Routing Plexiglas® Acrylic Sheet
Portable routers are used for trimming the edges of flat or formed parts, particularly when the part is too large or it is too awkward to use a band saw or stationary router.
Routers should have a minimum no-load spindle speed of 10,000 rpm – higher speeds are more desirable. Double,
s t r a i g h t - f l u t e d c u t t e r s 5 ⁄ 1 6 i n c h e s t o 1 ⁄ 2 i n c h i n d i a m e t e r w i l l p r o d u c e
the smoothest cut at this speed. Cutters should be kept sharp and should have a back clearance angle of approximately 10° and a positive rake angle up to 15°. Templates should be provided to guide the router. Machining Plexiglas® Acrylic Sheet (page 11) gives complete details for routing Plexiglas® acrylic sheet.
For Plexiglas® MC acrylic sheet, double or triple, straight, fluted
r o u t e r b i t s w i t h a m a x i m u m d i a m e t e r o f 3 ⁄ 4 i n c h e s , a b a c k l i p
clearance of 10°, and a positive rake angle of about 10° produce good edges. Two fluted edges are recommended. Steel router bits will produce an excellent initial cut, but carbide bits can give a comparable cut and will give many times longer life. The spindle speed required to produce a satisfactory edge is 10,000 to 20,000 rpm. A smooth, constant feed rate of 10 to 25 feet per minute is required to prevent localized heat buildup, which will cause smearing or gumming of the cut edge. Low-horsepower (1 hp) routers should not be used, since they may bind on the material, removing chunks rather than yielding a smooth edge. A v o i d u s i n g r o u t e r b i t s l e s s t h a n 5 ⁄ 1 6 i n c h e s i n d i a m e t e r b e c a u s smaller diameter bits tend to clog and break. Use a router setup design that will effectively remove router chips. e
Routers with computerized numerical control are favored by some fabricators involved with high-speed production operations.
Scribing and Breaking
Straight cuts in 0.236 inches or thinner pieces of Plexiglas® acrylic sheet can be made by scribing with a special Plexiglas® acrylic sheet cutting tool available at Authorized Plastics Products Distributors. Scribing is effective when the quantity of sheet to be cut is limited, for it requires very little capital outlay for tools. Neither thick sections nor patterned Plexiglas® acrylic sheet can be cut by this method, however. If the sheet is masked, it should first be scored using the tip of the tool and a metal straight edge as the guide. Then the hook point of the cutting tool is placed at the far edge of the material and drawn the full width while
applying firm pressure. This is repeated once for every 0.025 inches to 0.040 inches of sheet thickness.
T h e s c r i b e d l i n e i s t h e n p o s i t i o n e d f a c e u p o v e r a 3 ⁄ 4 - i n c h
diameter wood dowel running the length of the intended break. The sheet is held with one hand and downward pressure applied with the other hand on the short side of the break. The hands should be kept adjacent to one another and successively repositioned about 2 inches behind the break as it progresses along the scribed line. The practical minimum cutoff width for
s c r i b i n g a n d b r e a k i n g i s 1 1 ⁄ 2 i n c h e s .
Scraping Edges of Plexiglas® Acrylic Sheet
After cutting Plexiglas® acrylic sheet, it is often desirable to scrape the edges. Scraping serves two purposes: it removes any nicks or burrs that may form a notch to weaken the material, and it improves the appearance of the edge by removing cutting marks. Dubbing both edges at the same time may be done by grinding a V-notch into the scraper.
A suitable scraping tool may be made from a piece of power-hacksaw blade or tool steel with one edge ground to a sharp 90° edge.
The Plexiglas® acrylic sheet part should be held firmly in a vise or holding fixture. Scraping can be accomplished by pushing or drawing of the tool, whichever is more comfortable. Firm, steady pressure should be used throughout the scraping operation. Care must be taken to keep the scraped edge square.