Short answer: To polish an acrylic edge, scrape or sand off the saw marks, wet sand through 320, 400, 600, and 800 grit on a block, then buff with a plastic polishing compound (or by hand with Novus No. 3 then No. 2) until the haze is gone. Flame polishing with a hydrogen-oxygen torch is faster but locks stress into the edge, so sheet makers say to anneal afterward and never flame polish edges that will be glued. Laser-cut edges come off the machine already glossy.

Key facts

  • Grit sequence: wet sand 320, 400, 600, then 800 grit before polishing (Acrylite). Start at 180 to 240 only if the edge is rough.
  • Buffing: soft muslin or felt wheels about 8 to 14 in. across, run near 3,000 to 4,500 surface ft/min (Plexiglas), with a fast-cut compound, then a high-luster compound, then a clean wheel.
  • Flame polishing: hydrogen-oxygen torch, bluish, nearly invisible flame about 3 in. (75 mm) long (Acrylite). Adds high stress; anneal afterward.
  • Annealing: about 180 °F (80 °C), roughly 1 hour per mm of thickness with a 2-hour minimum, then slow cooling (Acrylite).
  • Don't polish edges that will be cemented. Polishing rounds corners and stresses the surface; machine those edges smooth instead.

Four ways to polish an acrylic edge

MethodResultGood forWatch out for
Sanding and hand polishClear, slightly soft cornersAny edge, by handTime; rounding edges
Buffing wheelGlossy, slightly roundedStraight and curved edgesHeat, burning, rounding
Flame polishingGlossy, fastEdges that won't be glued, painted, or cleaned with solventsBubbles, crazing later
Diamond polishingCrisp, square, very clearStraight edges on displays and thick partsNeeds a specialized machine

How do you sand and polish an acrylic edge by hand?

  1. Remove saw marks. Acrylite says a saw-cut edge has to be sanded, routed, or scraped before it can be polished. To scrape, clamp the part with the edge up, tilt a sharp, square-edged scraper (a cabinet scraper or the back of a utility blade) about 45°, and draw it along the edge with even pressure. Scraping keeps the edge flat and saves a lot of sanding.
  2. Sand on a block. If the edge is still rough, start at 180 to 240 grit; otherwise go straight to 320. Use wet-or-dry paper wrapped around a flat block and plenty of water, and sand along the length of the edge.
  3. Step through 400, 600, and 800 grit, wet. At each grit, sand only until the scratches from the previous grit are gone. For a near-glass edge without a buffer, keep going to 1,500 to 2,000 grit.
  4. Polish by hand. Novus No. 3 (heavy scratch remover) takes out the last sanding marks; Novus No. 2 (fine scratch remover) finishes the haze. Work in small circles on a soft cloth, then wipe clean with Novus No. 1 or plain water.

Tip: clamp a scrap of acrylic on each side of the edge you're sanding. The block rides on a wider surface and you won't round the corners. Trinseo recommends the same idea for production: lock several parts together in a jig so their edges are sanded and polished as one flat surface.

How do you buff an acrylic edge?

Once the edge is sanded to about 600 or 800 grit, a buffing wheel brings it up to a gloss quickly. Acrylite suggests soft bleached muslin wheels, 8 to 14 in. (200 to 300 mm) across, with bias-cut pleats. Trinseo's Plexiglas guide gives a wheel speed of 3,000 to 4,500 surface feet per minute; for a 10 in. wheel, that's roughly 1,150 to 1,700 rpm.

  1. Charge the wheel with a fast-cutting plastic compound and buff until the sanding marks are gone.
  2. Switch to a separate wheel with a high-luster compound for the final shine.
  3. Finish on a clean wheel with no compound to remove residue.

Use light pressure and keep the part moving. Acrylite warns that too much heat from buffing builds stress into the edge that can later craze. Buffing also rounds the corners slightly, which looks fine on signs but is wrong for glued joints.

How do you flame polish acrylic?

