Routing acrylic sheet

ACRYLITE® Routing Fabrication Brief PDF

Manual Feed Routers

Many commercially available types of routers are acceptable. These include hand held routers, table routers, pin routers, and fixed position routers. The router should have a minimum of one horsepower and a no load speed of 20,000 RPM.

CNC (Computer Numerical Controlled) Routers

Computerized Numerical Control (CNC) machines are available from several manufacturers for high volume production. Today there are many companies manufacturing CNC routers servicing industries that fabricate wood, metal, and plastic products. As a result, a variety of machine designs are available to fit the job demand.

Light duty routers made for engraving or routing thin (0.118") single sheet, are commonly fitted with one to three horsepower spindle motors. Medium duty routers as seen in the sign industry use four to seven horsepower motors. Large volume and multiple head routers have motors ranging from seven to twenty horsepower.

There are three basic machine designs:

• Gantry type machines have an overhead beam that supports one or more routing heads or motorized spindles on a column. The column can be programmed to travel along the gantry beam, both horizontally and vertically. The beam, itself, rides on two vertical supports that travel along parallel tracks set on both sides of a stationary worktable. This facilitates a third axis of movement.
• Stationary bridge machines are similar to gantry type machines except that the bridge is stationary. The third axis of movement is facilitated by a worktable that can move in a horizontal plane perpendicular to the stationary bridge.
• Machining centers originate in the tool industry. They offer higher precision and are commonly used for the production of small component parts. These machines typically have smaller worktables than the stationary bridge or gantry machines and carry a higher price, corresponding to their accuracy and versatility.

All of these CNC machine types are available for purchase with hardware and software to facilitate machining on 2 ½, 3, 4, and 5 axis. There are machines to fit any requirement from fabrication of small prototypes to large part production runs. CNC machines can handle repetitive production cycles, using one or two tables. They are also available with multiple routing heads or spindles, so several parts can be produced at the same time. Options are available such as turret heads and tool changing spindles to facilitate tool changes without stopping the machine. CNC machines can be set up for semi-automatic or fully automatic operations that incorporate material pallet changers and automated loading and unloading equipment.

If business demands justify a step up in production, CNC routing is one of the best ways to increase productivity, as well as assure reproducible results and quality.

Router Bits

Router bits may be made of high-speed steel (HSS), carbide-tipped, solid carbide or diamond-tipped. They can be one piece, multiple part, bearing guided, straight cutting, forming or specialty bits.

Router bits for machining acrylic may consist of one to three flutes. Single and double fluted bits are commonly used.  When using HSS or brazed carbide bits, the length of the cutting edge should not exceed three times the diameter of the tool or a ratio of 3 to 1. With the proper use of solid carbide bit technology, this ratio can be increased to 4.5 to 1. Bit shank diameter should always be equal to or larger than the cutting tool diameter.  The length of the shank should be long enough so that the entire cutting edge is usable. Bits should be mounted in a clean collet chuck and set to allow maximum tool bit support and flute clearance to facilitate chip ejection.

Procedures

Be sure to follow the manufacturers’ safety recommendations for equipment and materials used with ACRYLITE® extruded acrylic sheet.

Safety

When using routing equipment always wear protective face shields or safety goggles.  Hearing protection is recommended for extended periods of routing.  If a vacuum system is not used, a respirator or dust mask will offer protection from dust particles.

Hand Routing

Prototype and replacement parts can be produced using a hand router. The router is guided around a precut template pattern that is fastened to the acrylic sheet. The template is typically held to the sheet using vacuum or two-sided adhesive tape. Clamps may also be used to hold the template to the material and moved when necessary. Templates can be made from plywood, fiberboard or rigid plastic. A hand-held router can be piloted around the pattern in several ways. Offsets can be calculated making allowances for the router sub-base, template guide, or a piloted bearing follower bit.

Direction of Travel

Proper feed direction is essential for a smooth cut. Routers rotate clockwise when viewed from the spindle or colleted side of the router. This is also referred to as Right Hand Cutting. If a hand held router is fed into the sheet in a clockwise direction, the cutting edges of the bit will pull the bit into the work rendering control nearly impossible. This routing method is referred to as Climb Cutting. Climb Cutting should only be used on machinery that has rigid spindles and worktables that are free of leadscrew backlash. Climb Cutting will improve product surface finish and increase tool life.

Note:This type of machining can only be done on CNC machinery. Climb Cutting is not recommended for most routing applications.

The feed direction for external cuts should be counterclockwise. When routing inside edges, the router should be fed clockwise. This practice will allow an operator to maintain proper control of the router and attain a smooth edge. This method is referred to as Conventional Cutting.

Note: Conventional Cutting is the recommended method for most routing operations. Refer to the routing direction diagram below.

Slotting, routing shapes out of a sheet, periphery routing, and cutting a part by machining around the outside edge of the part, employ both conventional and climb routing. Care should be taken in the machining techniques and programs to allow for the desired finish.

Vibration

It is of the utmost importance that balance of the tool, collet and spindle is maintained so that vibration is kept to a minimum. Even small vibrations can introduce stress that will eventually result in crazing and fractures in acrylic sheet during fabrication or use. The maintenance of spindles and collets is a key factor in controlling vibration. The spindle and collet must be thoroughly cleaned every time there is a bit change.

Operation Terminology and Formulas

Cutting Edge - The leading edge of the cutter tooth

Flute - The space between the back of one tooth and the face of the following tooth.

Axis - The imaginary straight line that forms the longitudinal centerline of the cutter.

Helix Angle - The angle that is formed as the cutting edge spirals around the outside of the tool. It is measured relative to the axis of the tool.

Shank - The portion of the cutter that is held in the spindle in order to drive the tool.

Diameter – Equals the largest outside cylindrical dimension of the cutting tool, measured at the cutting edge. Cutter diameter is normally dictated by the design of the part. The key consideration is material removal. Initial machining steps should employ the largest cutter diameter to rough out the part. Secondary cutting operations should utilize bits that match the proper radius or leave the required edge and surface finish on the sheet.

Speed – Surface Feet Per Minute (SFM), is the actual speed at which the cutting edge of the tool is striking the material. It is used to determine spindle Revolutions Per Minute (RPM). There are two formulas that relate these two values and take into consideration the tool bit diameter.

• SFM = 0.262 x Diameter (inches) x RPM
• RPM = 3.82 x SFM / Diameter (inches)

For most operations the RPM commonly runs between 10,000 to 20,000. Depending on bit diameter, the speed can be as low as 300 SFM and may run as high as 2400 SFM although it more commonly runs from 500 to 1500 SFM. This will change based on the demand for material removal and edge finish requirement. This is the first of three factors that will affect material finish.  

Chip load - Inches Per Tooth (IPT) corresponds to the amount of material removed by each tooth of the cutter, every time it contacts and passes the material. Sufficient chip load will create stability between the cutter and the work piece. The optimum chip load for acrylic sheet is 0.004” to 0.015”/tooth.

Feed Rate – Inches per Minute (IPM) is the distance that the cutting tool travels along the edge or surface of the material being processed in one minute. The proper range for feed rate can be determined by considering the chip load. Operating in the lower part of the recommended range for chip load will tend to provide a better finish, but at the expense of throughput.  Operating at the high end of the recommended range for chip load will result in a rough finish on the part but higher part throughputs. Typical feed rate parameters, for ACRYLITE acrylic sheet range from 100 to 300 IPM. To establish the feed rate knowing the desired chip load, the number of cutting edges on the bit and the RPM, use the following formula:

• IPM = IPT x No. Teeth x RPM