Polishing Drilled Holes
A properly drilled hole has a smooth semi-matte finish that can be brought to a high polish. A wood or metal rod approximately
1 ⁄ 8 i n c h s m a l l e r i n d i a m e t e r t h a n t h e d r i l l e d h o l e i s s p l i t t o a d e p t h
e q u a l t o t h e d e p t h o f t h e h o l e p l u s 1 ⁄ 2 i n c h a n d m o u n t e d i n a
drill press. If the inner surface of the hole is rough, steel wool or strips of emery cloth or sandpaper are wound around the rod and gripped in the slot. When the inner surface is smooth, a good grade of flannel is wound around the rod and the compounds for buffing are applied. Poor grades of flannel may throw lint and require further cleaning.
In many installations, the edges of Plexiglas® acrylic sheet are completely hidden in a mounting frame or channel and smooth edges, free of chips and major irregularities, are entirely satisfactory. Sometimes good machine-finished edges are used as a decorative element in the design of a part made of Plexiglas® acrylic sheet. Well-polished edges, however, may be required for household accessories, jewelry, and other decorative items.
Saw marks can be removed from the edges of Plexiglas® acrylic sheet by scraping with a hard steel or Carboloy scraper square-ground to a straight, smooth edge. After scraping, the edges should be sanded on a wet belt sander with 320 grit then 400 grit sandpaper.
A fast method to polish Plexiglas® acrylic sheet is to make buffs
o f l a y e r s o f m e d i u m d e n s i t y 1 0 0 p e r c e n t w o o l f e l t a b o u t 3 ⁄ 1 6 t o 1 ⁄ 4
inch thick. The felt should have a specific gravity of about 0.27. The wheels should be 10 to 12 inches in diameter and should be held between hard faceplates about three inches smaller in diameter than the buff. The wheels should be run at a speed of 3,000-4,500 SFPM.
The edges are buffed on a felt wheel charged with abrasive and tallow. The final polish is given to the edges with a soft cotton buff. Felt wheels should not be used on large flat areas since there is a tendency to burn and distort the sheet.
Whenever possible, a number of Plexiglas® acrylic sheet parts should be locked together in a jig leaving only the edges exposed, so that the edges may be planed, sanded, and polished simultaneously. This technique is faster and gives better results without rounding the edges. Lapidary wheels surfaced with high-density felt may also be used for polishing flat surfaces.
To prevent heat buildup, the sheet may be buffed with a paste or liquid wax with an abrasive.
Flame polishing is a fast, economical method of edge polishing that is preferred by some fabricators, but it cannot be fully recommended for use on Plexiglas® acrylic sheet, because of its tendency to cause crazing – which is often not apparent until sometime after the article has left the fabricator’s shop. This technique is never recommended if other fabrication steps, such as cementing, forming or painting, are planned after the polishing step. Contact Altuglas International if additional information is needed.