Fabrication Guide for Seaboard®

The machining characteristics of Seaboard^® are excellent, but like all plastics, router tool selection is critical. There's no substitute for selecting the right tools for the job.

Cutting

Seaboard^® can be cut with a table saw, radial arm saw, CNC router, band saw, or panel saw. With any cutting process, the key is good sharp tools and chip removal, which helps eliminate heat build-up. A dull tool or improper feed rate can lead to rough edges and heat build-up to the point where chips start to melt and refuse. Always cut a test piece before a production run.

Circular saws – generally, carbide-tipped blades are recommended, and the following settings are useful starting points:

• Rake angle: 0 to 15°
• Clearance angle: 10 to 20°
• Cutting speed: 8,000 to 12,000 ft/min
• Feed rate: 70 to 90 ft/min
• Tooth pitch: 0.080" to 0.040"

Routing

Seaboard^® is a high-density polyethylene developed for the marine industry. This material is easily routed and engraved when router tooling is selected with the proper geometry.

Tool selection for general routing:
In the general machining of Seaboard^®, the right tool for the job involves the use of up-cut spiral router bits to evacuate the chip and maximize finish. The tools of choice include an Onsrund Cutter 52-080 and 63-725. These 1/4" diameter tools tested in 1/2" Seaboard^® provided an excellent finish in partial and full-depth cuts. The 52-080 performed best in full-depth cuts, while the 63-725 was quieter, which translates into less vibration and heat with increased tool life. The feed rate for the material was 100-200" per minute at 18,000 RPM, which reflects a shipload range of approximately 0.006 to 0.011. If the user were limited to a single tool selection, the 63-725 would represent the best all-around tool for the job. Unlike endmills, both of these router tools provide the necessary edge sharpness to alleviate the "fuzzing" or "hairing" sometimes associated with machining this material.

Drilling

Drilling in plastic has always been a problem in the plastic industry because of chip wrap in soft plastics and crazing in hard materials. A drill with a 60-degree point and a flat rake face provides the best plunge point in various plastics, including Seaboard^®. The point style creates a chip in soft plastic easily ejected and allows normal drilling routines during programming.

Things to keep in mind when machining Seaboard^®:

• Avoid straight plunge cuts into the material. Program the tool path to ramp into the material from the side, providing a path for the chips to be ejected.
• Select the shortest cutting edge possible to cover the material and achieve the cutting objective. Cutting edges that are too long for the application tend to cause vibration, adversely affecting the part finish.
• As material thickness increases, so should the diameter of the tool. Larger diameters are less susceptible to vibration and afford better chip removal.
• Ensure part rigidity by following proper spoil board techniques.
• Maximize dust collection to completely evacuate gummy chips produced by softer plastics.
• Properly maintain CNC routing equipment and give daily attention to collect and tool handling systems.
• Notch sensitivity – When machining or cutting the material, care should be taken to avoid notched, grooves, or score lines in the sheet. It is important to cut the material with a radius to help disperse the inherent stresses in the corner of a fabricated item. Sharp angles should be avoided.
• Thermal expansion and contraction – Seaboard^® is a high-density polyethylene product. Commonly with all plastic materials, the sheet expands when warmed and contracts when cooled. This is a reversible phenomenon; when it returns to the original temperature. It will return to the exact size it was originally. This property is called linear thermal expansion and  contraction.
  Thermal Expansion Coefficient for Seaboard^® = 0.00006 in/in/°F