Machining Acrylic Sheet
This brief gives advice for:
- Trouble Shooting
Many types of machining equipment are used in fabricating ACRYLITE® products. Some include millers, grinders, thread cutters, engraving equipment, files, and reamers.
Most equipment used in machining ACRYLITE® was originally designed for wood or metal. Notching or overheating sheet due to inadequate equipment or improper cutting tools may cause failure of the fabricated item. To prevent this, make sure equipment is right for ACRYLITE® sheet.
Various kinds of machines are available for milling ACRYLITE® sheet. Machines with a heavy base and reliable balance are needed to control vibration and assure clean cuts. Equip all units with vacuum devices or compressed air to clear chips and cuttings from the blade area, and to control heat generation.
Milling cutters vary widely, depending on the application. Cutting edge rake angle should be 0-5° and clearance angle 2-10°. You can machine ACRYLITE® sheet with high speed steel, carbide, or diamond-tipped tools.
Carbide tools, though they have a higher initial cost than steel, maintain a sharp edge longer, producing a high-quality machined edge for a longer time. Diamond-tipped tools produce a superior cut and last even longer than carbide-tipped tools. Pigments in ACRYLITE® sheet colors may shorten tool edge life.
You can use most normal files, hand routing files, and rasps with ACRYLITE® sheet. The tool depends on the desired effects and the application. Use these tools for producing a rough surface, not for fine finishing.
For artistic work, use flexible shaft engravers rotating at least 1000 rpm and air operated pencil milling and grinding tools rotating about 6000 rpm.
Use normal reamers for deburring drilled holes. Be sure all tool edges are fault-free, preventing grooves or furrows in the drilled surface.
Use normal taps and dies to cut internal and external threads in ACRYLITE®. Most machine cutters are suitable.
When using machining equipment, wear a protective face shield or safety goggles. Wear hearing and respiratory protection if you will be operating equipment for a long time.
Follow normal workshop safety practices when machining ACRYLITE®. Eye, ear, and respiratory protection may be appropriate, depending on the operation.
Be sure to follow manufacturers' safety recommendations for equipment and materials used with ACRYLITE® sheet.
Direction of Travel
To achieve a smooth cut, feed the sheet in the proper direction as required by the tool rotation.
Feed material into the rotating edge of the cutter.
Stresses inherent in ACRYLITE®, as well as stresses imparted to fabricated articles by machining, may cause dimensional changes when sheet is heated to the forming temperature (300°F) after machining.
Anneal the part to eliminate stresses. See Fabrication Tech Brief #12, Annealing.
To use a single-edged cutter, carefully balance the chuck with adjusting screws to eliminate chatter marks. Edge quality will depend largely on the machine's stability.
Use a multi-edged milling tool. The cutter's rotation speed should be as fast as possible, at least 3300 feet per minute.
As most blades are designed for machining wood or metal, modifications may be necessary. The rake angle should be 0°, reducing chipping by providing a scraping, rather than cutting, action. The clearance angle should be at least 2°, usually more, to minimize frictional heat buildup. If you're using a standard milling tool, provide cooling.
Plastics, including ACRYLITE®, are much more susceptible to heat distortion than metals. Use coolants such as compressed air, water, emulsions, etc., to minimize heat distortion effects and produce a polished surface. If cooling is not provided, decomposition and irregularities at the cut edge may produce high-stress areas, leading to crazing (numerous tiny cracks in the material).
If you use emulsions, have them tested for compatibility with acrylic. Incompatible emulsions may cause crazing.
If necessary, use a scraper made of high-speed steel to smooth sawn edges, eliminating notching. Flat-ground triangular files with a maximum edge width of 8 mm (3/10") are also effective. The file surface must not be hollow ground, as this will produce chatter marks due to the rake angle. A flat-ground file should have a 0° rake angle. As with sanding, use water for a smooth finish and less stress buildup from frictional heat.
Use hand-held tools for artistic applications and fixed-tracing engravers for precise work. Adjust the engraving tip's travel speed to avoid melting (whitening of the surface) from slow travel and chipping from fast travel. If melting persists, use a liquid coolant or air cooling.
Due to the notch sensitivity of acrylics, don't machine threads with sharp edges. To reduce stresses, use rounded threads. Note, too, that threads should not be intended to bear loads. If threaded connections will often be unscrewed, reinforce the internal thread with a metal insert.
Use a cutting emulsion or oil to produce a polished surface. Regularly remove chips from internal holes, and don't allow the tap to "bottom out.”
|Trouble Shooting when Machining Acrylic Sheet|
|Chatter Marks||Dull tool||Replace or sharpen tool|
|Feed rate too fast||Reduce feed rate|
|Unbalanced chuck||Balance chuck with adjusting screws or replace chuck and spindle|
|Bearing wear||Replace when runout exceeds 0.002“|
|Incorrect rake angle||Use tool with 0° rake angle|
|Melted Edges||Dull tool||Replace or sharpen tool|
|Slow feed rate||Increase feed rate|
|No cooling||Add compressed air, water, mist, or emulsion cooling|
|Chip buildup||Use vacuum system or compressed air to clear chips|
|Incorrect rake angle||Use tool with 0° rake angle|
|Incorrect clearance angle||Use tool with 2-10° clearance angle|
ACRYLITE® sheet is a combustible thermoplastic. Precautions should be taken to protect this material from flames and high heat sources. ACRYLITE® sheet usually burns rapidly to completion if not extinguished. The products of combustion, if sufficient air is present, are carbon dioxide and water. However, in many fires sufficient air will not be available and toxic carbon monoxide will be formed, as it will when other common combustible materials are burned. We urge good judgement in the use of this versatile material and recommend that building codes be followed carefully to assure it is used properly.
Like other plastic materials, ACRYLITE® sheet is subject to crazing, cracking or discoloration if brought into contact with incompatible materials. These materials may include cleaners, polishes, adhesives, sealants, gasketing or packaging materials, cutting emulsions, etc. See the Tech Briefs in this series for more information, or contact your ACRYLITE® sheet Distributor for information on a specific product.
This information and all further technical advice is based on our present knowledge and experience. However, it implies no liability or other legal responsibility on our part, including with regard to existing third party intellectual property rights, especially patent rights. In particular, no warranty, whether expressed or implied, or guarantee of product properties in the legal sense is intended or implied. We reserve the right to make any changes according to technical progress or further developments. The customer is not released from the obligation to conduct careful inspection and testing of incoming goods. Performance of the product described herein should be verified by testing, which should be carried out only by qualified experts in the sole responsibility of a customer. Reference to trade names used by other companies is neither a recommendation, nor does it imply that similar products should be used.
These products are sold under the registered trade name ACRYLITE® in the Americas and under the PLEXIGLAS® trade name on the European, Asian, African and Australian continents.
Roehm America LLC Acrylic Products 1796 Main Street Sanford, ME 04073 USA Phone +1 800 631-5384 www.acrylite.co
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