Flame polishing melts the very surface of the edge for an instant so it flows smooth. Acrylite specifies a hydrogen-oxygen torch with a bluish, nearly invisible flame about 3 in. (75 mm) long and narrow. Hobbyists use MAPP or propane torches, but those flames are cooler and dirtier, so the edge heats more deeply before it glosses.

  1. Sand or scrape the edge smooth first. Flame glosses scratches but doesn't remove them.
  2. Peel the masking back from the edge, or sandwich the part between scrap acrylic so the flame can't touch the faces.
  3. Draw the flame along the edge in one steady pass. Don't stop in one spot.
  4. If it's still hazy, let it cool fully, then make a second pass.
  5. Anneal the part afterward if you can.

The risks:

  • Bubbles. Too slow a pass boils the surface and leaves bubbles that only sanding removes.
  • Crazing later. Acrylite notes that flame polishing induces a high degree of stress. Trinseo goes further: it can't fully recommend flame polishing Plexiglas, because the crazing often shows up after the part has left the shop, and says never to flame polish before cementing, forming, or painting. Alcohol and ammonia cleaners trigger that crazing too (why acrylic cracks later).
  • Fire. Acrylic is combustible and burns vigorously. Work away from anything flammable.

Should you anneal after polishing?

For parts that will be glued, cleaned often, or kept for years, yes. Annealing is a long, gentle bake that relaxes the stress polishing leaves behind. Acrylite's schedule is 180 °F (80 °C) in a forced-air oven for about 1 hour per millimeter of thickness (2 hours minimum), then a slow cool, leaving the parts in until the oven is below 140 °F (60 °C). If only the surface was worked (polishing or machining, no cemented joints), Acrylite says 2 hours of heating and 2 of cooling is enough. Other makers' schedules differ by grade; Trinseo's for cast Plexiglas runs hotter and shorter. Anneal after all polishing is done.

Why do laser-cut edges already look polished?

A CO2 laser vaporizes acrylic, and the walls of the cut melt for an instant and set glossy, much like flame polishing. That's why laser-cut parts usually need no edge finishing. The trade-off is similar too: laser edges carry stress, and Trinseo lists laser-cut edges with flame-polished ones as surfaces where solvent cement shouldn't be flowed. See laser-cut vs router-cut edges.

What is diamond polishing?

Diamond polishing uses a machine with a spinning diamond-tipped cutter that takes a very fine final pass along a straight edge. The result is a crisp, square, mirror-clear edge made without the heat of a flame, which is why it's a favorite for display cases, thick blocks, and awards. It only works on straight edges.

Fixing scratches on the face

The same sequence works on scratched faces, but you have to sand a wider area to avoid a visible dip. Trinseo suggests starting with 600 grit and dropping to 400 only if needed. See how to remove scratches from acrylic.

Or let us finish the edges

We offer laser, machined (satin), flame-polished, diamond-polished, and sanded edges. See acrylic edge polishing, then pick the edge in the instant quote.

Questions

What grit sandpaper do you use to polish acrylic edges?

Acrylite's sequence is wet sanding with 320, 400, 600, and 800 grit, then buffing. Start at 180 to 240 only if the edge is rough or chipped, and go to 1,500 to 2,000 grit if you're finishing by hand instead of with a wheel.

Does toothpaste polish acrylic edges?

It's a mild abrasive and can take out very light haze after fine sanding, but it's slow and inconsistent. A plastic polish such as Novus No. 2 works better.

Can I polish acrylic edges with a heat gun?

Usually not well. A heat gun's air is too diffuse to melt just the surface, so it tends to warp or bubble the part before the edge glosses.

What torch is best for flame polishing acrylic?

Sheet makers specify a hydrogen-oxygen torch with a small, bluish, nearly invisible flame. MAPP gas works for occasional hobby use; plain propane often heats too slowly and warps or bubbles the edge.

How do I make a frosted edge instead?

Sand evenly with 180 to 320 grit and stop. That gives a uniform satin edge that hides small chips and looks clean on modern pieces.

Sources