Scroll saws may be used for cutting sharp radii and closed holes in thin pieces of Plexiglas® acrylic sheet, but are less suitable for cutting thick sections or multiple sheets. Because of the short stroke, scroll saw blades do not clear the chips and tend to gum up. When this happens, the plastic softens and welds around the blade. Scroll saws must be used with a light feed and without forcing the work. The teeth should be cleared often. As soon as the blade stops cutting cleanly, it should be backed out, the chips removed, and the sheet cooled. Welding of the plastic behind the blade may be alleviated by using two blades mounted side by side, or by using an air blast to remove chips and cool the Plexiglas® acrylic sheet. A coolant may also be used. Masking material should always be left intact to provide lubrication in addition to protecting the sheet. Blades should be sharp with 10 to 14 teeth to the inch. Hold-downs are necessary to prevent vibration.
Portable saber saws may also be used for making either straight or curved cuts in Plexiglas® acrylic sheet. When using this type saw, however, it is necessary to provide adequate support for the Plexiglas® acrylic sheet, since the vibration caused by the reciprocating action of the saw blade may chip or crack the sheet. Chisel-type sabre
saws should be adjusted so that the cutting chisel stroke is about 3 ⁄ 6 i n c h e s g r e a t e r t h a n t h e t h i c k n e s s o f t h e w o r k t o b e c u t . T w o
thicknesses of corrugated fiberboard should be placed on the working surface under the Plexiglas® acrylic sheet. The stroke of the chisel should clear the upper surface of the sheet by about
1 ⁄ 1 6 i n c h a n d p e n e t r a t e i n t o t h e c o r r u g a t e d f i b e r b o a r d a b o u t 1 ⁄ 8 i n c h ,
thus driving the plastic chips into the board. The blade should be the same type used for scroll saws.
Veneer saws are small circular saws mounted on arbors and powered by high-speed electric or air motors. They are available as stationary or portable models. The saw blades are made in 3-inch and 4-inch diameters with several teeth per inch and have considerable set. They should be driven at 10,000 to 15,000 rpm to give a surface speed of 8,000 to 15,000 feet per minute. Veneer saws cannot be easily guarded and must be used with great care. Carbide-tipped blades should not be used unless designated for high-speed operations.
Portable veneer saws are most often used to trim large formed parts of Plexiglas® acrylic sheet held in trimming fixtures. (See Machining Plexiglas® Acrylic Sheet, page 11.) Stationary veneer saws can be used in woodworking shapers or routers for trimming the flanges of compound formed parts when the flange is on one plane. The height of the saw is adjusted to the proper distance above the table and the work is moved past the revolving blade.
A hole saw is a tubular tool with teeth filed on the lower edge of the tube. The teeth are set to cut a groove wider than the thickness of the tool wall. A shaft is fastened to the top of the tube so that it can be mounted in a drill press to drive the saw. Usually a pilot drill and guide are provided to locate and center the hole saw. Knockout holes are located in the top of the saw to allow r e m o v a l o f t h e d i s c s . H o l e s a w s a r e s t o c k e d i n s i z e s f r o m 5 ⁄ 1 6 - i n c to 4-inch diameters. Large-diameter hole saws may be made by inserting a piece of band saw blade in a groove machined in a steel disc and holding it with set screws. Coarse-tooth saws should be used for cutting Plexiglas® acrylic sheet. h
The Plexiglas® acrylic sheet should be cut halfway through, turned over, and the finishing cut made from the other side. When cutting sheet greater than 0.236 inches thick, a detergent/water lubricant and coolant should be used. A saw-cut hole is typically rough and often melted, requiring a post-finishing operation. Better quality holes can be achieved by machining with a router or circle cutter.