the same sander after 400–800 grit
• Runs damp with slurry; no water feed needed on a portable sander
• Turns a small shop's portable sander into a complete glass edging and polishing setup
• Eight belts per pack; converted in Anaheim, California

Why does polishing glass need a cork belt rather than a finer grit?

Every coated belt, however fine, cuts scratches. On glass an 800 grit silicon carbide belt still leaves a uniform grey matte that you can see and feel. To get from that matte to a clear edge you need loose polishing compound and a soft, firm carrier to hold it against the glass, and ungritted cork is that carrier. It has no grain of its own, so it cannot scratch, and its pores hold slurry the way a felt wheel does on a polishing lathe.

Charged with cerium oxide, the cork belt removes the fine matte and leaves a clear, polished edge. Charged with pumice, it gives a quicker, cheaper bright pre-polish that is often enough on an edge that will be framed. Run with no compound at all it simply warms the glass. The same belt polishes granite, quartz, solid surface and acrylic edges after a 400 grit pass, and knife makers charge cork belts with a green stainless compound to pre-polish bevels after 600 to 800 grit.

Which compound should you use on a 3 x 21 cork belt?

• Cerium oxide: the compound for a clear, optical polish on glass and mirror edges. Mix with water to a thin cream. Fastest after 600 or 800 grit; workable after 400 with more time.
• Pumice: a coarser powder for a bright pre-polish after 400 grit, or as the first cork stage before a second belt with cerium.
• Fine polishing paste: for stone, quartz, solid surface and acrylic edges.
• Green stainless compound: for steel and knife bevel pre-polish on a 3 x 21 sander clamped in a stand.

Compound is sold separately. Use one belt per compound and write the compound on the inside of the belt. A single pumice grain carried onto a cerium belt will scratch every edge it touches afterwards.

Grit guide: getting the edge ready for cork

Cork removes the last scratch pattern and nothing deeper. On a portable sander every stage runs on the same machine with a quick belt change, so step through the grits.

Hold the polished edge to a light. If you see lines, the fault is in the grit before cork, not in the cork; go back one belt and repeat.

Which sanders take a 3 x 21 cork belt?

• Makita 9903, the 3 x 21 sander most glass shops run. Verified fit.
• DeWalt DW433 and DWP352VS. Verified fit.
• Bosch 1274DVS and the metric Bosch GBS 75 AE / PBS 75 A (75 x 533 mm, the same belt). Verified fit.
• Craftsman CMEW213, Black+Decker DS321, Bauer 57587, Metabo HPT SB8V2 and Triton TA1200BS. All verified 3 x 21 machines.
• Any other sander built for a 3 inch by 21 inch belt. A 3 x 18 or 3 x 24 machine will not tension it.

This belt is the polishing partner to our 3 x 21 silicon carbide glass belt and mounts the same way: release the tension lever, slide the belt on, check the inside for a direction arrow, re-tension, start the sander clear of the work and set tracking so the belt runs centred. Cork is thicker than a coated belt, so expect the lever to feel firmer and re-check tracking after the first minute. If your sander has variable speed, use the low end for cork.

How to charge and run a cork belt on a 3 x 21 sander

1. Finish on silicon carbide at 400 grit or finer, 600 or 800 for the fastest cerium polish. Rinse or wipe the edge so no grinding swarf reaches the cork.
2. Mix the slurry: cerium oxide or pumice and water to a thin cream in a squeeze bottle.
3. Charge the running belt with the sander held clear of the work at low speed. Apply slurry to the moving cork until the whole face is damp and evenly coated. Keep slurry off the motor vents.
4. Polish with light pressure. Start the sander before it touches the edge, keep it moving with the platen flat on the edge, and let the machine's weight do the work. Pressure heats glass and slows nothing but you.
5. Keep the cork damp, not wet. A portable sander has no water feed and the cork belt does not want one; flooding washes the compound off. Add a squeeze of slurry when the face dries and the cut slows. Never let the belt run dry with compound caked on it.
6. Check against a light and go back one grit if lines remain.
7. After the job, release the tension lever and store the belt flat or hanging. Do not fold a cork belt.

Use it for / don't use it for

Use it for

• Polishing glass table top, shelf, mirror and cabinet door edges with a portable sander
• Finishing bevels and edges on stained glass and art glass pieces
• Polishing installed glass on site where a floor machine cannot go
• Granite, quartz, solid-surface and acrylic edges after 400 grit
• Knife bevel pre-polish with green compound on a sander in a bench stand

Don't use it for

• Seaming, shaping or chip removal; that is the silicon carbide belt's job
• Anything coarser than a 400 grit scratch
• Running dry with no compound, or under running water
• 3 x 18 or 3 x 24 sanders

Specifications

Frequently asked questions

Related products and guides

• 3" x 21" Silicon Carbide Glass Fabrication Belts, 12 pack (grinding stages before cork)
• All glass fabrication abrasives (silicon carbide belts, cork belts and discs)
• 3" x 24" Cork Sanding Belt, 12 pack, for the Makita 9924DB
• 4" x 24" Cork Sanding Belt, 6 pack, for Makita 9403-class sanders
• Custom belt sizes, including cork, made to order in about 3 days