Health and Safety Precautions
If tools are sharp and properly ground, coolants are seldom required for machining Plexiglas® acrylic sheet. Coolants may be desirable for an unusually smooth finish or for deep cuts. If coolants are employed, only detergent in water or a compatible, soluble oil in water should be used. Other coolants may contain chemicals harmful to Plexiglas® acrylic sheet.
Machining Plexiglas® acrylic sheet should not result in harmful concentrations of vapors provided that adequate ventilation is employed. To insure this, both general and local exhaust ventilation are recommended. See Concentration Levels and Ventilation Standards, page 3.
Before using any soluble oils or wax sticks as machining aids for Plexiglas® acrylic sheet, review and follow each manufacturer’s recommendations for safe use of these products.
Plexiglas® acrylic sheet can be machined to close tolerances and finished parts should be annealed (see page 30, Annealing Plexiglas® Acrylic Sheet).
Plexiglas® acrylic sheet is a combustible thermoplastic material. Observe fire precautions appropriate for comparable forms of wood and paper products.
The usual rules of good machining practice apply to the machining of Plexiglas® acrylic sheet. An experienced machinist should have no difficulty handling Plexiglas® acrylic sheet as soon as he gets the feel of the material. Acrylic has working qualities similar to those of brass and copper.
For applications that require both close tolerance and good optical properties, such as periscope prisms and lenses, acrylic blanks should be annealed before and after rough machining. The parts may then be machined to close tolerance, removing as little material as possible. When final machining is complete, the parts should be given a final annealing. Since temperature and humidity affect the dimensions of Plexiglas® acrylic sheet, machining to close tolerance must be done under conditions like those that will prevail when the parts are tested and put into service.
Tools and work should be held firmly to prevent chattering. Standard metal- or wood-working equipment can be used, such as milling machines, drill presses, lathes, planers and shapers. In general, machining tools should be operated at high speeds with moderate feed rates. Tools should be sharp, clean and free of nicks and burrs.
Plexiglas® acrylic sheet can be turned on a lathe to give an excellent semi-matte surface. Surface speeds of 500 feet per minute with feeds of 0.004 to 0.005 inches per revolution will cut a clean continuous chip. If the feed stops, the Plexiglas® acrylic sheet may be marked. The maximum permissible depth of cut is controlled by the rigidity of the section being turned.
Because it is a thermoplastic material, Plexiglas® acrylic sheet softens when heated to its forming temperature. The frictional heat generated by machining tends to soften the material in the immediate vicinity of the cut, and causes gumming and sticking of the tool or tearing of the plastic if excessive heat buildup occurs. When proper speed, feed and cutters are used, machined Plexiglas® acrylic sheet surfaces will have an even, semi-matte surface, which can be brought to a high polish by sanding and buffing.
Plexiglas® acrylic sheet discs may be turned on a lathe. Circular
b l a n k s s h o u l d b e r o u g h c u t w i t h a b a n d s a w a p p r o x i m a t e l y 1 ⁄ 8 i n c h
over size. The 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 off-center, so the waste is thrown clear. The cutting tool should be ground to a rake angle of 0° to 5°.