TURNING

Vical acrylic can be turned on a lathe to give an excellent semi­matte surface. Surface speeds of 500 feet per minute with feeds of .004" to .005" per revolution will cut a clean continuous chip. If the feed stops, the Vical acrylic may be marked. The maximum permissible depth of cut is controlled by the rigidity of the section being turned.

Vical acrylic discs may be turned on a lathe from square stock. Square blanks are clamped between the face plate and a tailstock fitted with a live center and a pressure pad. The blanks should be mounted slightly off­center so the waste is thrown clear. The cutting tool should be ground to zero horizontal rake angle and fed at a 3° to 5° angle.

ROUTING AND SHAPING

Wood working shapers (also called table routers) and overhead or portable routers are used in edge finishing operations and for cutting flat or formed Vical acrylic parts to size. For edging small parts, the table router is convenient; portable routers are useful wherever the Vical acrylic part is too large or awkward to bring to the machine.

Routers should have a minimum no­load spindle speed of 10,000 r.p.m. Higher speeds 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 straight fluted cutters 5/16 to1/2" in diameter will produce good cuts. Smaller diameter cutters should be used with care. If cutters larger than 1/2" in diameter are used, the material should be machine fed rather than hand fed to overcome chatter. For safety, cutter shanks should be at least h" in diameter. Single fluted cutters should not be used under any circumstances.

When machining thick sections of Vical acrylic, 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.

Machining Acrylic Sheet

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 degrees and a positive rake angle of up to 15 degrees.

The most common operations performed with routers are deflanging and flange trimming. Such cuts may be made with router cutters or with veneer saw blades attached to portable or table routers by suitable arbors.

When deflanging cuts must be made to close tolerances, fixtures should be used to support the Vical acrylic 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. The Vical acrylic 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 saws can be used for flange trimming and will produce a good quality edge. For high accuracy trimming, 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.

Portable routers or table shapers equipped with wood working router bits are also commonly used in this operation. Depending on the equipment used, a template may or may not be necessary. 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.