Full Product Manual

11
Health and Safety Precautions
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 is a combustible thermoplastic
material. Observe fire precautions appropriate for comparable
forms of wood and paper products.
Machining
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.
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.
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.
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.
Plexiglas
®
acrylic sheet can be machined to close tolerances
and finished parts should be annealed (see page 30, Annealing
Plexiglas
®
Acrylic Sheet).
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.
Turning
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.
Plexiglas
®
acrylic sheet discs may be turned on a lathe. Circular
blanks should be rough cut with a band saw approximately
1
⁄
8 inch
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°.
MACHINING PLEXIGLAS
®
ACRYLIC SHEET