Routing and Shaping
Woodworking shapers (also called table routers) and overhead or portable routers are used in edge-finishing operations and for cutting flat or formed Plexiglas® acrylic sheet parts to size. For edging small parts, the table router is convenient; portable routers are useful whenever the acrylic part is too large or awkward to bring to the machine.
Routers should have a minimum no-load spindle speed of 10,000 rpm. Higher speeds of 20,000 to 25,000 rpm are desirable and should be used when possible. At slower spindle speeds, cutters should have more flutes or larger diameters to produce necessary surface speeds. Double or triple straight-fluted cutters
5 ⁄ 1 6 t o 1 ⁄ 2 i n c h e s i n d i a m e t e r w i l l p r o d u c e g o o d c u t s . S m a l l e r
diameter cutters should be used with care. If cutters larger than
1 ⁄ 2 i n c h i n d i a m e t e r a r e u s e d , t h e m a t e r i a l s h o u l d b e m a c h i n e - f e d
rather than hand-fed to overcome chatter. For safety, cutter shanks should be as large as cutters in diameter. Single-fluted cutters should not be used under any circumstances.
When machining thick sections of Plexiglas® acrylic sheet, better-quality edges may be produced by using spiral-fluted cutters. Spiral-fluted cutters always have a cutting edge in contact with the material and chatter less than straight-fluted cutters. This is done best when the material is held down securely.
Carbide-tipped cutters should be used whenever possible since they stay sharp longer than high-speed steel cutters. All cutters should be kept sharp and should have a back clearance of about 10° and a positive rake angle of up to 15°.
The most common operations performed with routers are deflanging and flange trimming. These cuts are illustrated in Figure 3 (shown at right). Such cuts may be made with router cutters or with veneer saw blades attached to portable or table routers by suitable arbors. Typical deflanging cuts commonly made on formed Plexiglas® acrylic sheet are shown in Figure 4A ( page 13).
When deflanging cuts must be made to close tolerances, fixtures should be used to support the Plexiglas® acrylic sheet and index the cut. Female fixtures are used for close tolerance referred to the convex side of a formed part; male fixtures, to the concave side as indicated in Figure 4B (page 13). The material should be clamped to the fixture. In trimming close tolerance work, the part should not be supported by its flange.
In contrast to deflanging where the entire flange is removed, flange trimming is merely reduction of the size of the flange. Table and panel saws can be used for flange trimming and will produce a good-quality edge. For high accuracy trimming with a table saw, place the part on a lightweight male shape with runners to fit the saw table grooves. Another method is to install a gauging device on the saw fence so that the flange is trimmed by indexing from the outer surface of the return of the part. These methods are illustrated in Figures 5A and 5B (page 13).
Portable routers or table shapers equipped with woodworking router bits are also commonly used in this operation. Depending on the equipment used, a template may or may not be necessary.
Figure 6 (page 14) shows deflanging cuts made with a table router with and without a template. The lower illustration shows a special router cutter tipped with a ball bearing pilot. This cutter is useful in trimming cemented assemblies. The pilot is the same diameter as the cutter and rides the guiding surface of one part of the assembly as the cutter trims the other.
Another cutting operation using a portable router is shown in Figure 7 (page 14). A template is cut to size and held to a work table, along with the Plexiglas® acrylic sheet to be cut, by means of air cylinder clamps mounted overhead. The router is fitted with a bushing that enables it to follow the template, cutting only the sheet.
Common Router Operations